org.apache.dubbo.common.utils.ConcurrentHashSet Maven / Gradle / Ivy

/*
 * 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.
 */
package org.apache.dubbo.common.utils;

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

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 ConcurrentMap 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
     */
    @Override
    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)
     */
    @Override
    public int size() {
        return map.size();
    }

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

}