org.apache.commons.collections15.functors.ConstantTransformer.java Source code

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Here is the source code for org.apache.commons.collections15.functors.ConstantTransformer.java

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// GenericsNote: Converted.
/*
 *  Copyright 2001-2004 The Apache Software Foundation
 *
 *  Licensed 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.collections15.functors;

import org.apache.commons.collections15.Transformer;

import java.io.Serializable;

/**
 * Transformer implementation that returns the same constant each time.
 * <p/>
 * No check is made that the object is immutable. In general, only immutable
 * objects should use the constant factory. Mutable objects should
 * use the prototype factory.
 *
 * @author Matt Hall, John Watkinson, Stephen Colebourne
 * @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:24 $
 * @since Commons Collections 3.0
 */
public class ConstantTransformer<T> implements Transformer<Object, T>, Serializable {

    /**
     * Serial version UID
     */
    static final long serialVersionUID = 6374440726369055124L;

    /**
     * Returns null each time
     */
    public static final Transformer NULL_INSTANCE = new ConstantTransformer(null);

    /**
     * The closures to call in turn
     */
    private final T iConstant;

    /**
     * Transformer method that performs validation.
     *
     * @param constantToReturn the constant object to return each time in the factory
     * @return the <code>constant</code> factory.
     */
    public static <T> Transformer<Object, T> getInstance(T constantToReturn) {
        if (constantToReturn == null) {
            return NULL_INSTANCE;
        }
        return new ConstantTransformer<T>(constantToReturn);
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance</code> if you want that.
     *
     * @param constantToReturn the constant to return each time
     */
    public ConstantTransformer(T constantToReturn) {
        super();
        iConstant = constantToReturn;
    }

    /**
     * Transforms the input by ignoring it and returning the stored constant instead.
     *
     * @param input the input object which is ignored
     * @return the stored constant
     */
    public T transform(Object input) {
        return iConstant;
    }

    /**
     * Gets the constant.
     *
     * @return the constant
     * @since Commons Collections 3.1
     */
    public T getConstant() {
        return iConstant;
    }

}