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Java8 Feature

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Logicmojo - Updated Dec 12, 2023

Java 8 was launched on March 14, 2014, and according to Java, it is the most recent release for Java that provides new features, upgrades, and bug fixes to improve the efficiency with which Java programs are developed and run.
Java, which originated from the Oak programming language, was released in early 1996 with Java 1 (JDK 1.0) as its major version. Sir James Gosling of Sun Microsystems was the first to create and develop Java. One of the major releases of the Java programming language in 2014 is Java 8, often known as JDK 8.0. Spider is another code name for it. Oracle Corporation now manages Java, which is an open-source project.
Java is a widely used programming language, with applications ranging from Android apps to the Internet of Things (IoT). According to Codeplatoon, Java was the most popular programming language in job postings in 2019. Given its widespread use, it's no wonder that people who are knowledgeable in Java continue to be in great demand.

Cracking SDE Roles in Top Product Companies

That's why we've compiled a list of the most often asked Java 8 questions and answers in job interviews. It's not enough to have considerable expertise and knowledge in a particular field (in this case, for instance, Java). You must organise your ideas, study the relevant facts, and concentrate on the most often asked questions.

We’ll begin with the basics of Java 8 and work our way up to the tougher questions. Once you get through this material, you will be in a better position to own that critical interview!

So, let’s dive deep into the surplus of useful interview questions on Java8.

Java 8 Features by Logicmojo

⌚ What New Features Did Java 8 Include?

There are various new features in Java 8, but the following are the most important:

Lambda Expressions −a new feature of the language that allows us to consider actions as objects
Method References − allow us to define Lambda Expressions by explicitly referring to methods by their names
Optional − Optionality is expressed via a special wrapper class.
Functional Interface – A Lambda Expression can be used to implement an interface with a maximum of one abstract method.
Default methods − allow us to provide entire implementations in interfaces in addition to abstract methods
Nashorn, JavaScript Engine − JavaScript code execution and evaluation engine based on ava.
Stream API −a particular iterator class that lets us to efficiently process collections of items
Date API −a Date API inspired by JodaTime that is enhanced and immutable

Along with these new features, lots of feature enhancements are done under the hood at both the compiler and JVM level.

⌚What are functional or SAM interfaces?

An interface with only one abstract method is known as a functional interface. As a result, it's also known as the SAM (Single Abstract Method) interface. Because it covers a function as an interface, or in other words, because a function is represented by a single abstract method of the interface, it's called a functional interface.

Default, static, and overridden methods can all be found in functional interfaces. The @FunctionalInterface annotation can be used to declare Functional Interfaces. This annotation will cause a compiler error if it is used on interfaces with more than one abstract method.

@FunctionalInterface
  
interface Square {
    int calculate(int x);
}
  
class Test {
    public static void main(String args[])
    {
        int a = 5;
  
        // lambda expression to define the calculate method
        Square s = (int x) -> x * x;
  
        // parameter passed and return type must be
        // same as defined in the prototype
        int ans = s.calculate(a);
        System.out.println(ans);
    }
}

        Try it Yourself

⌚ What Is a Default Method, and When Should It Be Used?

A default method is an interface method that has an implementation.To add new functionality to an interface while keeping backward compatibility with existing classes that implement the interface, we can utilise a default method:

public interface Vehicle {
    public void move();
    default void hoot() {
        System.out.println("peep!");
    }
}

When a new abstract method is added to an interface, all implementing classes will break until the new abstract method is implemented. The default method was used to fix this problem in Java 8.

The Collection interface, for example, lacks a forEach function declaration. As a result, implementing such a method would disrupt the entire collections API.

The default method was introduced in Java 8 to allow the Collection interface to provide a default implementation of the forEach method without requiring the classes that implement this interface to do so.

⌚ What are the significant advantages of Java 8?

Compact, readable, and reusable code.
Code is more concise and readable
There will be less boilerplate code.
Operation and execution in parallel.
Can be used on a variety of operating systems.
High stability.
Stable environment.

⌚ What are Lambda Expressions in Java?

Java lambda expressions were the platform's first foray towards functional programming. An unnamed expression or function that is recast as a parameter for any other function is known as a Java Lambda Expression or Lambda Function. In Java, lambda expressions are functions that can be shared as an object. It can also be used to refer to a specific thing. Lambda Expressions require more compact coding, as well as implementing a mechanism for executing Java 8's functional interfaces. In Java, lambda expressions allow users to express a single functional unit that can be reused over multiple lines of code.

Lambda Expressions Syntax:

(Argument List)-> {expression;}

Example

public class LambdaExpressionExample{  
    public static void main(String[] args) {  
    // using lambda Expression  
        new Thread(():>System.out.println("Thread is started: using Lambda Expressions")).start();  
        // old way  
        new Thread(new Runnable() {  
            @Override  
            public void run() {  
                System.out.println("Thread is started: using old method");  
            }  
        }).start();  
    }  
}

Output

Thread is started: using the old method
Thread is started: using Lambda Expressions

⌚ Describe some of the Standard Library's functional interfaces.

The java.util.function package has a large number of functional interfaces. Among the most frequent include, but are not limited to:

Function – It accepts only one parameter and produces a result.
Consumer – It only accepts one argument and produces no output (represents a side effect)
Supplier – It accepts no input and outputs a result.
Predicate – It accepts a single parameter and returns a boolean value.
BiFunction – It is a function that takes two inputs and returns a result.
BinaryOperator – It works in a similar way to a BiFunction in that it takes two arguments and returns a result. The two arguments, as well as the outcome, are of the same sort.
BinaryOperator – It's comparable to a Function in that it takes a single argument and returns the same type of result.

⌚Describe the rules that users should adhere to when utilising Java Functional Interfaces.

When using the Java programming language's Functional Interfaces, the user must adhere to a number of rules. These are the rules:

There should only be one abstract method in the functional interface. It can, however, have any number of static and default methods.
Only one abstract method is allowed in Java functional interfaces. In functional interfaces, we can't use more than one abstract method.
When defining a functional interface in Java, the annotation @Functionalinterface should be used.
If we override a method from the Java.lang.object class in a functional interface, it will not be counted as an abstract method.
In order to define a number, we can use any method.

⌚Describe in brief about the method references in Java?

In the most advanced version of Java, Java SE 8, method references were added to the programming language. In Java, method references are an additional definitely great feature that was added in Java SE 8. With the help of Method references, Lambda Expressions have gained a little more oomph and flexibility. In Java SE 8, method references are a subset of the lambda expression that invokes (references) methods by applying a method name.

In other words, in Java, method references have typically reduced the number of Lambda Expressions that are used to invoke methods. When a lambda expression declares a function and does nothing else, method references are used. In Java, two integer colons (::) denote method reference.

Example

interface Printing{       
    void print();    
}    
public class Example1 {    
    public static void printAnything(){    
        System.out.println("LogicMojo is a great website to learn.");    
    }    
    public static void main(String[] args) {   
        // Referring static method    
        Printing printer= MethodReference1::printAnything;    
        // Calling interface method    
        printer.print();    
    }    
}

⌚Explain the Lambda Expression's Syntax and Characteristics.

The parameter part and the expressions part of a lambda expression are separated by a forward arrow:

params -> expressions

The following are the features of any lambda expression:

Optional type declaration — we don't need to declare the types of the parameters on the left-hand side of the lambda because the compiler can infer them from their values. As a result, int param ->... and param ->... are both legal.
Optional parentheses - we don't need to use parenthesis when only one parameter is declared. This indicates that param ->... and (param) ->... are both legal, but parentheses are necessary when more than one parameter is provided.
Optional curly braces – Curly braces are not required when the expressions component contains only one statement. This indicates that param – > statement and param – > statement; are both legitimate options, but curly brackets are required when several statements are present.
Optional return statement – We don't require a return statement if the expression returns a value and is enclosed in curly braces. As a result, both (a, b) – > return a+b; and (a, b) – > a+b; are correct.

⌚ what is optional class in java? How can we use it?

Optional is a new Java 8 class that encapsulates an optional value, that is, a value that can be present or absent. It's an object wrapper, and we can think of it as a container with zero or one elements.

Instead of wrapped null, Optional provides a special Optional.empty() value. In many circumstances, it can be used instead of a nullable value to avoid NullPointerException.

Optional's major purpose, according to its designers, is to be a return type for methods that previously returned null. Such methods would necessitate writing boilerplate code to check the return value, and we might forget to run a defensive check every now and again. Optional return types in Java 8 require us to treat null and non-null wrapped data differently.

The Stream.min() method, for example, calculates the minimum value in a stream of values. But what happens if the stream is dry? The method would return null or throw an exception if it weren't for Optional.

