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 java.util.Objects;
020
021/**
022 * A very simple implementation of the {@link ConcurrentInitializer} interface
023 * which always returns the same object.
024 *
025 * <p>
026 * An instance of this class is passed a reference to an object when it is
027 * constructed. The {@link #get()} method just returns this object. No
028 * synchronization is required.
029 * </p>
030 * <p>
031 * This class is useful for instance for unit testing or in cases where a
032 * specific object has to be passed to an object which expects a
033 * {@link ConcurrentInitializer}.
034 * </p>
035 *
036 * @since 3.0
037 * @param <T> the type of the object managed by this initializer
038 */
039public class ConstantInitializer<T> implements ConcurrentInitializer<T> {
040
041    /** Constant for the format of the string representation. */
042    private static final String FMT_TO_STRING = "ConstantInitializer@%d [ object = %s ]";
043
044    /** Stores the managed object. */
045    private final T object;
046
047    /**
048     * Creates a new instance of {@link ConstantInitializer} and initializes it
049     * with the object to be managed. The {@code get()} method will always
050     * return the object passed here. This class does not place any restrictions
051     * on the object. It may be <b>null</b>, then {@code get()} will return
052     * <b>null</b>, too.
053     *
054     * @param obj the object to be managed by this initializer
055     */
056    public ConstantInitializer(final T obj) {
057        object = obj;
058    }
059
060    /**
061     * Compares this object with another one. This implementation returns
062     * <b>true</b> if and only if the passed in object is an instance of
063     * {@link ConstantInitializer} which refers to an object equals to the
064     * object managed by this instance.
065     *
066     * @param obj the object to compare to
067     * @return a flag whether the objects are equal
068     */
069    @Override
070    public boolean equals(final Object obj) {
071        if (this == obj) {
072            return true;
073        }
074        if (!(obj instanceof ConstantInitializer<?>)) {
075            return false;
076        }
077
078        final ConstantInitializer<?> c = (ConstantInitializer<?>) obj;
079        return Objects.equals(getObject(), c.getObject());
080    }
081
082    /**
083     * Returns the object managed by this initializer. This implementation just
084     * returns the object passed to the constructor.
085     *
086     * @return the object managed by this initializer
087     * @throws ConcurrentException if an error occurs
088     */
089    @Override
090    public T get() throws ConcurrentException {
091        return getObject();
092    }
093
094    /**
095     * Directly returns the object that was passed to the constructor. This is
096     * the same object as returned by {@code get()}. However, this method does
097     * not declare that it throws an exception.
098     *
099     * @return the object managed by this initializer
100     */
101    public final T getObject() {
102        return object;
103    }
104
105    /**
106     * Returns a hash code for this object. This implementation returns the hash
107     * code of the managed object.
108     *
109     * @return a hash code for this object
110     */
111    @Override
112    public int hashCode() {
113        return Objects.hashCode(object);
114    }
115
116    /**
117     * As a {@link ConstantInitializer} is initialized on construction this will
118     * always return true.
119     *
120     * @return true.
121     * @since 3.14.0
122     */
123    public boolean isInitialized() {
124        return true;
125    }
126
127    /**
128     * Returns a string representation for this object. This string also
129     * contains a string representation of the object managed by this
130     * initializer.
131     *
132     * @return a string for this object
133     */
134    @Override
135    public String toString() {
136        return String.format(FMT_TO_STRING, Integer.valueOf(System.identityHashCode(this)), getObject());
137    }
138}