function identity () or identity method

 

Function.identity() Overview :

It is a static method in the  interface. It returns a function that accepts an input and returns the same input without any modifications. Essentially, it is a "no-op" function.

The  method in Java 8 is part of the functional programming features introduced with the java.util.function package. It is a static method in the  interface and is often used in scenarios where you need a function that simply returns its input, without making any changes or transformations.

Definition:

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

Returns a function that always returns its input argument.

Type Parameters:

T - the type of the input and output objects to the function

Returns:

a function that always returns its input argument

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

This method returns a function that always returns its input argument.

Purpose:

1. It is a convenience method used when you don't want to apply any transformation to the input.
2. Often used in streams or other functional operations where a function is required but no transformation is needed.

Key Characteristics:

• Useful as a default or placeholder function.
• The returned function is a "no-op" (no operation).

Why should we use it?

1. No Transformation Needed: It's useful when you need a function but don't want to apply any transformation to the input.
2. Code Simplification: Instead of writing a lambda expression like , you can use .
3. Default/Placeholder Function: Acts as a default mapper or identity function in various operations

Example1 :

import java.util.*;

import java.util.function.Function;

import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("apple", "banana", "cherry");

        Map<String, String> map = list.stream()

            .collect(Collectors.toMap(Function.identity(), Function.identity()));

        System.out.println(map);

    }

}

Output:

{apple=apple, banana=banana, cherry=cherry}

Is t -> t same as Function.identity() method in Java?

import java.util.function.Function;

public class IdentityFunctionCompare {

    public static void main(String args[]) 

    {

        Function<Integer, Integer> funcIdentity = Function.identity();

        Function<Integer, Integer> funcIdentity1 = Function.identity();

        Function<Integer, Integer> funcIdentity2 = Function.identity();

        

        Function<Integer, Integer> intFuncMap1 = t -> t;

        Function<Integer, Integer> intFuncMap = t -> t;

        Function<Integer, Integer> intFuncMap = t -> t;

        

        System.out.println(funcIdentity);

        System.out.println(funcIdentity1);

        System.out.println(funcIdentity2);

        

        System.out.println(intFuncMap1);

        System.out.println(intFuncMap2);

        System.out.println(intFuncMap3);

    }

}

Output:

java.util.function.Function$$Lambda$1/0x0000000800034d78@b1d7fff

java.util.function.Function$$Lambda$1/0x0000000800034d78@b1d7fff

java.util.function.Function$$Lambda$1/0x0000000800034d78@b1d7fff

IdentityFunctionExample3$$Lambda$2/0x0000000800000a08@3e5c649

IdentityFunctionExample3$$Lambda$3/0x0000000800000c48@136432db

IdentityFunctionExample3$$Lambda$4/0x0000000800001000@6382f612