Java tutorial
/* * Copyright 2001-2004 The Apache Software Foundation * * Licensed 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.collections.functors; import java.io.Serializable; import org.apache.commons.collections.Transformer; /** * Transformer implementation that returns the same constant each time. * <p> * No check is made that the object is immutable. In general, only immutable * objects should use the constant factory. Mutable objects should * use the prototype factory. * * @since Commons Collections 3.0 * @version $Revision: 1.5 $ $Date: 2004/05/16 11:36:31 $ * * @author Stephen Colebourne */ public class ConstantTransformer implements Transformer, Serializable { /** Serial version UID */ static final long serialVersionUID = 6374440726369055124L; /** Returns null each time */ public static final Transformer NULL_INSTANCE = new ConstantTransformer(null); /** The closures to call in turn */ private final Object iConstant; /** * Transformer method that performs validation. * * @param constantToReturn the constant object to return each time in the factory * @return the <code>constant</code> factory. */ public static Transformer getInstance(Object constantToReturn) { if (constantToReturn == null) { return NULL_INSTANCE; } return new ConstantTransformer(constantToReturn); } /** * Constructor that performs no validation. * Use <code>getInstance</code> if you want that. * * @param constantToReturn the constant to return each time */ public ConstantTransformer(Object constantToReturn) { super(); iConstant = constantToReturn; } /** * Transforms the input by ignoring it and returning the stored constant instead. * * @param input the input object which is ignored * @return the stored constant */ public Object transform(Object input) { return iConstant; } /** * Gets the constant. * * @return the constant * @since Commons Collections 3.1 */ public Object getConstant() { return iConstant; } }