Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
/*
 * 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.util.concurrent.ConcurrentMap;

public class Main {
    /**
     * <p>
     * Puts a value in the specified {@code ConcurrentMap} if the key is not yet
     * present. This method works similar to the {@code putIfAbsent()} method of
     * the {@code ConcurrentMap} interface, but the value returned is different.
     * Basically, this method is equivalent to the following code fragment:
     *
     * <pre>
     * if (!map.containsKey(key)) {
     *     map.put(key, value);
     *     return value;
     * } else {
     *     return map.get(key);
     * }
     * </pre>
     *
     * except that the action is performed atomically. So this method always
     * returns the value which is stored in the map.
     * </p>
     * <p>
     * This method is <b>null</b>-safe: It accepts a <b>null</b> map as input
     * without throwing an exception. In this case the return value is
     * <b>null</b>, too.
     * </p>
     *
     * @param <K> the type of the keys of the map
     * @param <V> the type of the values of the map
     * @param map the map to be modified
     * @param key the key of the value to be added
     * @param value the value to be added
     * @return the value stored in the map after this operation
     */
    public static <K, V> V putIfAbsent(ConcurrentMap<K, V> map, K key, V value) {
        if (map == null) {
            return null;
        }

        V result = map.putIfAbsent(key, value);
        return result != null ? result : value;
    }
}