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Java 8 вопросы и ответы для интервью

Test your skills through the online practice test: Java 8 Quiz Online Practice Test

Связанные сравнения

Java 7 vs Java 8	Java 8 vs Java 9

Вопрос 1. What are new features which got introduced in Java 8?

There are lots of new features which were added in Java 8. Here is the list of important features:

Lambda Expression
Stream API
Default methods in the interface
Functional Interface
Optional
Method references
Date API
Nashorn, JavaScript Engine

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Вопрос 2. What are main advantages of using Java 8?

There are the main advantages of using Java 8:

More compact code
Less boiler plate code
More readable and reusable code
More testable code
Parallel operations

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Вопрос 3. What is lambda expression?

Lambda expression is anonymous function which have set of parameters and a lambda (->) and a function body. You can call it function without name.

Structure of Lambda Expressions:

(Argument List) ->{expression;} or

(Argument List) ->{statements;}

For instance, the Runnable interface is a functional interface, so instead of:

Thread thread = new Thread(new Runnable() {

public void run() {

System.out.println("Hello World!");

}

});

Using Lambda you can simply do the following:

Thread thread = new Thread(() -> System.out.println("Hello World!"));

Functional interfaces are usually annotated with the @FunctionalInterface annotation - which is informative and does not affect the semantics.

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Вопрос 4. Can you explain the syntax of Lambda expression?

So we can divide structure of Lambda expression to three parts:

Arguments
Array Token
Statements

1. Argument list or parameters

Lambda expression can have zero or more arguments. First part before '->' is called as argument list or parameters.

()->{System.out.println("Hello")}; //Without argument, will print hello

(int a)->{System.out.println(a)} //; One argument, will print value of a

(int a,int b)-> {a+b};//two argument, will return sum of these two integers

2. Array token (->)

3. Body

Body can have expression or statements.
If there is only one statement in body, curly brace is not needed and return type of the anonymous function is same as of body expression.
If there are more than one statements, then it should be in curly braces and return type of anonymous function is same as value return from code block, void if nothing is returned.

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Вопрос 5. What are functional interfaces?

Functional interfaces are those interfaces which can have only one abstract method. It can have static method, default methods or can override Objectâ€™s class methods.
There are many functional interfaces already present in java such as Comparable, Runnable.
As we have only one method in Runnable, hence it is considered as functional interface.

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