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    }