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An ordered collection is called a List.  A concrete implementation of a List is ArrayList:

Object
    AbstractCollection (implements Collection)
        AbstractList (implements List)
            AbstractSequentialList
                LinkedList
            ArrayList
            Vector
                Stack
        AbstractSet (implements Set)
            HashSet
            TreeSet (implements SortedSet)
    AbstractMap (implements Map)
        HashMap
        TreeMap (implements SortedMap)
        WeakHashMap
    Dictionary
        Hashtable (implements Map)
            Properties

ArrayList implements the List as a resizeable array, but that is just one possible implementation of a List.  There are others.

Here's an example of how one could use an instance of class ArrayList.  It will run only under JDK 1.2 and beyond:

package examples;

import java.util.ArrayList;
import java.util.Iterator;

public class ArrayListExample
{
  public static void main(String[] args)
  {
    ArrayList list = new ArrayList();
    list.add("Mary");
    list.add("Frank");
    list.add("Joe");
    list.add("Sylvia");
    list.add("Vanessa");

    for (int i = 0; i < list.size(); i++)
    {
      String name = (String) list.get(i); // Note required cast
      System.out.println(i + ": " + name);
    }

    for (Iterator iter = list.iterator(); iter.hasNext(); )
    {
      String name = (String) iter.next(); // Note required cast
      System.out.println(name);
    }
  }
}

which produces the output:

0: Mary
1: Frank
2: Joe
3: Sylvia
4: Vanessa
Mary
Frank
Joe
Sylvia
Vanessa

The output is exactly the same as for the earlier Vector/Enumeration example.

Again, note the two ways of obtaining the elements of the list:

• Access each element by its index, using the get(int index) method
• Access each element through an Iterator object, supplied by the ArrayList. (Remember, Iterator is an interface.)

This is the "new style".

This page was last modified on 02 October, 2007