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.collections4.functors;
018
019import java.io.Serializable;
020
021import org.apache.commons.collections4.Factory;
022
023/**
024 * Factory implementation that returns the same constant each time.
025 * <p>
026 * No check is made that the object is immutable. In general, only immutable
027 * objects should use the constant factory. Mutable objects should
028 * use the prototype factory.
029 *
030 * @since 3.0
031 * @version $Id: ConstantFactory.html 972421 2015-11-14 20:00:04Z tn $
032 */
033public class ConstantFactory<T> implements Factory<T>, Serializable {
034
035    /** Serial version UID */
036    private static final long serialVersionUID = -3520677225766901240L;
037
038    /** Returns null each time */
039    @SuppressWarnings("rawtypes") // The null factory works for all object types
040    public static final Factory NULL_INSTANCE = new ConstantFactory<Object>(null);
041
042    /** The closures to call in turn */
043    private final T iConstant;
044
045    /**
046     * Factory method that performs validation.
047     *
048     * @param <T>  the type of the constant
049     * @param constantToReturn  the constant object to return each time in the factory
050     * @return the <code>constant</code> factory.
051     */
052    @SuppressWarnings("unchecked") // The null factory works for all object types
053    public static <T> Factory<T> constantFactory(final T constantToReturn) {
054        if (constantToReturn == null) {
055            return (Factory<T>) NULL_INSTANCE;
056        }
057        return new ConstantFactory<T>(constantToReturn);
058    }
059
060    /**
061     * Constructor that performs no validation.
062     * Use <code>constantFactory</code> if you want that.
063     *
064     * @param constantToReturn  the constant to return each time
065     */
066    public ConstantFactory(final T constantToReturn) {
067        super();
068        iConstant = constantToReturn;
069    }
070
071    /**
072     * Always return constant.
073     *
074     * @return the stored constant value
075     */
076    public T create() {
077        return iConstant;
078    }
079
080    /**
081     * Gets the constant.
082     *
083     * @return the constant
084     * @since 3.1
085     */
086    public T getConstant() {
087        return iConstant;
088    }
089
090}