It does, however, return an Optional value, which may or may not be Optional. empty() is a function that returns nothing (the second case). As a result, we can easily deal with the following situations:

int min1 = Arrays.stream(new int[]{1, 2, 3, 4, 5})
  .min()
  .orElse(0);
assertEquals(1, min1);

int min2 = Arrays.stream(new int[]{})
  .min()
  .orElse(0);
assertEquals(0, min2);

It's worth noting that, unlike Option in Scala, Optional is not a general-purpose class. It is not advised that we utilise it as a field value in entity classes, as its lack of implementation of the Serializable interface indicates

⌚ What Exactly Is a Stream? What Sets It Apart From a Collection?

A stream is a simple iterator that accepts a series of actions to be applied to each of the elements it contains.

A stream is a collection of items from a single source that can be utilised to execute aggregate operations. They were designed to make collection processing as straightforward as feasible. Unlike collections, the iteration mechanism is handled within the stream, allowing us to use methods like map and flatMap to perform declarative processing.

The Stream API is also fluent and supports pipelining:

int sum = Arrays.stream(new int[]{1, 2, 3})
  .filter(i -> i >= 2)
  .map(i -> i * 3)
  .sum();

Streams are also distinct from collections in that they are inherently slow to load and process data.

⌚ What are the distinctions between intermediate and terminal operations?

To process streams, we aggregate stream operations into pipelines. All operations fall into one of two categories: intermediate or terminal.

Intermediate operations are those that return Stream, allowing for other operations on a stream to be performed.

These actions are always lazily executed, meaning they do not process the stream at the call site. Only when a terminal operation is present may an intermediate operation process data. Filter, map, and flatMap are examples of intermediate processes.

Terminal activities, on the other hand, end the pipeline and begin stream processing. During a terminal operation call, the stream is sent through all intermediate operations. forEach, reduce, Collect, and sum are examples of terminal operations.

Let's look at an example with side effects to illustrate this point:

public static void main(String[] args) {
    System.out.println("Stream without terminal operation");
    
    Arrays.stream(new int[] { 1, 2, 3 }).map(i -> {
        System.out.println("doubling " + i);
        return i * 2;
    });
 
    System.out.println("Stream with terminal operation");
        Arrays.stream(new int[] { 1, 2, 3 }).map(i -> {
            System.out.println("doubling " + i);
            return i * 2;
    }).sum();
}

The intermediate operations are only activated when a terminal action is present, as we can see.

⌚ What's the Difference Between Map and FlatMap Streaming?

Between map and flatMap, there is a signature difference. A Map operation encapsulates its return value inside its ordinal type in general, whereas flatMap does not.

A map operation in Optional, for example, returns OptionalString> type, whereas flatMap returns String type.

So, after mapping, we must unwrap (read: "flatten") the object in order to extract the value, whereas after flat mapping, we do not need to do so because the object is already flattened. In Stream, we use the same notion for mapping and flat mapping.

Both map and flatMap are intermediate stream operations that take a function and apply it to all of a stream's elements.

The difference is that while this function returns a value for the map, it returns a stream for flatMap. The flatMap operation combines the streams into a single stream.

Here's an example of how we can "flatten" a map of users' names and phone listings into a list of all users' phones using flatMap:

Map<String, List<String>> people = new HashMap<>();
people.put("John", Arrays.asList("555-1123", "555-3389"));
people.put("Mary", Arrays.asList("555-2243", "555-5264"));
people.put("Steve", Arrays.asList("555-6654", "555-3242"));

List<String> phones = people.values().stream()
  .flatMap(Collection::stream)
    .collect(Collectors.toList());

⌚ In Java 8, what is Stream Pipelining?

The concept of stream pipelining is the linking of operations. This is accomplished by dividing the possible operations on a stream into two categories: intermediate operations and terminal operations.

Each intermediate operation returns an instance of Stream itself when it runs. As a result, we may create a processing pipeline with an arbitrary number of intermediary actions to process data.

The pipeline must then be terminated using a terminal operation that returns a final value.

⌚What are the benefits of utilising the Optional class over other classes?

The following are the primary benefits of utilising the Optional class:

It encapsulates optional data, such as null or not-null values, to prevent null checks, resulting in cleaner, more readable, and more robust code. It wraps the object and returns an object rather than a value, which can be utilised to avoid NullPointerExceptions during runtime.

⌚ What are the different types of data objects that a Stream can handle?

The following data can be processed by a Stream:

An Array's collection.
An input device or an I/O channel.
A reactive source (for example, social media comments or tweets/retweets)
A static factory or a stream generator function.

⌚Which intermediate operations are the most typically used?

Filter(Predicate) - Selective processing of Stream items is possible. It returns elements that satisfy the predicate's specified condition.
map(Funtion) - Returns a new Stream with each element transformed using the specified mapper function. = sorted() - Sorts the input elements before moving on to the next step.
distinct() - Only pass elements on to the next level; they haven't been passed yet.
limit(long maxsize) - Set the maximum size of the stream to maxsize.
skip(long start) - Leave the first few elements to the very beginning.
peek(Consumer) - Apply a consumer to the stream without making any changes.
flatMap(mapper) - Transform each element into a stream of its constituent elements, then combine all of the streams into one.

⌚In Java8, what is Nashorn?

Nashorn is the Java platform's new Javascript processing engine, which debuted with Java 8. Until JDK 7, the Java platform used Mozilla Rhino as a Javascript processing engine for the same reason.

Nashorn outperforms its predecessor in terms of conformance to the ECMA normalised JavaScript standard and runtime performance.

⌚ Tell Us About Java 8's New Date and Time API

The lack of support for date and time manipulations required by ordinary developers has been a long-standing issue for Java developers.

Existing classes like java.util.Date and SimpleDateFormatter aren't thread-safe, which could cause problems for users.

In the previous Java Data API, bad API design was also a reality. Here's a simple example: years in the java.util package The date begins at 1900, the months begin at 1, and the days begin at 0, which is counterintuitive.

Third-party date and time libraries, such as Joda-Time, have grown in popularity as a result of these and other concerns.

To address these issues and give better support in JDK, a new date and time API has been built for Java SE 8 under the package java.time, which is free of these issues.

⌚ In Java SE 8, what do you mean by Streams?

In Java SE 8, a new package called java.util.stream is implemented. The package includes a variety of interfaces, classes, and enums that allow users to execute functional actions on the items. Java streams are designed to make functional-style procedures on streams of elements easier.

A Java stream isn't a data structure by any means. Java Stream, on the other hand, can be considered an abstraction. Java Streams, on the other hand, is neither a collection or set in which we can preserve elements and data. The main distinction between a structure and a stream is that the latter does not store the data and components. A stream is a representation of an immutable collection of processes that are applied to any data classification.

In simple terms, a Java Stream is a package that comprises numerous classes and interfaces capable of internally iterating their own items. When working with the iteration characteristics of Java Collections, on the other hand, we must conduct the iteration of the items ourselves. (To interact with a Java Iterable, for example, we can use a Java Iterator or the Java for each loop.)

⌚ What are the two types of common Java Streams operations?

There are two different sorts of operations in Java Stream:

Intermediate operations: Intermediate operations return a stream, allowing the user to chain together several intermediate operations without needing semicolons, as in other programming languages such as Scala.

Terminal operations: The terminal operations are those that are mostly void and null, and if they aren't null, they return a non-stream as a consequence.

⌚ What's the difference between Streams and Collections?

S. N.	Collections	Streams
1.	Since Java SE 1.2, the Collection API has been available for use.	Java SE 8 included the Streams API.
2.	Data is stored using the collections framework. To put it another way, it is used to store a collection of objects.	Data is computed using streams. To put it another way, it is used to compute a set of objects.
3.	Both the Spliterator and the Iterator can be used to iterate elements in the Collections API. The user can also use the forEach() function to conduct a procedure on every element in the stream.	The Spliterator and Iterator are not allowed to iterate the elements of the stream in the Streams API.
4.	It's a method of storing an endless number of elements.	If users want to process the items of Collections, they can utilise the Streams API.
5.	To iterate the items of the stream, such as the Iterator, the Collections API use the external iteration concept.	Internal iteration is used by the Stream API to iterate the stream's items. Internal iteration is performed by the Streams API using the forEach() method.
6.	The Collections API's objects aren't built on the fly. The Collections' objects are eagerly built.	The Streams API creates objects in a lazy manner.
7.	When the collection object is completely computed in Collections, only the user can add elements to the collection object.	When the stream object is completely computed in Streams, the user is the only one who may add elements to the stream object. In basic terms, the Streams objects are computed in response to the user's request.
8.	When utilising the Collections API, a user can iterate and use elements from the collection's object as many times as they like.	When utilising the Streams API, a user can only iterate through and use elements from the stream's object once.

⌚ What are some of the most common Terminal operations in the Java programming language?

