ArrayLists and Iterators

13. Adding at a Specific Index

Answer:
element 0: Amy
element 1: Bob
element 2: Cindy

element 0: Zoe
element 1: Bob
element 2: Cindy

Adding at a Specific Index

You can insert an element at a specific index from 0 to size(). The newly added element is now located at the specified index, and the indexes of all elements above that element is increased by one. If you add an element at index size(), the element is appended to the end of the list.

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

The method throws an IndexOutOfBoundsException if the index is out of bounds, either negative or greater than size(). This prevents you from creating a list with gaps between elements. The following program uses this method:

              
import java.util.* ;

public 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

Question 13:
Would the following statement work in the above program?
names.add(5, "Gertrude");