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 */
017package org.apache.commons.lang3.concurrent;
018
019import 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 1436770 2013-01-22 07:09:45Z ggregory $
039 * @param <T> the type of the object managed by this initializer
040 */
041public 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(final 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    @Override
080    public T get() throws ConcurrentException {
081        return getObject();
082    }
083
084    /**
085     * Returns a hash code for this object. This implementation returns the hash
086     * code of the managed object.
087     *
088     * @return a hash code for this object
089     */
090    @Override
091    public int hashCode() {
092        return getObject() != null ? getObject().hashCode() : 0;
093    }
094
095    /**
096     * Compares this object with another one. This implementation returns
097     * <b>true</b> if and only if the passed in object is an instance of
098     * {@code ConstantInitializer} which refers to an object equals to the
099     * object managed by this instance.
100     *
101     * @param obj the object to compare to
102     * @return a flag whether the objects are equal
103     */
104    @Override
105    public boolean equals(final Object obj) {
106        if (this == obj) {
107            return true;
108        }
109        if (!(obj instanceof ConstantInitializer<?>)) {
110            return false;
111        }
112
113        final ConstantInitializer<?> c = (ConstantInitializer<?>) obj;
114        return ObjectUtils.equals(getObject(), c.getObject());
115    }
116
117    /**
118     * Returns a string representation for this object. This string also
119     * contains a string representation of the object managed by this
120     * initializer.
121     *
122     * @return a string for this object
123     */
124    @Override
125    public String toString() {
126        return String.format(FMT_TO_STRING, Integer.valueOf(System.identityHashCode(this)),
127                String.valueOf(getObject()));
128    }
129}