The following are some of the most popular Terminal operations in the Java programming language:

Stream.forEach(): The forEach() method or operation in the Java Stream is one of the terminal operations that begins the internal iteration of the stream's components. To put it another way, the Java Stream forEach() function aids in looping through all of the components of a stream and performing some action on each of them. The forEach() method returns void, which means it returns nothing. The Java lambda expression is used to represent the procedure that will be run on the stream's elements.
Stream.collect(): To grab elements from a stream and save them all in a collection, use the Java Stream.collect() function. Stream collect() is a method for extracting a solid combination of data from a stream's environment, such as an array list or a list. The Java Stream collect() function starts the internal iteration of elements and collects the elements in the stream into a collection or object of some form.
Stream anyMatch(): The anyMatch() function of the Java stream is also a terminal operation that accepts a single Predicate or condition as a parameter and initiates the Stream's internal iteration. The anyMatch() method applies the Predicate given to all Stream components. The anyMatch() method returns true if the supplied Predicate is true for any of the stream's components. AnyMatch() will return false if no elements match the Predicate.
Stream allMatch(): The allMatch() function of the Java stream is also a terminal operation that accepts a single Predicate or condition as an argument and initiates the Stream's internal iteration. The allMatch() method applies the Predicate given to all Stream components. The allMatch() method returns true if the supplied Predicate is true for all of the stream's components. AllMatch() will return false if not all of the elements match the Predicate.
Stream noneMatch(): The noneMatch() function of the Java stream is also a terminal operation that accepts a single Predicate or condition as a parameter and initiates the Stream's internal iteration. The noneMatch() method applies the Predicate given to all Stream components. If no elements are matched by the Predicate, the noneMatch() method will return true, and if one or more elements are matched by the Predicate, it will return false.
Stream.count(): The count() method of the Java Stream class is also a terminal operation that returns the number of components in the stream. The total number of elements in the stream is calculated and returned as a long return type. To put it another way, the Java Stream count() function begins an internal loop of the entries in the Stream and counts the elements that are present.
Stream.reduce(): The Java Stream reduce() method is likewise a terminal operation that allows you to reduce all of the stream's components to just one. The reduce() method applies the specified function on the stream's components and reduces them. The reduce() method returns an Optional (a process of restoring a nullable T reference with a non-null value), which maintains the stream's reduced value.

⌚ What is the best scenario for a user to use the Java Streams API?

The Stream API in Java 8 is useful in a variety of situations. These are the scenarios:

When a user needs to do database operations, the Streams API is invoked.
The Streams API is used to perform operations in a lazy manner.
IT aids in the development of functional-style programming.
It's used to run multiple processes at the same time.
When a project necessitates the use of pipeline operations, the Streams API is used.
The Streams API is quite handy for achieving internal iteration.

⌚ What is the distinction between an Iterator and a Spliterator?

The following are the differences between Iterator and Spliterator:

1. Introduction: Spliterator was first introduced in JDK 1.8, whereas Iterator was first introduced in JDK 1.2.

2. Use in API: Collection API uses Iterator, but Stream API uses Spliterator.

3. Parallel programming: Spliterator may be used to iterate the elements in a Stream in parallel or sequential order, while Iterator can iterate the elements in a Collection in sequential order.

4. Universal Iterator: Spliterator is not a universal iterator, whereas Iterator is.

⌚ What is the difference between Function and Predicate in Java 8 and how are they similar?

Difference:

Return Type: It's a single-argument function that returns an Object.The predicate function has a single input and returns a boolean value (true or false).

Similarities:

Both are functional interfaces, with a single abstract method in each.

⌚What problems do the old Date and Time APIs have? Can you describe the new Java 8 Date and Time APIs?

Prior to Java 8, there were old Date and Time APIs. Let's look at the problems they're having:

Performance: In terms of performance, Java 8 APIs outperform earlier Date and Time APIs.
Standards: The new Java 8 Date and Time API adheres to ISO standards, whereas the previous Java 8 Date and Time API was difficult to use and poorly conceived.
Thread-safe: java.util is the most commonly used package. Date is thread-safe yet changeable. New Java 8 Date and Time API are thread-safe.

LocalDateTime, LocalDate, and LocalTime are some of the most recent Java 8 core API classes.

⌚ What's the Difference Between Map and FlatMap Streaming?

FlatMap Stream delivers zero or more output values per input value, whereas Map Stream gives one output value per input value.

Map Example – The Map Stream operation is commonly used for simple Stream operations like the one below.

In this programme, we used the map operation to convert the characters in "Names" to upper case after putting them in a Stream, then we printed each element using the forEach Terminal method.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class Main {
    public static void main(String[] str) {
        List<String> Names = Arrays.asList("Saket", "Trevor", "Franklin", "Michael");
 
        List<String> UpperCase = Names.stream().map(String::toUpperCase).collect(Collectors.toList());
        // Changed the characters into upper case after converting it into Stream
 
        UpperCase.forEach(System.out::println);
        // Printed using forEach Terminal Operation
    }
}

        Try it Yourself

flatMap Example – For more complicated Stream operations, the flatMap Stream technique is employed.

We've done a flatMap operation on a "List of Lists of type String" here. We created a list of input names and then stored them in a Stream, filtering out the names that begin with the letter 'S.'

Finally, we printed each piece with the help of the forEach Terminal operation.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class flatMap {
    public static void main(String[] str) {
        List<List<String>> Names = Arrays.asList(Arrays.asList("Saket", "Trevor"), Arrays.asList("John", "Michael"),
                Arrays.asList("Shawn", "Franklin"), Arrays.asList("Johnty", "Sean"));
         
        /* Created a “List of List of type String” i.e. List&lt;List&lt;String&gt;&gt; 
           Stored names into the list
         */
 
        List<String> Start = Names.stream().flatMap(FirstName -&gt; FirstName.stream()).filter(s -&gt; s.startsWith("S"))
                .collect(Collectors.toList());
         
        /* Converted it into Stream and filtered 
            out the names which start with 'S'
         */
         
        Start.forEach(System.out::println);
         
        /*
         Printed the Start using forEach operation
         */
    }
}

⌚In Java 8, what is MetaSpace?

A new capability for storing classes was added in Java 8. MetaSpace is the location where all of Java 8's classes are kept. MetaSpace has replaced the PermGen.

The Java Virtual Machine used PermGen to store classes until Java 7. Java 8 replaced PermGen with MetaSpace because MetaSpace is dynamic and can grow indefinitely. It also has no size restriction.

⌚ In Java 8, what is the StringJoiner class? How can we use the StringJoiner Class to join several Strings?

StringJoiner is a new class in the java.util package that was introduced in Java 8. We can use this class to connect several strings separated by delimiters, as well as provide a prefix and suffix.

We will learn how to use the StringJoiner Class to join multiple Strings in the application below. "," serves as a delimiter between two strings in this case. Then, with the help of the add() method, we combined five separate strings together. Finally, the String Joiner was printed.

import java.util.StringJoiner;
 
public class Java8 {
    public static void main(String[] args) {
 
        StringJoiner stj = new StringJoiner(",");
        // Separated the elements with a comma in between.
         
        stj.add("Saket");
        stj.add("John");
        stj.add("Franklin");
        stj.add("Ricky");
        stj.add("Trevor");
         
        // Added elements into StringJoiner “stj”
         
        System.out.println(stj);
    }
}

        Try it Yourself

⌚ Create a Java 8 programme that adds a prefix and suffix to a String.

The delimiter "," is used to separate two strings in this application. We've also used the brackets "(" and ")" as a prefix and suffix. Then five different strings are joined by adding them with the help of the add() method. Finally, the String Joiner was printed.

import java.util.StringJoiner;
 
public class Java8 {
    public static void main(String[] args) {
 
        StringJoiner stj = new StringJoiner(",", "(", ")");
         
        // Separated the elements with a comma in between.
        //Added a prefix "(" and a suffix ")"
         
        stj.add("Saket");
        stj.add("John");
        stj.add("Franklin");
        stj.add("Ricky");
        stj.add("Trevor");
         
        // Added elements into StringJoiner “stj”
         
        System.out.println(stj);
    }
}

        Try it Yourself

⌚ In Interfaces, what are static methods?

Interface Static Methods are those methods declared in the interface with the term static. These static methods, unlike other Interface methods, contain the entire function definition, and because the definition is complete and the method is static, these methods cannot be modified or changed in the implementation class.

Static methods are useful for designing utility methods since they contain method implementation that is owned by the interface and invoked using the interface name. They cannot be overridden.

interface NewInterface {

	static void hello()
	{
		System.out.println("Hello, New Static Method Here");
	}

	void overrideMethod(String str);
}

public class InterfaceDemo implements NewInterface {

	public static void main(String[] args)
	{
		InterfaceDemo interfaceDemo = new InterfaceDemo();

		NewInterface.hello();

		interfaceDemo.overrideMethod("Hello, Override Method here");
	}


	@Override
	public void overrideMethod(String str)
	{
		System.out.println(str);
	}
}

⌚What is the definition of a predicate? What is the difference between a function and a predicate?

