com.alibaba.dubbo.common.utils.ConcurrentHashSet Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of dubbo2 Show documentation
The all in one project of dubbo2
The newest version!
/*
 * Copyright 1999-2011 Alibaba Group.
 *  
 * Licensed 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.
 */
package com.alibaba.dubbo.common.utils;

import java.util.AbstractSet;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashSet extends AbstractSet implements Set, java.io.Serializable {

	private static final long serialVersionUID = -8672117787651310382L;

	private static final Object PRESENT = new Object();

	private final ConcurrentHashMap map;
	
	public ConcurrentHashSet(){
	    map = new ConcurrentHashMap();
	}

    public ConcurrentHashSet(int initialCapacity){
        map = new ConcurrentHashMap(initialCapacity);
    }

	/**
	 * Returns an iterator over the elements in this set. The elements are
	 * returned in no particular order.
	 * 
	 * @return an Iterator over the elements in this set
	 * @see ConcurrentModificationException
	 */
	public Iterator iterator() {
		return map.keySet().iterator();
	}

	/**
	 * Returns the number of elements in this set (its cardinality).
	 * 
	 * @return the number of elements in this set (its cardinality)
	 */
	public int size() {
		return map.size();
	}

	/**
	 * Returns true if this set contains no elements.
	 * 
	 * @return true if this set contains no elements
	 */
	public boolean isEmpty() {
		return map.isEmpty();
	}

	/**
	 * Returns true if this set contains the specified element. More
	 * formally, returns true if and only if this set contains an
	 * element e such that
	 * (o==null ? e==null : o.equals(e)).
	 * 
	 * @param o
	 *            element whose presence in this set is to be tested
	 * @return true if this set contains the specified element
	 */
	public boolean contains(Object o) {
		return map.containsKey(o);
	}

	/**
	 * Adds the specified element to this set if it is not already present. More
	 * formally, adds the specified element e to this set if this set
	 * contains no element e2 such that
	 * (e==null ? e2==null : e.equals(e2)). If this
	 * set already contains the element, the call leaves the set unchanged and
	 * returns false.
	 * 
	 * @param e
	 *            element to be added to this set
	 * @return true if this set did not already contain the specified
	 *         element
	 */
	public boolean add(E e) {
		return map.put(e, PRESENT) == null;
	}

	/**
	 * Removes the specified element from this set if it is present. More
	 * formally, removes an element e such that
	 * (o==null ? e==null : o.equals(e)), if this
	 * set contains such an element. Returns true if this set contained
	 * the element (or equivalently, if this set changed as a result of the
	 * call). (This set will not contain the element once the call returns.)
	 * 
	 * @param o
	 *            object to be removed from this set, if present
	 * @return true if the set contained the specified element
	 */
	public boolean remove(Object o) {
		return map.remove(o) == PRESENT;
	}

	/**
	 * Removes all of the elements from this set. The set will be empty after
	 * this call returns.
	 */
	public void clear() {
		map.clear();
	}

}