Lambda Expressions in Java

    Lambda expression is a new and important feature of Java which was included in Java SE 8. It provides a clear and concise way to represent one method interface using an expression. It is very useful in collection library. It helps to iterate, filter and extract data from collection.

The Lambda expression is used to provide the implementation of an interface which has functional interface. It saves a lot of code. In case of lambda expression, we don't need to define the method again for providing the implementation. Here, we just write the implementation code.

(argument-list) -> {body}  

Java lambda expression is consisted of three components.

1) Argument-list: It can be empty or non-empty as well.

2) Arrow-token: It is used to link arguments-list and body of expression.

3) Body: It contains expressions and statements for lambda expression.

Without Lambda Expression

interface Drawable{

public void draw();

}

public class LambdaExpressionExample {

public static void main(String[] args) {

int width=10;

//without lambda, Drawable implementation using anonymous class

Drawable d=new Drawable(){

public void draw(){System.out.println("Drawing "+width);}

};

d.draw();

}

}

Lambda Expression Example

@FunctionalInterface //It is optional

interface Drawable{

public void draw();

}

public class LambdaExpressionExample2 {

public static void main(String[] args) {

int width=10;

//with lambda

Drawable d2=()->{

System.out.println("Drawing "+width);

};

d2.draw();

}

}

If there is only one statement, you may or may not use return keyword. You must use return keyword when lambda expression contains multiple statements.

interface Addable{

int add(int a,int b);

}

public class LambdaExpressionExample6 {

public static void main(String[] args) {

// Lambda expression without return keyword.

Addable ad1=(a,b)->(a+b);

System.out.println(ad1.add(10,20));

// Lambda expression with return keyword.

Addable ad2=(int a,int b)->{

return (a+b);

};

System.out.println(ad2.add(100,200));

}

}