How to create a constructor reference for an array in Java?

In this article, we will learn to create a constructor reference for an array in Java. In Java, constructor references provide a concise way to refer to constructors using lambda expressions. While they are commonly used for object initialization, they can also be used for array declaration.

What is a Constructor Reference?

A constructor reference is similar to method reference except that the name of a method is new. We can also create a constructor reference with an array type. For instance, if we need to create an integer array by using the constructor reference: int[]:: new, where the parameter is a length of an array.

Syntax

ArrayTypeName[]::new

Following are the steps to implementing an array constructor reference ?

• Functional Interface: The ArrayCreator defines makeArray(int number) for an array declaration.
  
• Constructor Reference: The int[]:: new expression dynamically creates an array of the mentioned size.
  
• Output: The elements are added to the array using a for-loop and printed.

ArrayCreator arrayCreator = int[]::new;

Example

Below is an example of implementing an array constructor reference ?

@FunctionalInterface
interface ArrayCreator {
   int[] makeArray(int number);
}
public class ArrayConstructorRefTest {
   public static void main(String[] args) {
      ArrayCreator arrayCreator = int[]::new;   // Constructor Reference for an Array
      int[] intArray = arrayCreator.makeArray(10);
      for(int i = 0; i < intArray.length; i++) {
         intArray[i] = i * i - i / 2;
         System.out.println("[" + i + "] = " + intArray[i]);
      }
   }
}

Output

[0] = 0
[1] = 1
[2] = 3
[3] = 8
[4] = 14
[5] = 23
[6] = 33
[7] = 46
[8] = 60
[9] = 77

Time complexity: O(n), for initializing the array and filling the elements.
Space complexity: O(n), for storing the array of size n.

Conclusion

In this article, we discovered how to use constructor references to initialize arrays in Java. Rather than coding additional, we can use `int[]::new` and create an array of any size. This reduces the code length and makes it more readable.