PredicateTransformer.java

/*
 * 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.collections4.functors;

import java.io.Serializable;

import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.Transformer;

/**
 * Transformer implementation that calls a Predicate using the input object
 * and then returns the result.
 *
 * @param <T> the type of the input and result to the function.
 * @since 3.0
 */
public class PredicateTransformer<T> implements Transformer<T, Boolean>, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = 5278818408044349346L;

    /**
     * Factory method that performs validation.
     *
     * @param <T>  the input type
     * @param predicate  the predicate to call, not null
     * @return the {@code predicate} transformer
     * @throws IllegalArgumentException if the predicate is null
     */
    public static <T> Transformer<T, Boolean> predicateTransformer(final Predicate<? super T> predicate) {
        if (predicate == null) {
            throw new IllegalArgumentException("Predicate must not be null");
        }
        return new PredicateTransformer<>(predicate);
    }

    /** The closure to wrap */
    private final Predicate<? super T> iPredicate;

    /**
     * Constructor that performs no validation.
     * Use {@code predicateTransformer} if you want that.
     *
     * @param predicate  the predicate to call, not null
     */
    public PredicateTransformer(final Predicate<? super T> predicate) {
        iPredicate = predicate;
    }

    /**
     * Gets the predicate.
     *
     * @return the predicate
     * @since 3.1
     */
    public Predicate<? super T> getPredicate() {
        return iPredicate;
    }

    /**
     * Transforms the input to result by calling a predicate.
     *
     * @param input  the input object to transform
     * @return the transformed result
     */
    @Override
    public Boolean transform(final T input) {
        return Boolean.valueOf(iPredicate.test(input));
    }

}