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.functor.adapter;
018
019import org.apache.commons.functor.NullaryFunction;
020import org.apache.commons.functor.Function;
021import org.apache.commons.lang3.Validate;
022
023/**
024 * Adapts a
025 * {@link Function Function}
026 * to the
027 * {@link NullaryFunction NullaryFunction} interface
028 * using a constant unary argument.
029 *
030 * @param <T> the returned value type.
031 * @version $Revision: 1345136 $ $Date: 2012-06-01 09:47:06 -0300 (Fri, 01 Jun 2012) $
032 */
033public final class BoundNullaryFunction<T> implements NullaryFunction<T> {
034    /** The {@link Function Function} I'm wrapping. */
035    private final Function<Object, ? extends T> function;
036    /** The argument to pass to {@code function}. */
037    private final Object arg;
038
039    /**
040     * Create a new BoundNullaryFunction instance.
041     * @param <A> the argument value type
042     * @param function the function to adapt
043     * @param arg the constant argument to use
044     */
045    @SuppressWarnings("unchecked")
046    public <A> BoundNullaryFunction(Function<? super A, ? extends T> function, A arg) {
047        this.function =
048            (Function<Object, ? extends T>) Validate.notNull(function,
049                "Function argument was null");
050        this.arg = arg;
051    }
052
053    /**
054     * {@inheritDoc}
055     */
056    public T evaluate() {
057        return function.evaluate(arg);
058    }
059
060    /**
061     * {@inheritDoc}
062     */
063    @Override
064    public boolean equals(Object obj) {
065        if (obj == this) {
066            return true;
067        }
068        if (!(obj instanceof BoundNullaryFunction<?>)) {
069            return false;
070        }
071        BoundNullaryFunction<?> that = (BoundNullaryFunction<?>) obj;
072        if (!(that.function.equals(this.function))) {
073            return false;
074        }
075        return that.arg == this.arg || that.arg != null && that.arg.equals(this.arg);
076    }
077
078    /**
079     * {@inheritDoc}
080     */
081    @Override
082    public int hashCode() {
083        int result = "BoundNullaryFunction".hashCode();
084        result <<= 2;
085        result |= function.hashCode();
086        result <<= 2;
087        return arg == null ? result : result | arg.hashCode();
088    }
089
090    /**
091     * {@inheritDoc}
092     */
093    @Override
094    public String toString() {
095        return "BoundNullaryFunction<" + function.toString() + "(" + arg + ")>";
096    }
097
098    /**
099     * Adapt the given, possibly-<code>null</code>,
100     * {@link Function Function} to the
101     * {@link NullaryFunction NullaryFunction} interface by binding
102     * the specified <code>Object</code> as a constant
103     * argument.
104     * When the given <code>Function</code> is <code>null</code>,
105     * returns <code>null</code>.
106     * @param <A> input type
107     * @param <T> result type
108     * @param function the possibly-<code>null</code>
109     *        {@link Function Function} to adapt
110     * @param arg the object to bind as a constant argument
111     * @return a <code>BoundNullaryFunction</code> wrapping the given
112     *         {@link Function Function}, or <code>null</code>
113     *         if the given <code>Function</code> is <code>null</code>
114     */
115    public static <A, T> BoundNullaryFunction<T> bind(Function<? super A, ? extends T> function, A arg) {
116        return null == function ? null : new BoundNullaryFunction<T>(function, arg);
117    }
118
119}