    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}