com.phoenixst.collections.AbstractSingletonCollection.java Source code

Introduction

Here is the source code for com.phoenixst.collections.AbstractSingletonCollection.java

Source

/*
 *  $Id: AbstractSingletonCollection.java,v 1.11 2006/06/07 19:28:12 rconner Exp $
 *
 *  Copyright (C) 1994-2006 by Phoenix Software Technologists,
 *  Inc. and others.  All rights reserved.
 *
 *  THIS PROGRAM AND DOCUMENTATION IS PROVIDED UNDER THE TERMS OF THE
 *  COMMON PUBLIC LICENSE ("AGREEMENT") WHICH ACCOMPANIES IT.  ANY
 *  USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM CONSTITUTES
 *  RECIPIENT'S ACCEPTANCE OF THE AGREEMENT.
 *
 *  The license text can also be found at
 *    http://opensource.org/licenses/cpl.php
 */

package com.phoenixst.collections;

import java.util.*;

import org.apache.commons.collections.iterators.EmptyIterator;

/**
 *  A modifiable, lazy singleton <code>Collection</code> view.  This
 *  view may be empty at any given point in time.
 *
 *  @version    $Revision: 1.11 $
 *  @author     Ray A. Conner
 *
 *  @since      1.0
 */
public abstract class AbstractSingletonCollection implements Collection {

    private final Object element;

    /**
     *  Creates a new <code>AbstractSingletonCollection</code>.
     */
    protected AbstractSingletonCollection(Object element) {
        super();
        this.element = element;
    }

    protected final Object getElement() {
        return element;
    }

    protected abstract boolean removeElement();

    public abstract boolean isEmpty();

    public int size() {
        return isEmpty() ? 0 : 1;
    }

    /**
     *  Throws an <code>UnsupportedOperationException</code>.
     */
    public boolean add(Object object) {
        throw new UnsupportedOperationException();
    }

    public boolean remove(Object object) {
        return (element == object || (element != null && element.equals(object))) && removeElement();
    }

    public boolean contains(Object object) {
        return (element == object || (element != null && element.equals(object))) && !isEmpty();
    }

    public Iterator iterator() {
        return isEmpty() ? EmptyIterator.INSTANCE : new IteratorImpl(this);
    }

    public boolean containsAll(Collection collection) {
        if (isEmpty()) {
            return collection.isEmpty();
        }
        if (element == null) {
            for (Iterator i = collection.iterator(); i.hasNext();) {
                if (i.next() != null) {
                    return false;
                }
            }
        } else {
            for (Iterator i = collection.iterator(); i.hasNext();) {
                if (!element.equals(i.next())) {
                    return false;
                }
            }
        }
        return true;
    }

    /**
     *  Throws an <code>UnsupportedOperationException</code>.
     */
    public boolean addAll(Collection collection) {
        throw new UnsupportedOperationException();
    }

    public boolean removeAll(Collection collection) {
        return collection.contains(element) && removeElement();
    }

    public boolean retainAll(Collection collection) {
        return !collection.contains(element) && removeElement();
    }

    public void clear() {
        removeElement();
    }

    public Object[] toArray() {
        return isEmpty() ? new Object[0] : new Object[] { element };
    }

    public Object[] toArray(Object[] array) {
        int size = size();
        if (size > 0) {
            if (array.length == 0) {
                array = (Object[]) java.lang.reflect.Array.newInstance(array.getClass().getComponentType(), 1);
            }
            array[0] = element;
        }
        if (array.length > size) {
            array[size] = null;
        }
        return array;
    }

    public String toString() {
        if (isEmpty()) {
            return "[]";
        }
        StringBuilder s = new StringBuilder();
        s.append("[");
        s.append(element);
        s.append("]");
        return s.toString();
    }

    private static class IteratorImpl implements Iterator {
        private final AbstractSingletonCollection collection;
        private boolean hasNext = true;
        private boolean elementRemoved = false;

        IteratorImpl(AbstractSingletonCollection collection) {
            super();
            this.collection = collection;
        }

        public boolean hasNext() {
            return hasNext;
        }

        public Object next() {
            if (!hasNext) {
                throw new NoSuchElementException();
            }
            hasNext = false;
            return collection.getElement();
        }

        public void remove() {
            if (hasNext || elementRemoved) {
                throw new IllegalStateException();
            }
            collection.removeElement();
            elementRemoved = true;
        }
    }

}