7.10 The ArrayList class

In addition to arrays, Java provides the class ArrayList to implement a list. Unlike an array, the size of a ArrayList object can grow and shrink during program execution. Therefore, you need not be concerned about the number of data elements. The elements of a ArrayList are references to Object. Using a ArrayList is slightly slower than using an array.

/**
 * This program demonstrates an ArrayList
 * and its methods
 */
import java.util.ArrayList;    // Needed for ArrayList class

public class ArrayListDemo
{
   public static void main(String[] args)
   {
      // Create an array list.
      ArrayList<String> list = new ArrayList<>();

      // Display the size of the array list.
      System.out.println("Initial size of list: " + list.size());

      // Add elements to the array list.
      list.add("Sunday");
      list.add("Tuesday");
      list.add("Wednesday");
      list.add("Thursday");
      list.add("Friday");
      list.add("Saturday");

      // Now insert an  item at index 1.
      list.add(1, "Monday");

      // Display the size of the array list.
      System.out.println("Size of list after additions: "
                         + list.size());

      // Display the array list.
      System.out.println("Contents of list: " + list);

      // Remove elements from the array list.
      list.remove("Saturday");

      // Display the array list.
      System.out.println("Contents of list: " + list);

      // Now remove the item at index 2.
      list.remove(2);

      // Display the array list.
      System.out.println("Contents of list: " + list);
   }
}

ArrayList Objects and the foreach Loop

A foreach loop can be used to process the elements of a ArrayList object one at a time. For example, suppose list is an object of ArrayList class of String objects, The code for foreach loop will look like this :

for (String str : list)
{
    //write code here
}

Example

import java.util.ArrayList;    // Needed for ArrayList class

/**
 *  This program demonstrates foreach loop.
 */
public class ForEachDemo
{
   public static void main(String[] args)
   {
      // Create an ArrayList.
      ArrayList<String> list = new ArrayList<>();

      // Add some values to the ArrayList.
      list.add("One");
      list.add("Two");
      list.add("Three");

      for (String str : list)
      {
         System.out.println(str);
      }
   }
}