A pre-defined Functional Interface is referred to as a Predicate. It's in the java.util.function package. Package of predicate. It only accepts one parameter, which must be in the form described below.

Predicate

Predicate	Function
It has a Boolean return type.	It has an Object return type.
It's written in the Predicate <T> format, which only takes one parameter.	It's expressed in the format Function <T, R>, and it only takes one parameter.
It is a Functional Interface for evaluating Lambda Expressions. This can be used as a method reference target.	It also serves as a functional interface for evaluating Lambda Expressions. T stands for input type and R stands for result type in Function <T, R>. This can also be used as a Lambda Expression and Method Reference target.

⌚What is a Stream API, and how does it work? Why is the Stream API required?

The Stream API is a new Java 8 feature. It's a custom class that's used to process objects from a Collection-like source.

The Stream API is required because

It allows for aggregate operations, which simplifies the processing.
It allows you to programme in the functional style.
It has a faster processing speed. As a result, it is suitable for improved performance.
It allows for parallel processing.

⌚Which of the four built-in Java Functional Interfaces can you name?

Many interfaces have been transformed to functional interfaces starting with Java SE 1.8. @FunctionalInterface is annotated on all of these interfaces. The following are the interfaces:

Runnable: The run() function is the only method in the interface.
Comparable: The compareTo() function is the only method in this interface.
ActionListener: The actionPerformed() function is the only method in this interface.
Callable: The call() function is the only method in this interface.

⌚ What is the distinction between internal and external iteration?

The new idea of "internal iteration" was introduced in Java 8. There was only external iteration prior to Java 8. Let's look at the distinctions between internal and external iteration.

Availability: Internal iteration was introduced in JDK 8, but external iteration existed prior to that.
Iteration behavior: Internal iterator that iterates through Aggregated Object elements such as Collections and Arrays.External iterator that iterates through Aggregated Object elements.
Approach: Internal iterator is written in a declarative functional programming language.

Meanwhile, the External iterator uses an imperative style OOP approach.

⌚ What is the difference between PermGenSpace and MetaSpace?

PermGenSpace is no longer used in JDK 8 and later. The metadata was formerly stored in PermGenSpace. Metadata refers to the data that is stored about classes, such as bytecodes, names, and JIT information.Metadata for Java classes is now stored in a native heap called MetaSpace. Metaspace will automatically increase and be garbage collected by default.

The main difference between PermGenSpace and MetaSpace is that PermGenSpace has a defined size and does not grow automatically, whereas MetaSpace does not.

⌚ What is the difference between the Java 8 methods findAny() and findFirst()?

find findFirst() returns the first element of the supplied stream, while any() returns any element from the given stream.

The behaviour of findAny() is non-deterministic, but findFirst() is deterministic.

⌚ What are the features of a lambda expression?

The following are the two most important characteristics of the lambda expressions:

Lambda expressions can be supplied to another method as a parameter.
Lambda expressions can be used independently of any class.

⌚What is a stateful intermediate operation, and how does it work? Give some stateful intermediate operations examples.

Some state must be preserved to perform some intermediate activities, and these intermediate operations are referred to as stateful intermediate operations. The execution of these types of activities in parallel is difficult.

For Eg: sorted() , distinct() , limit() , skip() etc.

Data elements are not sent to subsequent steps in the pipeline until all data has been sorted for sorted() and stream data elements have been saved in temporary data structures.

⌚ What are the most significant Data and Time API packages?

Java.time.format
Java.time
1. dates
2. times
3. Instants
4. durations
5. time-zones
6. periods
Java.time.temporal
java.time.zone

⌚What are the most common terminal operations?

collect() - All elements of the stream sequence are combined into a single outcome.
reduce() - Produces a single result from the stream sequence's elements.
1. count() - The number of elements in the stream is returned.
2. min() - Returns the min element from the stream.
3. max() - Returns the stream's maximum element.
Search/Query operations
1. Short-circuiting operations, such as anyMatch(), noneMatch(), allMatch(), and so on.
2. For the match condition, it takes a Predicate as input.
3. When the result can be determined, stream processing will be ended.
Iterative operations
1. forEach() - It's beneficial to do something with each Stream element. It accepts a client.
2. forEachOrdered() - Maintaining order in parallel streams is beneficial.

⌚ What is the most convenient way to print the current date and time using Java 8's new APIs?

The current date can be obtained using the 'now' method, which is part of LocalDate, as demonstrated below:

LocalDate currentDate = LocalDate.now();
System.out.println(currentDate);

It can also be used to determine the current time:

LocalTime currentTime = LocalTime.now();
System.out.println(currentTime);

⌚ What is the purpose of stream piping?

Stream pipelining is a technique introduced in Java 8 that allows users to chain many operations together. This is based on the division of the operation into two categories:

Intermediate operations: When the stream is running, return the instance of the stream.
Terminal operations: Used to finish an operation and return the result.

Let's look at the intermediate-level questions next on this list of the best Java 8 interview questions and answers.

⌚ What is the Java 8 lambda expression code for sorting strings?

Using the lambda expression, the following code arranges strings:

//Sorting using Java 8 lambda expression

private void sortUsingJava8(List<String> names) {

    Collections.sort(names, (s1, s2) -> s1.compareTo(s2));
}

⌚ In Java 8, what are collectors?

Collectors are mostly used to combine the final result after items in a stream have been processed. They're used to return lists of items or strings of characters.

The following code demonstrates how collectors operate:

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");

List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());

System.out.println("Filtered List: " + filtered);

String mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", "));

System.out.println("Merged String: " + mergedString);

If you're interested in learning Java, Intellipaat's Java Course curriculum is a great place to start.

⌚ In Java 8, what is the simplest way to print the sum of all the numbers in a list?

To display the sum of all the numbers in a list in Java 8, use the following code:

List<Integer> numbers = Arrays.asList(5, 4, 10, 12, 87, 33, 75);
IntSummaryStatistics stats = integers.stream().mapToInt((x) −> x).summaryStatistics();
System.out.println("Sum of all numbers : " + stats.getSum());

⌚When is it most appropriate to use Java 8's Stream API?

If your Java project requires the following operations, the Stream API in Java 8 can help.

Execute database manipulations
Execute operations in a sluggish manner.
Programming in the functional style
Process data in parallel.
Take advantage of pipeline activities.
Internal iteration should be used.

⌚ What is the simplest approach to use Java 8 to locate and remove duplicate elements from a list?

Duplicate elements can be readily identified and eliminated using stream operations and a collection, followed by the Collections.toSet() method. This should get rid of all of the duplicate items in the list.

⌚ In Java 8, what is the simplest approach to convert an array to a stream?

The stream class in Java 8 may quickly convert any array into a stream. The following is an example of how to create a stream using a factory method:

String[] testarray = {"Hello", "Intellipaat", "learners"};
Stream numbers = Stream.of(testarray);
numbers.forEach(System.out::println);

Following up on this list of the best Java 8 interview questions and answers, we'll look at questions that are based on your knowledge and expertise.

🚀Conclusion

We have now reached the end of this page. With the knowledge from this page, you should be able to create your own programmes with some research, and it's in fact recommended to hone your programming skills with small projects. There is no way to cover all the information you need to be a successful programmer in one course. In fact, programming is a constant learning process, regardless of whether you are a seasoned professional developer or a newbie.

Frequently Asked Questions (FAQs)

What are Java 8 features?

Java 8 added various new features and advancements to the Java programming language. Java 8 has a few important features, including:

1. Lambda expressions: - They offer a compact approach to define anonymous functions, making the code more accessible and expressive.

- They enable the implementation of functional programming concepts in Java.

- When utilizing functional interfaces and the new stream API, lambda expressions are especially helpful.

2. Stream API: The Stream API offers a declarative and practical method for handling object collections.

- It enables functional programming operations on collections, including filtering, mapping, reducing, and sorting.

- The Stream API encourages a more functional programming approach by making it simpler to develop code that is both brief and understandable.

3. Functional Interfaces: Working with lambda expressions requires the use of functional interfaces, which are interfaces with a single abstract method.

- The 'java.util.function' package in Java 8 added a number of new functional interfaces, including 'Predicate', 'Function', 'Consumer', and 'Supplier'.

- These interfaces provide a standard set of functional interfaces for frequent use cases and simplify the use of lambda expressions.

4. Default Methods: Default methods, commonly referred to as defender methods, enable method implementations for interfaces.

- They make it possible to add new methods to interfaces that already exist without compromising backward compatibility.

- Default methods offer a mechanism to enhance interface functionality without requiring all classes that implement the interface to implement the new methods.

5. Method References: Method references give lambda expressions a clear way to refer to methods.

- They permit direct references to constructors, instance methods, or static methods without the need to explicitly write a lambda expression.

