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Java - How to insert new element in an array by index?

[Updated: Aug 25, 2018, Created: Aug 25, 2018]

Java Arrays 

Following example shows how to insert a new element to an array:

package com.logicbig.example;

import java.lang.reflect.Array;
import java.util.Arrays;

public class ArrayInsert {

  //insert array of objects
  public static <T> T[] insert(T[] input, T newT, int index) {
      if (input == null) {
          return input;
      }
      T[] newArray = (T[]) Array.newInstance(input.getClass().getComponentType(), input.length + 1);
      int c = 0;
      for (int i = 0; i < input.length + 1; i++) {
          newArray[i] = i == index ? newT : input[c++];
      }
      return newArray;
  }

  //insert array of primitive int
  public static int[] insert(int[] input, int newT, int index) {
      if (input == null) {
          return input;
      }
      int[] newArray = new int[input.length + 1];
      int c = 0;
      for (int i = 0; i < input.length + 1; i++) {
          newArray[i] = i == index ? newT : input[c++];
      }
      return newArray;
  }

  public static void main(String[] args) {
      int[] intArray = {3, 6, 4, 8};
      intArray = insert(intArray, 9, 3);
      System.out.println(Arrays.toString(intArray));

      String[] strArray = {"one", "two", "three"};
      strArray = insert(strArray, "two-two", 2);
      System.out.println(Arrays.toString(strArray));
  }
}
[3, 6, 4, 9, 8]
[one, two, two-two, three]

The object version of insert method, in above example, is generic for all objects but for primitives we have to create separate methods individually for each primitive. In above example we showed how to do that with int array.

See Also