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    }