ConcurrentHashSet.java Source code

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Here is the source code for ConcurrentHashSet.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.ObjectInputStream;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

/**
 * This class implements the <tt>Set</tt> interface, backed by a ConcurrentHashMap instance.
 * 
 * @author Matt Tucker
 * @param <E>
 */
public class ConcurrentHashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable {
    /** */
    private static final long serialVersionUID = 1L;

    private transient ConcurrentHashMap<E, Object> map;

    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();

    /**
     * Constructs a new, empty set; the backing <tt>ConcurrentHashMap</tt> instance has default
     * initial capacity (16) and load factor (0.75).
     */
    public ConcurrentHashSet() {
        map = new ConcurrentHashMap<E, Object>();
    }

    /**
     * Constructs a new set containing the elements in the specified collection. The
     * <tt>ConcurrentHashMap</tt> is created with default load factor (0.75) and an initial capacity
     * sufficient to contain the elements in the specified collection.
     * 
     * @param c
     *            the collection whose elements are to be placed into this set.
     * @throws NullPointerException
     *             if the specified collection is null.
     */
    public ConcurrentHashSet(Collection<? extends E> c) {
        map = new ConcurrentHashMap<E, Object>(Math.max((int) (c.size() / .75f) + 1, 16));
        addAll(c);
    }

    /**
     * Constructs a new, empty set; the backing <tt>ConcurrentHashMap</tt> instance has the
     * specified initial capacity and the specified load factor.
     * 
     * @param initialCapacity
     *            the initial capacity of the hash map.
     * @param loadFactor
     *            the load factor of the hash map.
     * @throws IllegalArgumentException
     *             if the initial capacity is less than zero, or if the load factor is nonpositive.
     */
    public ConcurrentHashSet(int initialCapacity, float loadFactor) {
        map = new ConcurrentHashMap<E, Object>(initialCapacity, loadFactor, 16);
    }

    /**
     * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has the specified initial
     * capacity and default load factor, which is <tt>0.75</tt>.
     * 
     * @param initialCapacity
     *            the initial capacity of the hash table.
     * @throws IllegalArgumentException
     *             if the initial capacity is less than zero.
     */
    public ConcurrentHashSet(int initialCapacity) {
        map = new ConcurrentHashMap<E, Object>(initialCapacity);
    }

    /**
     * 
     * @see java.util.AbstractCollection#iterator()
     */
    @Override
    public Iterator<E> iterator() {
        return map.keySet().iterator();
    }

    /**
     * 
     * @see java.util.AbstractCollection#size()
     */
    @Override
    public int size() {
        return map.size();
    }

    /**
     * 
     * @see java.util.AbstractCollection#isEmpty()
     */
    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    /**
     * 
     * @see java.util.AbstractCollection#contains(java.lang.Object)
     */
    @Override
    public boolean contains(Object o) {
        return map.containsKey(o);
    }

    /**
     * 
     * @see java.util.AbstractCollection#add(java.lang.Object)
     */
    @Override
    public boolean add(E o) {
        return map.put(o, PRESENT) == null;
    }

    /**
     * 
     * @see java.util.AbstractCollection#remove(java.lang.Object)
     */
    @Override
    public boolean remove(Object o) {
        return map.remove(o) == PRESENT;
    }

    /**
     * 
     * @see java.util.AbstractCollection#clear()
     */
    @Override
    public void clear() {
        map.clear();
    }

    /**
     * 
     * @see java.lang.Object#clone()
     */
    @SuppressWarnings("unchecked")
    @Override
    public Object clone() {
        try {
            ConcurrentHashSet<E> newSet = (ConcurrentHashSet<E>) super.clone();
            newSet.map.putAll(map);
            return newSet;
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
    }

    /**
     * 
     * @param s
     * @throws java.io.IOException
     */
    private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
        s.defaultWriteObject();
        s.writeInt(map.size());

        for (Iterator<E> i = map.keySet().iterator(); i.hasNext();) {
            s.writeObject(i.next());
        }
    }

    /**
     * Re-constitute the <tt>HashSet</tt> instance from a stream.
     * 
     * @param inputStream
     * @throws ClassNotFoundException
     * @throws IOException
     */
    private void readObject(ObjectInputStream inputStream) throws ClassNotFoundException, IOException {
        inputStream.defaultReadObject();

        map = new ConcurrentHashMap<E, Object>();

        int size = inputStream.readInt();
        for (int i = 0; i < size; i++) {
            E e = (E) inputStream.readObject();
            map.put(e, PRESENT);
        }
    }
}