    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)),
    137                String.valueOf(getObject()));
    138    }
    139}