1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.functor.core.composite; 18 19 import java.io.Serializable; 20 21 import org.apache.commons.functor.BinaryFunction; 22 23 /** 24 * Transposes (swaps) the arguments to some other 25 * {@link BinaryFunction function}. 26 * For example, given a function <i>f</i> 27 * and the ordered pair of arguments <i>a</i>, 28 * <i>b</i>. 29 * {@link #evaluate evaluates} to 30 * <code>f.evaluate(b,a)</code>. 31 * <p> 32 * Note that although this class implements 33 * {@link Serializable}, a given instance will 34 * only be truly <code>Serializable</code> if the 35 * underlying functor is. Attempts to serialize 36 * an instance whose delegate is not 37 * <code>Serializable</code> will result in an exception. 38 * </p> 39 * @version $Revision: 1171154 $ $Date: 2011-09-15 17:58:38 +0200 (Thu, 15 Sep 2011) $ 40 * @author Rodney Waldhoff 41 */ 42 public class TransposedFunction<L, R, T> implements BinaryFunction<L, R, T>, Serializable { 43 /** 44 * serialVersionUID declaration. 45 */ 46 private static final long serialVersionUID = -5824252875453493940L; 47 // attributes 48 // ------------------------------------------------------------------------ 49 private final BinaryFunction<? super R, ? super L, ? extends T> function; 50 51 // constructor 52 // ------------------------------------------------------------------------ 53 /** 54 * Create a new TransposedFunction. 55 * @param function BinaryFunction to transpose. 56 */ 57 public TransposedFunction(BinaryFunction<? super R, ? super L, ? extends T> function) { 58 if (function == null) { 59 throw new IllegalArgumentException("BinaryFunction argument was null"); 60 } 61 this.function = function; 62 } 63 64 // functor interface 65 // ------------------------------------------------------------------------ 66 /** 67 * {@inheritDoc} 68 */ 69 public final T evaluate(L left, R right) { 70 return function.evaluate(right, left); 71 } 72 73 /** 74 * {@inheritDoc} 75 */ 76 public final boolean equals(Object that) { 77 return that == this || (that instanceof TransposedFunction<?, ?, ?> 78 && equals((TransposedFunction<?, ?, ?>) that)); 79 } 80 81 /** 82 * Learn whether another TransposedFunction is equal to this. 83 * @param that TransposedFunction to test 84 * @return boolean 85 */ 86 public final boolean equals(TransposedFunction<?, ?, ?> that) { 87 return null != that && (null == function ? null == that.function : function.equals(that.function)); 88 } 89 90 /** 91 * {@inheritDoc} 92 */ 93 public int hashCode() { 94 int hash = "TransposedFunction".hashCode(); 95 if (null != function) { 96 hash ^= function.hashCode(); 97 } 98 return hash; 99 } 100 101 /** 102 * {@inheritDoc} 103 */ 104 public String toString() { 105 return "TransposedFunction<" + function + ">"; 106 } 107 108 // static 109 // ------------------------------------------------------------------------ 110 /** 111 * Transpose a BinaryFunction. 112 * @param f BinaryFunction to transpose 113 * @return TransposedFunction 114 */ 115 public static <L, R, T> TransposedFunction<R, L, T> transpose(BinaryFunction<? super L, ? super R, ? extends T> f) { 116 return null == f ? null : new TransposedFunction<R, L, T>(f); 117 } 118 119 }