- Method references make code easier to read and write, especially when using libraries or existing APIs.

6. Optional: A container class called Optional was created to handle null values more skillfully.

- It promotes a more explicit approach to managing nullable values, lowering the possibility of null pointer errors.

- Optional offers ways to determine whether a value is present, safely retrieve the value, or provide a fallback value in the event that the value is missing.

7. Date/Time API: In the 'java.time' package, Java 8 added a new Date and Time API.

- A more thorough and adaptable way to work with dates, timings, durations, and time zones is provided by the new API.

- The earlier 'java.util.Date' and 'java.util.Calendar' classes' shortcomings and inconsistencies are addressed.

Why is Java 8 used?

Java 8 is utilized for a variety of purposes since it added important improvements and features that enhanced the programming experience and increased the Java programming language's capabilities. Here are some main explanations for why Java 8 is so popular:

1. Lambdas and Functional Programming: Lambdas, which are brief and expressive anonymous functions, were introduced in Java 8. They make it easier to use functional programming.

- Lambdas offer a reduced syntax for working with collections and creating functional interfaces, allowing developers to create shorter, more understandable code.

- Lambdas made functional programming ideas like higher-order functions, map-reduce operations, and filter operations more approachable.

- More efficient and beautiful code is now possible because to the improved functional programming capabilities, especially when working with streams, parallel processing, and asynchronous programming.

2. Stream API: The Stream API, introduced in Java 8, offers a higher-level abstraction for handling data sequences.

- Developers may use streams to quickly and expressively perform functional-style operations on collections including filtering, mapping, and reducing.

The Stream API encourages declarative and expressive programming, enabling programmers to concentrate on what needs to be done rather than how it should be done.

- Streams can also take advantage of parallel processing's advantages, making it simpler to utilize multicore processors and enhancing performance in some circumstances.

3. Default Methods in Interfaces: In Java 8, the idea of default methods in interfaces was introduced, allowing the addition of new methods to existing interfaces without compromising backward compatibility.

- By introducing method implementations, default methods give interfaces a mechanism to grow without adding further interface hierarchies.

- This feature made it possible to extend the functionality of already-existing interfaces, adding new methods to the Collection and Stream interfaces, for example.

4. Optional Class: The Optional class, introduced in Java 8, offers a type-safe method of handling null data and preventing NullPointerExceptions.

- The Optional class encourages programmers to explicitly address the lack of values, which strengthens and makes code easier to read.

- It offers techniques for carrying out actions on optional values, including filtering, mapping, and supplying default values.

5. Date and Time API: The new Date and Time API (java.time package), which replaces the outdated java.util.Date and java.util.Calendar classes, was introduced with Java 8.

- With support for time zones, durations, intervals, and more, the new Date and Time API offers a more thorough and user-friendly method of manipulating dates and times.

- Date and time operations are more consistent, immutable, and thread-safe thanks to this improvement, which also makes them more useful.

6. further Improvements: Java 8 added further capabilities and enhancements, such as the Nashorn JavaScript engine, improved annotations, improved concurrency tools, smaller embedded system profiles, and more. These improvements increased Java 8's adaptability to a larger range of use cases and increased its power and versatility.

Why Java 8 is the best?

The "best" Java version is debatable, but Java 8 is regarded as a significant turning point in the development of the Java programming language. It introduced several features and enhancements that greatly improved the language's expressiveness, productivity, and performance. Here are some explanations for why Java 8 is well-liked:

1. Lambdas and Functional Programming: One of Java 8's standout features is the addition of lambdas, which gave the Java language support for functional programming.

- Lambdas make it possible to use functional interfaces and anonymous functions, which helps developers write code that is shorter and easier to read.

- Immutability, separation of concerns, and declarative coding are encouraged by functional programming, which results in code that is simpler to understand and maintain.

- Lambdas, along with the Stream API, provide powerful functional-style operations on collections, leading to more expressive and efficient code.

2. Stream API: The Stream API, which was made available in Java 8, completely changed how data is processed in Java.

- Streams enable functional-style operations like filtering, mapping, and reducing by offering a higher level of abstraction for working with collections.

- Stream operations can be carried out sequentially or concurrently, making it simple to take advantage of multi-core processors and enhancing the efficiency of data processing tasks.

- Complex data transformations are simpler to comprehend and maintain thanks to the Stream API, which encourages more declarative and expressive code.

3. Default Methods in Interfaces: The concept of default methods in interfaces was introduced in Java 8 and allows interfaces to have method implementations.

- Default methods made it possible to implement interfaces with new methods while maintaining backward compatibility.

- This feature has been used to improve common library interfaces, like the Collection interface, without requiring the implementations of older codebases to be updated.

- Default methods offer more design and development flexibility for APIs, improving code reuse and extensibility.

4. Optional Class: The Optional class provides a more organized and secure solution for dealing with null values.

- It motivates programmers to specifically deal with the lack of values, which lowers the frequency of NullPointerExceptions.

- Developers are compelled to handle both the presence and absence of values when using Optional, which increases code reliability and clarifies intent.

- A variety of techniques, including mapping, filtering, and providing default values, are available when working with potentially absent values through the Optional class.

5. New Date and Time API: Java 8 has a brand-new Date and Time API that provides a cutting-edge and all-inclusive method of handling dates, times, and durations.

- The new API overcomes the limitations of the previous java.util.Date and java.util.Calendar classes, which were frequently regarded as error-prone and challenging to use.

- Immutable classes that are thread-safe are provided by the Date and Time API, increasing the dependability of date and time manipulation.

- Improved time zone support, date arithmetic, formatting, parsing, and other common operations are provided, resulting in clearer and easier-to-maintain code.

6. Performance Enhancements: Java 8 brought performance enhancements, especially in terms of parallel processing and stream optimizations.

- The introduction of parallel streams enables effective multi-core processor utilization, enabling quicker computation on large datasets.

- Internal improvements, like decreased synchronization overhead and improved JIT compiler optimizations, helped Java 8 achieve higher overall performance levels.

7. Backward Compatibility: Java 8 is backward compatible, which allows code created for earlier versions of Java to continue to run unaltered on Java 8. Because of this compatibility, businesses and developers can upgrade to Java 8 gradually, taking advantage of its new features while preserving compatibility with older systems.

It's important to note that the "best" version of Java depends on specific project requirements, target environment.

What is the difference between JDK 7 and 8?

The features, improvements, and enhancements included in each version are what set JDK 7 and JDK 8 apart from one another. Here are the primary differences between JDK 7 and JDK 8:

1. Lambda Expressions and Functional Programming: Functional programming in Java is made possible by the introduction of lambda expressions in JDK 8, a significant language improvement.

- Code that is more expressive and readable can be written using lambda expressions, which enable the condensed representation of anonymous functions.

- The use of functional programming ideas like closures, higher-order functions, and streamlined operations on collections is made easier by this addition.

- JDK 7, on the other hand, does not support lambda expressions, so developers have to rely on traditional approaches, like using anonymous inner classes, to achieve similar functionality.

2. Stream API and Functional Operations: - JDK 8 introduced the Stream API, which provides a higher-level abstraction for processing collections and performing functional-style operations.

- With operations like filter, map, reduce, and more, the Stream API enables programmers to write code in a more declarative and expressive manner.

- These actions can be conducted sequentially or in parallel, exploiting multicore computers for greater speed.

- JDK 7 does not provide the Stream API, therefore developers have to revert to traditional loops and iteration methods for collection processing.

3. Default and Static Methods in Interfaces: The inclusion of default and static methods to interfaces was made possible by JDK 8, which was a big change.

- Default methods provide a way to add new methods to existing interfaces without breaking the implementations of classes that implement those interfaces.

- The addition of utility methods in interfaces that may be accessed directly by the interface name is possible thanks to static methods.

- This enhancement promotes better code reuse and provides a mechanism for evolving interfaces without disrupting existing codebases.

- JDK 7 does not support default and static methods in interfaces.

4. Date and Time API: - JDK 8 introduced a new Date and Time API (java.time package) to address the limitations and complexities of the old java.util.Date and java.util.Calendar classes.

- The new Date and Time API provides a more comprehensive and intuitive approach to handling dates, times, time zones, durations, and periods.

- It offers improved consistency, immutability, and thread-safety, making date and time operations more reliable and easier to work with.

- The java.util.Date and java.util.Calendar classes, which are known to have design flaws and are more error-prone, are responsible for providing date and time functionality in JDK 7.

5. Improved Performance and JVM Enhancements: - JDK 8 introduced several performance improvements and JVM enhancements compared to JDK 7.

- JDK 8 includes improvements to the Java Virtual Machine (JVM), such as the addition of the Metaspace memory area, the use of the invokedynamic instruction to improve the performance of dynamic languages, and improved Garbage Collection algorithms. These enhancements result in better overall performance, lower memory usage, and more effective Java application execution.

