How to Fill (initialize at once) an Array in Java

All the elements of an array can be initialized at once using methods from the Arrays utility class in Java. One common method used is Arrays.fill(), which can initialize the entire array or a specific portion of it with a single value.

Filling an Array

The Arrays.fill() method is used to initialize all the elements of an array to a specific value. The first use of Arrays.fill() fills the entire array with the value 100. Then, the second use of Arrays.fill() is applied to a specific range of the array (from index 3 to index 6) with the value 50.

Syntax

The following is the syntax for java.util.Arrays.fill() method

public static void fill(object[] a, int fromIndex, int toIndex, object val)

Example 1

This example fill (initialize all the elements of the array in one short) an array by using Array.fill(arrayname,value) method and Array.fill(arrayname, starting index, ending index, value) method of Java Util class

import java.util.*;

public class FillTest {
   public static void main(String args[]) {
      int array[] = new int[6];
      Arrays.fill(array, 100);
      
      for (int i = 0, n = array.length; i < n; i++) {
         System.out.println(array[i]);
      }
      System.out.println();
      Arrays.fill(array, 3, 6, 50);
      
      for (int i = 0, n = array.length; i < n; i++) {
         System.out.println(array[i]);
      }
   }
}

Output

100
100
100
100
100
100

100
100
100
50
50
50

Example 2

An integer array is initialized with specific values: 1, 6, 3, 2, 9. After printing the original values, the Arrays.fill() method is used to change all the elements of the array to the value 18. The following is an example of array filling

import java.util.Arrays;

public class HelloWorld {
   public static void main(String[] args) {
      // initializing int array
      int arr[] = new int[] {1, 6, 3, 2, 9};
      
      // let us print the values
      System.out.println("Actual values: ");
      
      for (int value : arr) {
         System.out.println("Value = " + value);
      } 
      
      // using fill for placing 18
      Arrays.fill(arr, 18);
      
      // let us print the values
      System.out.println("New values after using fill() method: ");
      
      for (int value : arr) {
         System.out.println("Value = " + value);
      }
   }
}

Output

Actual values: 
Value = 1
Value = 6
Value = 3
Value = 2
Value = 9
New values after using fill() method: 
Value = 18
Value = 18
Value = 18
Value = 18
Value = 18    .