Checks if a concurrent map contains a key and creates a corresponding value if not, suppressing checked exceptions. - Java java.util.concurrent

Java examples for java.util.concurrent:ConcurrentMap

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Description

Checks if a concurrent map contains a key and creates a corresponding value if not, suppressing checked exceptions.

Demo Code

/*//from   w ww  .j  a va  2s  .c  om
 * 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
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 */
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class Main{
    /**
     * Checks if a concurrent map contains a key and creates a corresponding
     * value if not, suppressing checked exceptions. This method calls
     * {@code createIfAbsent()}. If a {@link ConcurrentException} is thrown, it
     * is caught and re-thrown as a {@link ConcurrentRuntimeException}.
     *
     * @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 init the {@link ConcurrentInitializer} for creating the value
     * @return the value stored in the map after this operation; this may or may
     * not be the object created by the {@link ConcurrentInitializer}
     * @throws ConcurrentRuntimeException if the initializer throws an exception
     */
    public static <K, V> V createIfAbsentUnchecked(ConcurrentMap<K, V> map,
            K key, ConcurrentInitializer<V> init) {
        try {
            return createIfAbsent(map, key, init);
        } catch (ConcurrentException cex) {
            throw new ConcurrentRuntimeException(cex.getCause());
        }
    }
    /**
     * Checks if a concurrent map contains a key and creates a corresponding
     * value if not. This method first checks the presence of the key in the
     * given map. If it is already contained, its value is returned. Otherwise
     * the {@code get()} method of the passed in {@link ConcurrentInitializer}
     * is called. With the resulting object
     * {@link #putIfAbsent(ConcurrentMap, Object, Object)} is called. This
     * handles the case that in the meantime another thread has added the key to
     * the map. Both the map and the initializer can be <b>null</b>; in this
     * case this method simply returns <b>null</b>.
     *
     * @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 init the {@link ConcurrentInitializer} for creating the value
     * @return the value stored in the map after this operation; this may or may
     * not be the object created by the {@link ConcurrentInitializer}
     * @throws ConcurrentException if the initializer throws an exception
     */
    public static <K, V> V createIfAbsent(ConcurrentMap<K, V> map, K key,
            ConcurrentInitializer<V> init) throws ConcurrentException {
        if (map == null || init == null) {
            return null;
        }

        V value = map.get(key);
        if (value == null) {
            return putIfAbsent(map, key, init.get());
        }
        return value;
    }
    /**
     * <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;
    }
}

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