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Implements the Set interface, backed by a ConcurrentHashMap instance
/*
* 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);
}
}
}
