Java Lambda - Java Constructor Reference

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We can use constructor to create a lambda expression.

The syntax to use a constructor reference is

The keyword new refers to the constructor of the class. The compiler chooses a constructor based on the context.

import java.util.function.Function;
import java.util.function.Supplier;
//from w  w  w  . java  2  s.  com
public class Main{
  public static void main(String[] argv){
    Supplier<String> func1  = () ->  new String();
    System.out.println("Empty String:"+func1.get());
    
    Function<String,String> func2  = str ->  new String(str);
    
    System.out.println(func2.apply("java2s.com"));

    Supplier<String> func3  = String::new;
    System.out.println("Empty String:"+func3.get());
    
    Function<String,String> func4  = String::new;
    System.out.println(func4.apply("java2s.com"));
  }
}

The code above generates the following result.

Array Constructor References

We can create an array using array constructor as follows.

int[]::new is calling new int[]. new int[] requires an int type value as the array length, therefore the int[]::new needs an int type input value.

The following code uses the array constructor reference to create an int array.

import java.util.Arrays;
import java.util.function.IntFunction;
/*from  ww  w  . j a v a  2 s .  c om*/
public class Main{
  public static void main(String[] argv){
    IntFunction<int[]> arrayCreator1 = size ->  new int[size];
    // Creates an  int array of  five  elements
    int[] intArray1  = arrayCreator1.apply(5);
    System.out.println(Arrays.toString(intArray1));

    IntFunction<int[]> arrayCreator2 = int[]::new;
    int[] intArray2 = arrayCreator2.apply(5); 
    System.out.println(Arrays.toString(intArray2));
  }
}

The code above generates the following result.

Example 2

By using Function<Integer,ArrayType> we can specify array type in the declaration.

import java.util.Arrays;
import java.util.function.Function;
/*from w  w  w . j a v a  2 s .co  m*/
public class Main{
  public static void main(String[] argv){
    Function<Integer,int[]>  arrayCreator3 = int[]::new;
    int[] intArray  = arrayCreator3.apply(5); 
    System.out.println(Arrays.toString(intArray));
  }
}

The code above generates the following result.

Example 3

We can specify the length for the first dimension when creating a two-dimensional array.

import java.util.Arrays;
import java.util.function.IntFunction;
//from   w ww  .  j  a v  a 2s  .c  o m
public class Main{
  public static void main(String[] argv){
    IntFunction<int[][]> TwoDimArrayCreator  = int[][]::new;
    int[][] intArray = TwoDimArrayCreator.apply(5); 
    // Creates an  int[5][]  array
    intArray[0] = new int[5]; 
    intArray[1] = new int[5];
    intArray[2] = new int[5];
    intArray[3] = new int[5];
    intArray[4] = new int[5];
    
    System.out.println(Arrays.deepToString(intArray));
  }
}

The code above generates the following result.

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