What is Functional Interface In Java ?

Functional Interface :

It belongs to java.util.function; package functional interface is defined as an interface with exactly one abstract method ,some functional interfaces are :

1. Function<T,R> - takes an object of type T and returns R.
2. Supplier<T> - just returns an object of type T.
3. Predicate<T> - returns a boolean value based on input of type T.
4. Consumer<T> - performs an action with given object of type T.
5. BiFunction - like Function but with two parameters.
6. BiConsumer - like Consumer but with two parameters. 

It also have some  interfaces for primitive data type :

1. IntConsumer
2. IntFunction<R>
3. IntPredicate
4. IntSupplier 

Example Showing Functional Interface:

import java.util.Arrays;

import java.util.List;

import java.util.function.Consumer;

import java.util.function.Predicate;

public class FunctionalInterfaces {

public static void main(String[] args) {

List<Integer> list = Arrays.asList(1,2,5,8,3,6,9);

System.out.println("USE OF CUNSUMER INTERFACE TO TRAVERSE LIST");

list.forEach(new Consumer<Integer>() {

@Override

public void accept(Integer t) {

System.out.println(t);

}

});

System.out.println("\nEVEN NUMBERS FROM LIST");

Predicate<Integer> predicate = n-> n%2 == 0;

list.forEach(new Consumer<Integer>() {

@Override

public void accept(Integer t) {

if(predicate.test(t)){

System.out.println(t);

}

}

});

System.out.println("\nODD NUMBERS FROM LIST");

Predicate<Integer> oddPre = n-> n%2 != 0;

list.forEach(new Consumer<Integer>() {

@Override

public void accept(Integer t) {

if(oddPre.test(t)){

System.out.println(t);

}

}

});

System.out.println("\nNUMBERS GREATER THAN 3 IN LIST");

Predicate<Integer> pre1 = n -> n>3;

list.forEach(new Consumer<Integer>() {

@Override

public void accept(Integer t) {

if(pre1.test(t)){

System.out.println(t);

}

}

});

}

}

Program Output :

USE OF CUNSUMER INTERFACE TO TRAVERSE LIST

1

2

5

8

3

6

9

EVEN NUMBERS FROM LIST

2

8

6

ODD NUMBERS FROM LIST

1

5

3

9

NUMBERS GREATER THAN 3 IN LIST

5

8

6

9

                                                   

Blog Author - Pushkar Khosla,
Software Developer by Profession with 3.0 Yrs of Experience , through this blog i'am sharing my industrial Java Knowledge to entire world. For any question or query any one can comment below or mail me at pushkar.itsitm52@gmail.com.

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