| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.functor.core.composite; |
| |
| import java.io.Serializable; |
| |
| import org.apache.commons.functor.Function; |
| import org.apache.commons.lang3.Validate; |
| |
| /** |
| * A {@link Function Function} |
| * representing the composition of |
| * {@link Function Functions}, |
| * "chaining" the output of one to the input |
| * of another. For example, |
| * <pre>new CompositeFunction(f).of(g)</pre> |
| * {@link #evaluate evaluates} to |
| * <code>f.evaluate(g.evaluate(obj))</code>, and |
| * <pre>new CompositeFunction(f).of(g).of(h)</pre> |
| * {@link #evaluate evaluates} to |
| * <code>f.evaluate(g.evaluate(h.evaluate(obj)))</code>. |
| * <p> |
| * When the collection is empty, this function is |
| * an identity function. |
| * </p> |
| * <p> |
| * Note that although this class implements |
| * {@link Serializable}, a given instance will |
| * only be truly <code>Serializable</code> if all the |
| * underlying functors are. Attempts to serialize |
| * an instance whose delegates are not all |
| * <code>Serializable</code> will result in an exception. |
| * </p> |
| * @param <A> the argument type. |
| * @param <T> the returned value type. |
| * @version $Revision: 1365329 $ $Date: 2012-07-24 19:34:23 -0300 (Tue, 24 Jul 2012) $ |
| */ |
| public class CompositeFunction<A, T> implements Function<A, T>, Serializable { |
| |
| /** |
| * serialVersionUID declaration. |
| */ |
| private static final long serialVersionUID = 4945193629275757281L; |
| |
| /** Base hash integer used to shift hash. */ |
| private static final int HASH_SHIFT = 4; |
| |
| /** |
| * Encapsulates a double function evaluation. |
| * @param <A> argument type |
| * @param <X> intermediate type |
| * @param <T> return type |
| */ |
| private static class Helper<X, A, T> implements Function<A, T>, Serializable { |
| /** |
| * serialVersionUID declaration. |
| */ |
| private static final long serialVersionUID = 8167255331321876718L; |
| /** |
| * The last evaluator function. |
| */ |
| private Function<? super X, ? extends T> following; |
| /** |
| * The first evaluator function. |
| */ |
| private Function<? super A, ? extends X> preceding; |
| |
| /** |
| * Create a new Helper. |
| * @param following Function<X, Y> |
| * @param preceding Function<Y, Z> |
| */ |
| public Helper(Function<? super X, ? extends T> following, |
| Function<? super A, ? extends X> preceding) { |
| this.following = Validate.notNull(following, "Function argument must not be null"); |
| this.preceding = Validate.notNull(preceding, "Function argument must not be null"); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| public T evaluate(A obj) { |
| return following.evaluate(preceding.evaluate(obj)); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public boolean equals(Object obj) { |
| return obj == this || obj instanceof Helper<?, ?, ?> && equals((Helper<?, ?, ?>) obj); |
| } |
| |
| /** |
| * Checks if input helper is equals to this instance. |
| * |
| * @param helper the helper to check |
| * @return true, if helpers are equals, false otherwise |
| */ |
| private boolean equals(Helper<?, ?, ?> helper) { |
| return helper.following.equals(following) && helper.preceding.equals(preceding); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public int hashCode() { |
| int result = "CompositeFunction$Helper".hashCode(); |
| result <<= 2; |
| result ^= following.hashCode(); |
| result <<= 2; |
| result ^= preceding.hashCode(); |
| return result; |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public String toString() { |
| return following.toString() + " of " + preceding.toString(); |
| } |
| } |
| |
| /** |
| * The adapted function. |
| */ |
| private final Function<? super A, ? extends T> function; |
| |
| /** |
| * Create a new CompositeFunction. |
| * @param function Function to call |
| */ |
| public CompositeFunction(Function<? super A, ? extends T> function) { |
| this.function = Validate.notNull(function, "function must not be null"); |
| } |
| |
| /** |
| * Creates a new {@link CompositeFunction} instance given the input functions. |
| * |
| * @param <X> the argument type. |
| * @param following The first evaluator function. |
| * @param preceding The last evaluator function. |
| */ |
| private <X> CompositeFunction(Function<? super X, ? extends T> following, |
| Function<? super A, ? extends X> preceding) { |
| this.function = new Helper<X, A, T>(following, preceding); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| public final T evaluate(A obj) { |
| return function.evaluate(obj); |
| } |
| |
| /** |
| * Fluently obtain a CompositeFunction that is "this function" applied to the specified preceding function. |
| * @param <P> argument type of the resulting function. |
| * @param preceding Function |
| * @return CompositeFunction<P, T> |
| */ |
| public final <P> CompositeFunction<P, T> of(Function<? super P, ? extends A> preceding) { |
| Validate.notNull(preceding, "preceding function was null"); |
| return new CompositeFunction<P, T>(function, preceding); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public final boolean equals(Object obj) { |
| if (obj == this) { |
| return true; |
| } |
| if (!(obj instanceof CompositeFunction<?, ?>)) { |
| return false; |
| } |
| CompositeFunction<?, ?> that = (CompositeFunction<?, ?>) obj; |
| return this.function.equals(that.function); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public int hashCode() { |
| // by construction, list is never null |
| return ("CompositeFunction".hashCode() << HASH_SHIFT) ^ function.hashCode(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public String toString() { |
| return "CompositeFunction<" + function + ">"; |
| } |
| |
| } |