/*

* Copyright 2009 Weaver authors

*

* This code is part of the Weaver tutorial and may be freely used.

*/

import java.util.ArrayList;

/**

* Implementation of {@link java.util.ArrayList} that allows

* an element to be added only if it is not already in the list.

* <p>

* This class is designed to demonstrate the testing of race conditions,

* and is not intended to be complete or correct.

*

* @param <E> the list element

*

* @author alasdair.mackintosh@gmail.com (Alasdair Mackintosh)

*/

public class UniqueList<E> extends ArrayList<E> {

/**

* Adds an element iff it is not already present in this list. Returns true

* if the element was added, and false if it was already found.

*/

public boolean putIfAbsent(E elem) {

return putIfAbsentInternal(elem);

}

// The actual method that we want to test is a private one. To make this work, we

// specify the name of this method in the test setup. See

// UniqueListTest.testPutIfAbsent()

private boolean putIfAbsentInternal(E elem) {

boolean absent = !super.contains(elem);

if (absent) {

super.add(elem);

}

return absent;

}

}