6. Other Features and Enhancements: - JDK 8 introduced other features and enhancements such as the Optional class for handling null values, the Nashorn JavaScript engine, improved security and cryptography support, new APIs for concurrency and parallelism, enhanced annotations, and more.

- These changes aimed to increase developer efficiency, code maintainability, and performance of the application.

What is the difference between Java 8 and Java 9 features?

The features and improvements added in each version are what set Java 8 and Java 9 apart from one another. The following are the main variations between Java 8 and Java 9:

1. Module System (Project Jigsaw):

- Java 9 introduced a significant feature referred to as the Module System.

- The Module System provides a way to encapsulate Java code into modules, enabling better modularity and strong encapsulation of dependencies.

- Modules define explicit dependencies and offer better control over access to internal APIs, enhancing security and maintainability.

- With the help of this capability, programmers may build libraries and applications that are modular, which enhances code structure and makes systems more scalable and manageable.

- There is no Module System in Java 8.

2. Java Platform Module System (JPMS):

- A key element of Java 9's Module System is the Java Platform Module System (JPMS).

- JPMS offers a new format for Java runtime images made up of modules, enabling improved runtime execution and deployment.

- It introduces the idea of module descriptors, which explicitly declare services, exported packages, and module dependencies (module-info.java).

- The JPMS offers a standardized method to manage modules both at compile-time and runtime, which makes it easier to develop and deploy modular applications.

- Java 8 does not feature the Java Platform Module System.

3. REPL (JShell):

- JShell, a Read-Eval-Print Loop (REPL) tool that offers an interactive environment for evaluating Java code snippets, was introduced with Java 9.

- Without having to write entire programs, developers can experiment, test short bits of code, and investigate APIs using JShell.

- JShell delivers real-time feedback, enables quick prototyping, and promotes learning.

- This feature makes it easier and more interactive for developers to work with Java code, which increases developer productivity.

- Java 8 does not include JShell.

4. Reactive Streams API:

- The Reactive Streams API was standardized in Java 9 and provides non-blocking back pressure for asynchronous stream processing.

- Interoperability across various reactive libraries is made possible by the Reactive Streams API, which establishes a standard set of interfaces, classes, and protocols for reactive programming.

- It promotes responsiveness and scalability by making it easier to create reactive systems that can manage massive amounts of data while maintaining flow control.

- The Reactive Streams API aims to simplify the development of reactive applications and integrate with other reactive libraries.

- The Reactive Streams API is absent from Java 8.

5. Improved Stream API:

- Although the Stream API was first introduced in Java 8, Java 9 offered a number of improvements to enhance its performance and usability.

- 'takeWhile()', 'dropWhile()', and 'iterate()' are three new methods that Java 9 adds to the Stream API, allowing for more flexible stream operations.

- These improvements offer more effective and succinct ways to communicate intricate data processing pipelines.

- Java 9 also introduced improvements to the performance and efficiency of the Stream API.

- Java 8 includes the Stream API but lacks some of the enhancements present in Java 9.

6. HTTP/2 Client API:

- Java 9 introduced a new HTTP/2 Client API as a replacement for the existing HttpURLConnection API.

- Consuming HTTP/2-based services is made easier and more efficient by the HTTP/2 Client API.

- It supports the HTTP/2 protocol's multiplexing, server push, and enhanced performance features.

- The API offers a fluent and intuitive programming model for making HTTP requests and handling responses.

- There is no HTTP/2 Client API in Java 8.

7. Other Features and Enhancements:

- Java 9 introduced other features and enhancements, such as the new Process API for controlling and managing operating system processes, enhanced security, better multi-release JAR support, compact strings to save memory, and performance enhancements in a variety of areas.

- These changes sought to improve developer efficiency,code quality, security, and performance.

What is lambda expression in java8?

The Java language's expressiveness and conciseness were improved with the introduction of lambda expressions in Java 8. You can treat code as data by using an anonymous function called a lambda expression. It enables Java functional programming by giving a clear way to represent a block of code as an object. A thorough description of lambda expressions in Java 8 is provided below:

1. Anonymous Functions:

- A lambda expression can be thought of as an anonymous function because it doesn't have a name associated with it.

- It contains a section of code that can be saved in data structures, assigned to variables, or passed around as a parameter.

- Code is treated as data by lambda expressions, enabling runtime manipulation and execution.

2. Syntax:

- A lambda expression has a three-part syntax: a parameter list, an arrow token ("->"), and a body.

- The parameter list defines the input parameters of the lambda expression.

- The parameter list and body are divided by the arrow token.

- The code that will run when the lambda expression is called is contained in the body.

3. Functional Interfaces:

- Lambda expressions and functional interfaces are frequently used together.

- An interface that only has one abstract method is said to be functional.

- An efficient way to implement the abstract method of a functional interface is through lambda expressions.

- You can make an instance of a functional interface by giving it a lambda expression.

4. Simplified Code:

- Lambda expressions minimize the need to write anonymous inner classes or separate classes for straightforward behaviors, which leads to simpler code overall.

- They offer a clearer and easier-to-read manner to convey functionality, particularly for simple, one-purpose methods.

- Rather than writing the boilerplate code necessary for conventional methods, lambda expressions let you concentrate on the logic you want to express.

5. Capturing Variables:

- Lambda expressions have access to variables in the scope in which they are used.

- The term "captured" variables refers to these variables.

- Variables whose values do not change after initialization are referred to as final or effectively final variables and can be accessed by lambda expressions.

- The captured variables function as though they were declared inside the lambda expression's body and are accessible there.

6. Examples:

- To demonstrate how lambda expressions are used in Java 8, here are a few examples:

// Example 1: Lambda expression with no parameters
Runnable runnable = () -> System.out.println("Hello, world!");
runnable.run();

// Example 2: Lambda expression with parameters
Comparator< String > comparator = (a, b) -> a.length() - b.length();
int result = comparator.compare("apple", "banana");

// Example 3: Lambda expression with multiple statements in the body
Consumer< Integer > printer = (n) -> {
    for (int i = 0; i < n; i++) {
        System.out.println(i);
    }
};
printer.accept(5);

- In Example 1, a lambda expression is given to a 'Runnable' interface, signifying an executable chunk of code.

- Example 2 shows how to use a lambda expression to provide specific comparison logic for strings based on their lengths when it is attached to a "Comparator" interface.

- Example 3 demonstrates an assignment of a lambda expression to a "Consumer" interface, defining a block of code that accepts an integer and prints integers up to that value.

The expressiveness and adaptability of the Java language have been substantially enhanced by lambda expressions. They make code more legible and compact while enabling functional programming techniques. When combined with functional interfaces, lambda expressions offer a technique to create more modular, adaptable, and reuseable code.

Why Java 8 is better than Java 11?

Depending on the particular requirements, the context of the project, and personal preferences, Java 8 may be preferable to Java 11 or vice versa. Both releases significantly improved the Java platform and language. Consider the following factors when comparing Java 8 to Java 11:

1. New Features and Improvements: Java 8 added a number of significant features, such as lambda expressions, the Stream API, default methods in interfaces, and the new Date and Time API.

These features improved collection processing, improved date and time manipulation, and functional programming capabilities.

- The HttpClient API, improvements to the Java Platform Module System (JPMS), improved garbage collection, and the introduction of the GraalVM compiler were among the new features introduced in Java 11, in contrast.

- Java 11 prioritizes modularity, performance, and enhanced APIs while Java 8 concentrated on functional programming and streamlining code.

2. Performance and Security: Java 11 added improvements like the Low-Pause-Time Garbage Collector (Epsilon), which minimizes the negative effects of garbage collection on application performance.

- For further security, it also featured the cryptographic algorithms ChaCha20 and Poly1305.

- It's important to remember that Java is constantly being improved in terms of efficiency and security, and that versions after Java 11 have brought even more advancements in these areas.

3. Language and API Improvements: Java 8 and Java 11 both brought about significant language and API upgrades.

- Java 8 revolutionized the way code is written and collections are processed by introducing lambda expressions, functional interfaces, and the Stream API.

- Java 11 introduced features like the lambda parameter local-variable syntax, allowing for shorter lambda expressions.

- The HttpClient API was also introduced, offering a more advanced and effective way to use HTTP/HTTPS services.

- These improvements in both versions were made in an effort to improve performance, code quality, and developer productivity.

4. Support for Tooling and the Ecosystem: Java 11 introduced Long-Term Support (LTS) status, which means it will receive updates and bug fixes for a longer period of time compared to non-LTS releases.

- It is important for enterprise applications and organizations that prefer stability and long-term support to consider using Java 11 or subsequent LTS releases.

- In addition, over time, tooling and ecosystem support for more recent Java versions have improved, with libraries, build tools, and IDEs accommodating the newest language features and improvements.

