Java example source code file (ConstantInitializer.java)

This example Java source code file (ConstantInitializer.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

concurrentexception, concurrentinitializer, constantinitializer, fmt_to_string, object, override, string, suppresswarnings

The ConstantInitializer.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3.concurrent;

import org.apache.commons.lang3.ObjectUtils;

/**
 * <p>
 * A very simple implementation of the {@link ConcurrentInitializer} interface
 * which always returns the same object.
 * </p>
 * <p>
 * An instance of this class is passed a reference to an object when it is
 * constructed. The {@link #get()} method just returns this object. No
 * synchronization is required.
 * </p>
 * <p>
 * This class is useful for instance for unit testing or in cases where a
 * specific object has to be passed to an object which expects a
 * {@link ConcurrentInitializer}.
 * </p>
 *
 * @since 3.0
 * @param <T> the type of the object managed by this initializer
 */
public class ConstantInitializer<T> implements ConcurrentInitializer {
    /** Constant for the format of the string representation. */
    private static final String FMT_TO_STRING = "ConstantInitializer@%d [ object = %s ]";

    /** Stores the managed object. */
    private final T object;

    /**
     * Creates a new instance of {@code ConstantInitializer} and initializes it
     * with the object to be managed. The {@code get()} method will always
     * return the object passed here. This class does not place any restrictions
     * on the object. It may be <b>null, then {@code get()} will return
     * <b>null, too.
     *
     * @param obj the object to be managed by this initializer
     */
    public ConstantInitializer(final T obj) {
        object = obj;
    }

    /**
     * Directly returns the object that was passed to the constructor. This is
     * the same object as returned by {@code get()}. However, this method does
     * not declare that it throws an exception.
     *
     * @return the object managed by this initializer
     */
    public final T getObject() {
        return object;
    }

    /**
     * Returns the object managed by this initializer. This implementation just
     * returns the object passed to the constructor.
     *
     * @return the object managed by this initializer
     * @throws ConcurrentException if an error occurs
     */
    @Override
    public T get() throws ConcurrentException {
        return getObject();
    }

    /**
     * Returns a hash code for this object. This implementation returns the hash
     * code of the managed object.
     *
     * @return a hash code for this object
     */
    @Override
    public int hashCode() {
        return getObject() != null ? getObject().hashCode() : 0;
    }

    /**
     * Compares this object with another one. This implementation returns
     * <b>true if and only if the passed in object is an instance of
     * {@code ConstantInitializer} which refers to an object equals to the
     * object managed by this instance.
     *
     * @param obj the object to compare to
     * @return a flag whether the objects are equal
     */
    @SuppressWarnings( "deprecation" ) // ObjectUtils.equals(Object, Object) has been deprecated in 3.2
    @Override
    public boolean equals(final Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof ConstantInitializer<?>)) {
            return false;
        }

        final ConstantInitializer<?> c = (ConstantInitializer) obj;
        return ObjectUtils.equals(getObject(), c.getObject());
    }

    /**
     * Returns a string representation for this object. This string also
     * contains a string representation of the object managed by this
     * initializer.
     *
     * @return a string for this object
     */
    @Override
    public String toString() {
        return String.format(FMT_TO_STRING, Integer.valueOf(System.identityHashCode(this)),
                String.valueOf(getObject()));
    }
}