org.apache.hadoop.util.GSet.java Source code

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Here is the source code for org.apache.hadoop.util.GSet.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.
 */
package org.apache.hadoop.util;

import java.util.Collection;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;

/**
 * A {@link GSet} is set,
 * which supports the {@link #get(Object)} operation.
 * The {@link #get(Object)} operation uses a key to lookup an element.
 * 
 * Null element is not supported.
 * 
 * @param <K> The type of the keys.
 * @param <E> The type of the elements, which must be a subclass of the keys.
 */
@InterfaceAudience.Private
public interface GSet<K, E extends K> extends Iterable<E> {
    static final Log LOG = LogFactory.getLog(GSet.class);

    /**
     * @return The size of this set.
     */
    int size();

    /**
     * Does this set contain an element corresponding to the given key?
     * @param key The given key.
     * @return true if the given key equals to a stored element.
     *         Otherwise, return false.
     * @throws NullPointerException if key == null.
     */
    boolean contains(K key);

    /**
     * Return the stored element which is equal to the given key.
     * This operation is similar to {@link java.util.Map#get(Object)}.
     * @param key The given key.
     * @return The stored element if it exists.
     *         Otherwise, return null.
     * @throws NullPointerException if key == null.
     */
    E get(K key);

    /**
     * Add/replace an element.
     * If the element does not exist, add it to the set.
     * Otherwise, replace the existing element.
     *
     * Note that this operation
     * is similar to {@link java.util.Map#put(Object, Object)}
     * but is different from {@link java.util.Set#add(Object)}
     * which does not replace the existing element if there is any.
     *
     * @param element The element being put.
     * @return the previous stored element if there is any.
     *         Otherwise, return null.
     * @throws NullPointerException if element == null.
     */
    E put(E element);

    /**
     * Remove the element corresponding to the given key. 
     * This operation is similar to {@link java.util.Map#remove(Object)}.
     * @param key The key of the element being removed.
     * @return If such element exists, return it.
     *         Otherwise, return null. 
      * @throws NullPointerException if key == null.
    */
    E remove(K key);

    /**
     * Clear the set.
     */
    void clear();

    /**
     * Returns a {@link Collection} view of the values contained in this set.
     * The collection is backed by the set, so changes to the set are
     * reflected in the collection, and vice-versa.
     *
     * @return the collection of values.
     */
    Collection<E> values();
}