    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017    package org.apache.commons.lang3.concurrent;
    018
    019    import org.apache.commons.lang3.ObjectUtils;
    020
    021    /**
    022     * <p>
    023     * A very simple implementation of the {@link ConcurrentInitializer} interface
    024     * which always returns the same object.
    025     * </p>
    026     * <p>
    027     * An instance of this class is passed a reference to an object when it is
    028     * constructed. The {@link #get()} method just returns this object. No
    029     * synchronization is required.
    030     * </p>
    031     * <p>
    032     * This class is useful for instance for unit testing or in cases where a
    033     * specific object has to be passed to an object which expects a
    034     * {@link ConcurrentInitializer}.
    035     * </p>
    036     *
    037     * @since 3.0
    038     * @version $Id: ConstantInitializer.java 1199894 2011-11-09 17:53:59Z ggregory $
    039     * @param <T> the type of the object managed by this initializer
    040     */
    041    public class ConstantInitializer<T> implements ConcurrentInitializer<T> {
    042        /** Constant for the format of the string representation. */
    043        private static final String FMT_TO_STRING = "ConstantInitializer@%d [ object = %s ]";
    044
    045        /** Stores the managed object. */
    046        private final T object;
    047
    048        /**
    049         * Creates a new instance of {@code ConstantInitializer} and initializes it
    050         * with the object to be managed. The {@code get()} method will always
    051         * return the object passed here. This class does not place any restrictions
    052         * on the object. It may be <b>null</b>, then {@code get()} will return
    053         * <b>null</b>, too.
    054         *
    055         * @param obj the object to be managed by this initializer
    056         */
    057        public ConstantInitializer(T obj) {
    058            object = obj;
    059        }
    060
    061        /**
    062         * Directly returns the object that was passed to the constructor. This is
    063         * the same object as returned by {@code get()}. However, this method does
    064         * not declare that it throws an exception.
    065         *
    066         * @return the object managed by this initializer
    067         */
    068        public final T getObject() {
    069            return object;
    070        }
    071
    072        /**
    073         * Returns the object managed by this initializer. This implementation just
    074         * returns the object passed to the constructor.
    075         *
    076         * @return the object managed by this initializer
    077         * @throws ConcurrentException if an error occurs
    078         */
    079        public T get() throws ConcurrentException {
    080            return getObject();
    081        }
    082
    083        /**
    084         * Returns a hash code for this object. This implementation returns the hash
    085         * code of the managed object.
    086         *
    087         * @return a hash code for this object
    088         */
    089        @Override
    090        public int hashCode() {
    091            return getObject() != null ? getObject().hashCode() : 0;
    092        }
    093
    094        /**
    095         * Compares this object with another one. This implementation returns
    096         * <b>true</b> if and only if the passed in object is an instance of
    097         * {@code ConstantInitializer} which refers to an object equals to the
    098         * object managed by this instance.
    099         *
    100         * @param obj the object to compare to
    101         * @return a flag whether the objects are equal
    102         */
    103        @Override
    104        public boolean equals(Object obj) {
    105            if (this == obj) {
    106                return true;
    107            }
    108            if (!(obj instanceof ConstantInitializer<?>)) {
    109                return false;
    110            }
    111
    112            ConstantInitializer<?> c = (ConstantInitializer<?>) obj;
    113            return ObjectUtils.equals(getObject(), c.getObject());
    114        }
    115
    116        /**
    117         * Returns a string representation for this object. This string also
    118         * contains a string representation of the object managed by this
    119         * initializer.
    120         *
    121         * @return a string for this object
    122         */
    123        @Override
    124        public String toString() {
    125            return String.format(FMT_TO_STRING, Integer.valueOf(System.identityHashCode(this)),
    126                    String.valueOf(getObject()));
    127        }
    128    }