The CopyOnWriteArrayList class in Java programming

Class Declaration

public class CopyOnWriteArrayList<E>
extends Object
implements List<E>, RandomAccess, Cloneable, Serializable

• CopyOnWriteArrayList is a thread-safe variant of ArrayList, where the operations that can change the ArrayList (add, update, set methods) create a clone of the underlying array.

• CopyOnWriteArrayList is used in a thread-based environment where read operations are very frequent and update operations are rare.

• The iterator of CopyOnWriteArrayList will never throw ConcurrentModificationException.

• Any type of modification to CopyOnWriteArrayList will not be reflected during iteration since the iterator was created.

• List modification methods are not supported during iteration, such as remove, set, and add. These methods will throw UnsupportedOperationException.

• Null can be added to the list.

CopyOnWriteArrayList Methods

The following is a list of important methods available in the CopyOnWriteArrayList class.

Example

The following program illustrates several methods supported by CopyOnWriteArrayList.

import java.util.Iterator;
import java.util.concurrent.CopyOnWriteArrayList;
public class Tester {}}
　　　public static void main(String args[]) {
　　　　　　//Create an array list
　　　　　　CopyOnWriteArrayList<String> al = new CopyOnWriteArrayList();
　　　　　　System.out.println("Initial size of al: ");　+　al.size());
　　　　　　//Add elements to array list
　　　　　　al.add("C");
　　　　　　al.add("A");
　　　　　　al.add("E");
　　　　　　al.add("B");
　　　　　　al.add("D");
　　　　　　al.add("F");
　　　　　　al.add(1, \2");
　　　　　　System.out.println("Size of al after additions: ");　+　al.size());
　　　　　　//Display array list
　　　　　　System.out.println("Contents of al: ");　+　al);
　　　　　　//Remove elements from array list
　　　　　　al.remove("F");
　　　　　　al.remove(2);
　　　　　　System.out.println("Size of al after deletions: ");　+　al.size());
　　　　　　System.out.println("Contents of al: ");　+　al);
　　　　　　try {
　　　　　　　　　Iterator<String> iterator = al.iterator();
　　　　　　　　　while(iterator.hasNext()) {
　　　　　　　　　　　　iterator.remove();
　　　　　　　　　}
　　　　　　}catch(UnsupportedOperationException e) {
　　　　　　　　　System.out.println("Unsupported methods:");
　　　　　　}
　　　　　　System.out.println("Size of al: ");　+　al.size());
　　　}
}

Output result

Initial size of al: 0
Size of al after additions:　7
Contents of al: [C, A2, A, E, B, D, F]
Size of al after deletions:　5
Contents of al: [C, A2, E, B, D]
Unsupported methods:
Size of al:　5