Java Lambda - Function identity example

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Function identity returns a function that always returns its input argument.

Syntax

identity has the following syntax.

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

Example

The following example shows how to use identity.

import java.util.function.Function;
/*w w  w  . ja  v a 2  s. co m*/
public class Main {

  public static void main(String[] args) {
    Function<Integer,Integer> id = Function.identity();
    
    System.out.println(id.apply(3));

  }
}

The code above generates the following result.

Example 2

The following code shows how to use Function.identity() to not modify values.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
/*  w ww.  ja  va 2 s .c o  m*/
public class Main {
   public static void main(String[] args) {
      Function<Double, Double> square = number -> number * number;
      Function<Double, Double> half = number -> number * 2;

      List<Double> numbers = Arrays.asList(10D, 4D, 12D);
      // you can use identity to not modify them
      System.out.println(mapIt(numbers, Function.<Double>identity()));
   }

   private static List<Double> mapIt(List<Double> numbers, Function<Double, Double> fx) {
      List<Double> result = new ArrayList<>();

      for (Double number : numbers) {
         result.add(fx.apply(number));
      }

      return result;
   }
}

The code above generates the following result.

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