5. Compatibility and Migration: Since Java 8's release, it has received a lot of adoption, and many active projects and codebases continue to use Java 8 as their foundation.

- It may take more work to upgrade from Java 8 to Java 11 or a newer version because it involves determining compatibility, updating dependencies, and taking care of potential code changes brought on by deprecated APIs or language semantics.

- However, more recent Java releases frequently include enhanced speed, security, and features that can be useful for ongoing maintenance and future development.

Why abstract class is required in Java 8?

With the addition of default methods in Java 8, interfaces gained more functionality and in some cases replaced the need for abstract classes. However, abstract classes still serve an important purpose in Java 8 and beyond. Here are some reasons why abstract classes are still required in Java 8:

1. Defining Common Functionality: Abstract classes let you define attributes and common functionality that can be shared by a number of subclasses.

- It is possible for related classes to share code implementation through the use of abstract classes, which can contain both abstract and non-abstract methods.

- This encourages code reuse and reduces the need for duplicate code.

2. Partial Implementation: Abstract classes are capable of having abstract methods that are declared but not used by the abstract class itself.

- Subclasses that derive from abstract classes must implement these abstract methods in order to fulfill the subclass's contractual obligations.

- Subclasses are in charge of adding the missing behavior, allowing abstract classes to give partial implementation.

3. Encapsulation and Hiding Details: - Abstract classes can encapsulate and hide internal implementation details.

- The abstract class can mandate that subclasses provide their own implementation by designating specific methods as abstract, hiding the implementation specifics from outside code.

- This promotes encapsulation and allows for better code organization and maintainability.

4. Compatibility with Code Written Before Java 8: Abstract classes are compatible with code bases written before Java 8 that were built on the foundation of abstract classes.

- Because so many current codebases and libraries rely on abstract classes, a complete migration to interfaces might not be possible or practical.

- Such codebases can be supported and extended using abstract classes without compromising compatibility.

5. Adding New Classes to an Existing Class Hierarchy: Abstract classes can provide as a foundation for new classes that add to an existing class hierarchy.

- A class in Java can implement multiple interfaces but can only directly extend one superclass.

- You can build an intermediate class in the hierarchy that offers common functionality using abstract classes, and you can then have many subclasses extend that abstract class. This supports better code organization and enables more flexible class hierarchies.

6. Limitations of Default Methods: Default methods in interfaces offer a way to add new methods to existing interfaces without compromising compatibility, but they also have some restrictions.

- Default methods are unable to access or hold state, as well as non-static fields, of the implementing class.

- Abstract classes, on the other hand, can hold state and allow access to its fields and functions to subclasses.

- Abstract classes enable a more conventional method of defining classes with shared state and behavior.

Which JDK is most used?

One of the most popular Java Development Kit (JDK) versions as of the knowledge cutoff in September 2021 was Java SE 8 (JDK 8). It's crucial to remember that JDK usage and acceptance can fluctuate over time and depend on a variety of elements, including project requirements, industry norms, and the Java ecosystem. Here is a summary of JDK usage and acceptance:

1. JDK 8 (Java SE 8):

- Lambda expressions, the Stream API, default methods in interfaces, and the new Date and Time API were some of the important additions that JDK 8 introduced when it was launched in March 2014.

- Many organizations and projects embraced JDK 8 because of its long-term support (LTS) status and kept using it even after subsequent JDK versions were released.

- JDK 8 is a well-liked option for enterprise applications because of its reliability, maturity, and backward compatibility, which guarantees compatibility with current codebases and libraries.

2. JDK 11 (Java SE 11):

- JDK 11, the following long-term support (LTS) version after JDK 8, was released in September 2018. This represented another significant milestone.

- JDK 11 provided changes to the Java Platform Module System (JPMS), the HTTP Client API, and improved security and efficiency.

- JDK 11 was a desirable option because of its LTS designation for programs that needed reliability and long-term support, especially in enterprise contexts.

3. Java SE 15+ (JDK 15+): Oracle switched to a new six-month release cycle for JDK versions after JDK 11, which resulted in the rapid introduction of new features and improvements.

- Features like text blocks, record classes, pattern matching, foreign function and memory API, and more were added in JDK versions 15, 16, and later releases.

- These versions brought intriguing language and API improvements, but how widely they are used will rely on things like the project's particular requirements, the accessibility of libraries and frameworks, and the compatibility of pre-existing codebases.

4. Additional factors: - The choice of JDK version can be influenced by industry-specific needs, such as adherence to a particular standard or legislation.

- Older JDK versions could be needed for legacy systems and applications, necessitating their continued use and support.

- The availability of libraries and frameworks, community support, and people's perceptions of stability and dependability all contribute to how popular different JDK versions are.

It's important to note that Java places a high priority on backward compatibility, enabling programs created for earlier JDK releases to operate without major adjustments on more recent releases. When switching to a new JDK version, compatibility testing and considerations are still required.

Overall, the most popular JDK version might change depending on particular needs, business trends, and developer and organization preferences. To make an informed choice based on the unique requirements of the project, it is crucial to assess the features, performance, long-term maintenance, and ecosystem support offered by various JDK versions.

What is the Collectors API?

Java 8 included the Collectors API feature, which offers a number of preset collectors to make it easier to gather and summarize data from streams. By providing a more direct and expressive mechanism to carry out typical data collecting activities, it improves the functionality of the Stream API. Data operations including grouping, splitting, summarizing, and aggregating can be carried out using a variety of methods provided by the Collectors API. Here is a thorough overview of the Collectors API's main characteristics:

1. Collectors: In Java 8, there are numerous static methods that return various collectors in the Collectors class.

The 'collect()' method of the Stream API can be used in conjunction with collectors to gather and process stream components.

- Collecting items into collections, arranging elements according to specific criteria, summarizing data, and other routine tasks are all made simple by collectors.

2. Common Operations: The Collectors API provides collectors for typical activities like gathering elements into a List, Set, or Map.

- As an illustration, the collector 'toList()' gathers the stream elements into a List, whereas 'toSet()' gathers them into a Set.

- The "toMap()" collector uses key and value mapping techniques to compile elements into a Map.

- These collectors make it easier to gather data and arrange it into widely-used data structures.

3. Data grouping and partitioning: The Collectors API offers collectors for performing these operations based on predetermined criteria.

- The 'groupingBy()' collector organizes elements according to a classifier function, generating a Map whose keys denote the groups and values denote the elements that are a part of each group.

- The "partitioningBy()" collector creates a Map with two keys: "true" for elements that satisfy the predicate and "false" for the remainder. It splits elements into two groups based on the predicate.

- Collectors that group and partition data provide effective data organization and condition-based analysis.

4. Summarizing Data: The Collectors API has collectors that can calculate sums, averages, maximum and minimum values, and other data summaries.

- The collector functions "summarizingInt()," "summarizingLong()," and "summarizingDouble()" offer statistical summaries of elements in a stream, including count, sum, average, maximum, and lowest values. Without having to create original code, these collectors offer a practical solution to get summary statistics from data.

5. Custom Collectors: Using the 'Collector' interface or by combining different collectors, the Collectors API enables the development of custom collectors.

- Developers can specify unique data gathering methods with custom collectors that are not supported by the preset collectors.

- Custom collectors offer the flexibility and extensibility needed to modify the Collectors API to meet the needs of particular applications.

What are disadvantages of Java 8?

Despite the fact that Java 8 has improved the Java language and platform, it's vital to take some of its drawbacks into account. Here are a couple possible Java 8 negatives:

1. Compatibility Issues: One of the difficulties in implementing Java 8 is its compatibility with earlier Java versions.

- To ensure compatibility with Java 8, codebases created using earlier versions of Java may need to be modified and tested.

- In addition, third-party frameworks and libraries might need to be upgraded to support Java 8, which could cause compatibility problems and necessitate project revisions.

2. Learning Curve: For developers who are unfamiliar with the ideas of functional programming, Java 8 introduced a number of new features and language structures, such as lambda expressions and the Stream API, which may have a steep learning curve. Existing Java developers may experience a learning curve as it may take some time for them to comprehend and apply these new functionalities efficiently.

3. Migration Effort: - Moving codebases from earlier Java versions to Java 8 can be a difficult undertaking, especially for big and complicated projects.

- To conform to the functional programming paradigm, the introduction of lambda expressions and other new language features may necessitate substantial code revisions. To ensure the stability and accuracy of the application, this migration effort may include updating libraries and frameworks, reworking existing code, and extensive testing.

4. Limited IDE Support: Although Java 8 has been around for a while, certain older Integrated Development Environments (IDEs) may only partially or not at all support the new language features that Java 8 introduced. Because of this, it may be difficult for developers to fully take advantage of Java 8 features like code auto-completion and refactoring support in some IDEs.

5. speed Considerations: - Although Java 8 brought about a number of speed improvements, the use of some features, such as streams and lambda expressions, may result in a modest performance overhead when compared to more conventional imperative programming structures.

