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 * </p>
030 *
031 * @since 3.0
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<>(null);
041
042    /**
043     * Factory method that performs validation.
044     *
045     * @param <T>  the type of the constant
046     * @param constantToReturn  the constant object to return each time in the factory
047     * @return the {@code constant} factory.
048     */
049    public static <T> Factory<T> constantFactory(final T constantToReturn) {
050        if (constantToReturn == null) {
051            return NULL_INSTANCE;
052        }
053        return new ConstantFactory<>(constantToReturn);
054    }
055
056    /** The closures to call in turn */
057    private final T iConstant;
058
059    /**
060     * Constructor that performs no validation.
061     * Use {@code constantFactory} if you want that.
062     *
063     * @param constantToReturn  the constant to return each time
064     */
065    public ConstantFactory(final T constantToReturn) {
066        iConstant = constantToReturn;
067    }
068
069    /**
070     * Always return constant.
071     *
072     * @return the stored constant value
073     */
074    @Override
075    public T create() {
076        return iConstant;
077    }
078
079    /**
080     * Gets the constant.
081     *
082     * @return the constant
083     * @since 3.1
084     */
085    public T getConstant() {
086        return iConstant;
087    }
088
089}