Java 8 Function interface

Posted By : Lokesh Babu Sharma | 09-Dec-2020

INTRODUCTION

 

In this blog, we try to know about the Function interface. The function is a functional interface. It takes an argument of Type T and return object of Type R. The type of argument and the returning object can be different.

 

  • T: the type of the input argument
  • R: the return type of the function

 

@FunctionalInterface
public interface Function<T, R> {

      R apply(T t);

}

 

METHOD

there are four methods presented in the Function interface.

1. apply()

2. applyThen()

3. compose()

4. identity()

 

Also Read: Improving User Experiences With Progressive Web App 

 

apply()

This method applies to only the given argument and returns the result of type R.

Syntax : R apply( T t )

 

import java.util.function.Function;

public class Example {

    public static void main(String[] args) {

        Function<String, Integer> func = x -> x.length();

        Integer apply = func.apply("Hello");

        System.out.println(apply); //prints 5

    }

}

 

applyThen()

This is a chain method of Function interface. First andThen method's argument function will be executed and after that apply executes.

Syntax : <V> Function<T, V> andThen(Function<? super R, ? extends V> after)

Where V is the type of output of the after function, and of the composed function.

 

import java.util.function.Function;

public class Example {

    public static void main(String[] args) {

        Function<String, Integer> func = x -> x.length();

        Function<Integer, Integer> func2 = x -> x * 2;

        Integer result = func.andThen(func2).apply("Hello");

        System.out.println(result); // prints 10

    }

}

 

compose()

This method is the wise versa of applythen() method.

Syntax : <V> Function<V, R> compose(Function<? super V, ? extends T> before)

Where V is the type of output of the after function, and of the composed function.

 

import java.util.function.Function; 
  
public class Example { 
    public static void main(String args[]) 
    { 
        Function<Integer, Double> half = a -> a / 2.0; 
    
        half = half.compose(a -> 3 * a); 
    
      System.out.println(half.apply(5)); //prints 7.5 
    } 
} 

 

identity() 

This method of Function interface returns a function that returns its only argument.

Syntax : static <T> Function<T, T> identity()

 

import java.util.function.Function; 
  
public class Example { 
    public static void main(String args[]) 
    { 
        Function i = Function.identity(); 
  
        System.out.println(i); // prints java.util.function.Function$$Lambda$1/250421012@119d7047
    } 
} 

 

CONCLUSION

The above function interface is present in the Java 8 API. We can use these as lambda expressions.

 

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About Author

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Lokesh Babu Sharma

Lokesh is in backend team. He Believes in smart work, He is good in programming. He loves to play with codes.He has expertise in Java.

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