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 */
017 package org.apache.commons.functor.adapter;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.functor.BinaryFunction;
022 import org.apache.commons.functor.UnaryFunction;
023
024 /**
025 * Adapts a
026 * {@link BinaryFunction BinaryFunction}
027 * to the
028 * {@link UnaryFunction UnaryFunction} interface
029 * using a constant left-side argument.
030 * <p/>
031 * Note that although this class implements
032 * {@link Serializable}, a given instance will
033 * only be truly <code>Serializable</code> if the
034 * underlying objects are. Attempts to serialize
035 * an instance whose delegates are not
036 * <code>Serializable</code> will result in an exception.
037 *
038 * @param <A> the argument type.
039 * @param <T> the returned value type.
040 * @version $Revision: 1157618 $ $Date: 2011-08-14 21:54:43 +0200 (Sun, 14 Aug 2011) $
041 * @author Rodney Waldhoff
042 */
043 public final class LeftBoundFunction<A, T> implements UnaryFunction<A, T>, Serializable {
044 /**
045 * serialVersionUID declaration.
046 */
047 private static final long serialVersionUID = -7456827102718911769L;
048 /** The {@link BinaryFunction BinaryFunction} I'm wrapping. */
049 private final BinaryFunction<Object, ? super A, ? extends T> function;
050 /** The parameter to pass to {@code function}. */
051 private final Object param;
052
053 /**
054 * Create a new LeftBoundFunction instance.
055 * @param <L> bound arg type
056 * @param function the function to adapt
057 * @param arg the constant argument to use
058 */
059 @SuppressWarnings("unchecked")
060 public <L> LeftBoundFunction(BinaryFunction<? super L, ? super A, ? extends T> function, L arg) {
061 if (function == null) {
062 throw new IllegalArgumentException("BinaryFunction argument was null");
063 }
064 this.function = (BinaryFunction<Object, ? super A, ? extends T>) function;
065 this.param = arg;
066 }
067
068 /**
069 * {@inheritDoc}
070 */
071 public T evaluate(A obj) {
072 return function.evaluate(param, obj);
073 }
074
075 /**
076 * {@inheritDoc}
077 */
078 public boolean equals(Object that) {
079 return that == this || (that instanceof LeftBoundFunction<?, ?> && equals((LeftBoundFunction<?, ?>) that));
080 }
081
082 /**
083 * Learn whether another LeftBoundFunction is equal to this.
084 * @param that LeftBoundFunction to test
085 * @return boolean
086 */
087 public boolean equals(LeftBoundFunction<?, ?> that) {
088 return null != that
089 && (null == function ? null == that.function : function.equals(that.function))
090 && (null == param ? null == that.param : param.equals(that.param));
091 }
092
093 /**
094 * {@inheritDoc}
095 */
096 public int hashCode() {
097 int hash = "LeftBoundFunction".hashCode();
098 if (null != function) {
099 hash <<= 2;
100 hash ^= function.hashCode();
101 }
102 if (null != param) {
103 hash <<= 2;
104 hash ^= param.hashCode();
105 }
106 return hash;
107 }
108
109 /**
110 * {@inheritDoc}
111 */
112 public String toString() {
113 return "LeftBoundFunction<" + function + "(" + param + ",?)>";
114 }
115
116 /**
117 * Adapt a BinaryFunction as a UnaryFunction.
118 * @param <L> left type
119 * @param <R> right type
120 * @param <T> result type
121 * @param function to adapt
122 * @param arg left side argument
123 * @return LeftBoundFunction
124 */
125 public static <L, R, T> LeftBoundFunction<R, T> bind(
126 BinaryFunction<? super L, ? super R, ? extends T> function, L arg) {
127 return null == function ? null : new LeftBoundFunction<R, T>(function, arg);
128 }
129
130 }