- With its focus on immutability and higher-order functions, Java 8's functional programming approach might call for more object constructions and method invocations than usual, which could have an effect on performance in some circumstances.

- The advantages of better code readability and maintainability can exceed the normally minimal performance impact.

6. Limited Backward Compatibility: Despite maintaining backward compatibility with prior Java versions, several new features, such as lambda expressions and default methods in interfaces, are incompatible with earlier Java releases.

- Projects that must remain compatible with earlier Java versions might encounter difficulties when attempting to use these new language features, which would limit Java 8's adoption and advantages in those circumstances.

It's important to note that many of these drawbacks apply to any significant version of a programming language or platform. The advantages and improvements brought about by Java 8 frequently surpass the difficulties, and these drawbacks can be successfully overcome with good planning, testing, and implementation techniques. Since Java 8 has been replaced by newer iterations of the language, some of these drawbacks may have been fixed.

What is the Nashorn JavaScript engine?

One of the most important new features in Java 8 is the Nashorn JavaScript engine. It gives the Java Virtual Machine (JVM) a high-performance JavaScript runtime environment. Nashorn bridges the gap between the Java and JavaScript programming languages by enabling developers to execute JavaScript code directly in Java applications.

A thorough overview of the Nashorn JavaScript engine is provided below:

1. JavaScript and Java integration: Nashorn makes it possible to seamlessly combine JavaScript and Java code in a single application.

- It enables interoperability between the two programming languages by allowing developers to call Java code from JavaScript and vice versa.

- This integration offers the freedom to use the advantages of both languages for particular tasks, utilizing both JavaScript code and already-existing Java tools and frameworks.

2. Improved Performance: Nashorn is made to offer the JVM with high-performance JavaScript code execution.

- To attain effective execution speeds, it makes use of just-in-time (JIT) compilation and other optimization techniques.

- Nashorn is a practical choice in situations where running JavaScript code in a Java environment is necessary because of its performance gains.

3. Support for command-line tools and scripting: Nashorn comes with a command-line tool called "jjs" that lets you run JavaScript files straight from the command line, just like you would with scripts written in other scripting languages. With the help of this command-line tool, it is simple to run JavaScript code without the requirement for an additional JavaScript runtime environment.

The use of JavaScript for scripting activities within Java applications is made possible by Nashorn's support for scripting, making it practical for automation, build scripts, and other scripting scenarios.

4. Embedding JavaScript in Java Applications: Nashorn enables dynamic behavior and extensibility by allowing developers to embed JavaScript code within Java applications.

- Direct loading, execution, and interaction with JavaScript code is possible.

- When developers wish to give users of their Java applications customisation or scripting abilities, this capability is helpful.

5. Support for ECMAScript 5.1:

ECMAScript 5.1, a widely used version of the JavaScript language specification, is supported by Nashorn.

- Nashorn can execute a broad variety of JavaScript code, including code that depends on particular language features and behaviors specified in the specification, thanks to its ECMAScript 5.1 compatibility.

6. Java 11's restrictions and deprecation: It's significant to note that the Nashorn JavaScript engine has been deprecated in Java 11 and later versions. Although it is still accessible in Java 8, it is no longer being actively updated or improved. The choice to use external JavaScript runtimes, such GraalVM's JavaScript engine, and concentrate efforts on other Java platform components led to the retirement of Nashorn in Java 11.

TEST YOUR KNOWLEDGE!

1.Which of the following statements about Java8 is correct?

1. To figure out dependencies, new compiler tools and utilities, such as 'jdeps,' have been added.
2. A new stream API has been implemented to help with pipeline processing.
3. Improved date and time API has been introduced. 4. All of the above

2.Which of the following features isn't included in Java 8?

1. Stream API
2. Serialization
3. Spliterator
4. Lambda Expression

3. What type of return does a lambda expression have?

1. String
2. Object
3. void
4. Function

4. What are the two types of Streams that Java 8 provides?

1. sequential and parallel
2. sequential and random
3. parallel and random
4. random and synchronized

5.In a class, how will you invoke a static method of an interface?

1. Using the super keyword in conjunction with the interface name.
2. Using name of the interface.
3. Both of the above.
4. None of the above.

6.In java8, which of the following statements about Optional is correct?

1. A container object is optional and is used to hold not-null things.
2.To represent null with no value, an optional object is utilised.
3. Both of the above.
4. None of the above.

7. Which feature of Java 8 allows us to establish a work-stealing thread pool that uses all of the processors available at the target?

1. workPool
2. threadPool
3. newWorkStealingPool
4. workThreadPool

8. In the context of Functional Interface, what does SAM stand for?

1.Single Abstract Method
2. Single Ambivalue Method
3. Simple Active Markup
4. Simple Abstract Markup

9. Which package in Java 8 contains the newly added Streams API:

1.java.io.streams
2. java.io.stream
3. java.util.stream
4. java.util.streams

10. How sorting speed has been improved significantly on multi-core machines by using

1. Arrays.parallelSort
2. Arrays.sort
3. Collection.parallelSort
4. Arrays.sortParallelly

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OOPs Concepts

⌚ What New Features Did Java 8 Include?

⌚What are functional or SAM interfaces?

⌚ What Is a Default Method, and When Should It Be Used?

⌚ What are the significant advantages of Java 8?

⌚ What are Lambda Expressions in Java?

⌚ Describe some of the Standard Library's functional interfaces.

⌚Describe the rules that users should adhere to when utilising Java Functional Interfaces.

⌚Describe in brief about the method references in Java?

⌚Explain the Lambda Expression's Syntax and Characteristics.

⌚ what is optional class in java? How can we use it?

⌚ What Exactly Is a Stream? What Sets It Apart From a Collection?

⌚ What are the distinctions between intermediate and terminal operations?

⌚ What's the Difference Between Map and FlatMap Streaming?

⌚ In Java 8, what is Stream Pipelining?

⌚What are the benefits of utilising the Optional class over other classes?

⌚ What are the different types of data objects that a Stream can handle?

⌚Which intermediate operations are the most typically used?

⌚In Java8, what is Nashorn?

⌚ Tell Us About Java 8's New Date and Time API

⌚ In Java SE 8, what do you mean by Streams?

⌚ What are the two types of common Java Streams operations?

⌚ What's the difference between Streams and Collections?

⌚ What are some of the most common Terminal operations in the Java programming language?

⌚ What is the best scenario for a user to use the Java Streams API?

⌚ What is the distinction between an Iterator and a Spliterator?

⌚ What is the difference between Function and Predicate in Java 8 and how are they similar?

⌚What problems do the old Date and Time APIs have? Can you describe the new Java 8 Date and Time APIs?

⌚ What's the Difference Between Map and FlatMap Streaming?

⌚In Java 8, what is MetaSpace?

⌚ In Java 8, what is the StringJoiner class? How can we use the StringJoiner Class to join several Strings?

⌚ Create a Java 8 programme that adds a prefix and suffix to a String.

⌚ In Interfaces, what are static methods?

⌚What is the definition of a predicate? What is the difference between a function and a predicate?

⌚What is a Stream API, and how does it work? Why is the Stream API required?

⌚Which of the four built-in Java Functional Interfaces can you name?

⌚ What is the distinction between internal and external iteration?

⌚ What is the difference between PermGenSpace and MetaSpace?

⌚ What is the difference between the Java 8 methods findAny() and findFirst()?

⌚ What are the features of a lambda expression?

⌚What is a stateful intermediate operation, and how does it work? Give some stateful intermediate operations examples.

⌚ What are the most significant Data and Time API packages?

⌚What are the most common terminal operations?

⌚ What is the most convenient way to print the current date and time using Java 8's new APIs?

⌚ What is the purpose of stream piping?

⌚ What is the Java 8 lambda expression code for sorting strings?

⌚ In Java 8, what are collectors?

⌚ In Java 8, what is the simplest way to print the sum of all the numbers in a list?

⌚When is it most appropriate to use Java 8's Stream API?

⌚ What is the simplest approach to use Java 8 to locate and remove duplicate elements from a list?

⌚ In Java 8, what is the simplest approach to convert an array to a stream?

🚀Conclusion

Frequently Asked Questions (FAQs)

TEST YOUR KNOWLEDGE!

1.Which of the following statements about Java8 is correct?

2.Which of the following features isn't included in Java 8?

3. What type of return does a lambda expression have?

4. What are the two types of Streams that Java 8 provides?

5.In a class, how will you invoke a static method of an interface?

6.In java8, which of the following statements about Optional is correct?

7. Which feature of Java 8 allows us to establish a work-stealing thread pool that uses all of the processors available at the target?

8. In the context of Functional Interface, what does SAM stand for?

9. Which package in Java 8 contains the newly added Streams API:

10. How sorting speed has been improved significantly on multi-core machines by using

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