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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

There is a newer version: 4.5.0-M1

/*
 * 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.
 *
 * @since 3.0
 */
public class PredicateTransformer implements Transformer, Serializable {

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

    /** The closure to wrap */
    private final Predicate iPredicate;

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

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

    /**
     * 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.evaluate(input));
    }

    /**
     * Gets the predicate.
     *
     * @return the predicate
     * @since 3.1
     */
    public Predicate getPredicate() {
        return iPredicate;
    }

}