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 * @param <T> the type of results supplied by this supplier.
032 * @since 3.0
033 */
034public class ConstantFactory<T> implements Factory<T>, Serializable {
035
036    /** Serial version UID */
037    private static final long serialVersionUID = -3520677225766901240L;
038
039    /** Returns null each time */
040    @SuppressWarnings("rawtypes") // The null factory works for all object types
041    public static final Factory NULL_INSTANCE = new ConstantFactory<>(null);
042
043    /**
044     * Factory method that performs validation.
045     *
046     * @param <T>  the type of the constant
047     * @param constantToReturn  the constant object to return each time in the factory
048     * @return the {@code constant} factory.
049     */
050    public static <T> Factory<T> constantFactory(final T constantToReturn) {
051        if (constantToReturn == null) {
052            return NULL_INSTANCE;
053        }
054        return new ConstantFactory<>(constantToReturn);
055    }
056
057    /** The closures to call in turn */
058    private final T iConstant;
059
060    /**
061     * Constructor that performs no validation.
062     * Use {@code constantFactory} if you want that.
063     *
064     * @param constantToReturn  the constant to return each time
065     */
066    public ConstantFactory(final T constantToReturn) {
067        iConstant = constantToReturn;
068    }
069
070    /**
071     * Always return constant.
072     *
073     * @return the stored constant value
074     */
075    @Override
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}