Adding at a Specific Index

You can insert an element at a specific index from 0 ... size()-1. The newly added element is now located at the specified index, and all elements above that element have their index increased by one.

void add(int index, E elt)  //  Inserts the element at index. Each element with 
                            //  an index greater than index is shifted upward 
                            //  to have an index one greater than its previous value. 

The method throws an IndexOutOfBoundsException if the index is out of bounds. No "gaps" in the list can be created by using this method. The following program uses this method:

import java.util.* ;

class ArrayListEgFour
{

  public static void main ( String[] args)
  {
    ArrayList<String> names = new ArrayList<String>();

    names.add( "Amy" );
    names.add( "Bob" );
    names.add( "Chris" );

    // Print original arrangement
    System.out.println("Before adding at index 1:");
    for ( int j=0; j < names.size(); j++ )
      System.out.println( j + ": " + names.get(j) ); 
      
    // Insert an element
    names.add( 1, "Valerie");

    // Print new arrangement
    System.out.println("\nAfter adding at index 1:");
    for ( int j=0; j < names.size(); j++ )
      System.out.println( j + ": " + names.get(j) ); 

  }
}

The program prints out:

Before adding at index 1:
0: Amy
1: Bob
2: Chris

After adding at index 1:
0: Amy
1: Valerie
2: Bob
3: Chris