/*
 * 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.Transformer;

Transformer implementation that returns the same constant each time.

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.

Since:
3.0/**
 * 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.
 * </p>
 *
 * @since 3.0
 */
public class ConstantTransformer<I, O> implements Transformer<I, O>, Serializable {

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

    
Returns null each time /** Returns null each time */
    @SuppressWarnings("rawtypes")
    public static final Transformer NULL_INSTANCE = new ConstantTransformer<>(null);

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

    
Get a typed null instance.
Type parameters:
<I> –  the input type
<O> –  the output type
Returns:
Transformer<I, O> that always returns null./**
     * Get a typed null instance.
     *
     * @param <I>  the input type
     * @param <O>  the output type
     * @return Transformer&lt;I, O&gt; that always returns null.
     */
    public static <I, O> Transformer<I, O> nullTransformer() {
        return NULL_INSTANCE;
    }

    
Transformer method that performs validation.
Params:
constantToReturn –  the constant object to return each time in the factory
Type parameters:
<I> –  the input type
<O> –  the output type
Returns:
the constant factory./**
     * Transformer method that performs validation.
     *
     * @param <I>  the input type
     * @param <O>  the output type
     * @param constantToReturn  the constant object to return each time in the factory
     * @return the <code>constant</code> factory.
     */
    public static <I, O> Transformer<I, O> constantTransformer(final O constantToReturn) {
        if (constantToReturn == null) {
            return nullTransformer();
        }
        return new ConstantTransformer<>(constantToReturn);
    }

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

    
Transforms the input by ignoring it and returning the stored constant instead.
Params:
input –  the input object which is ignored
Returns:
the stored constant/**
     * Transforms the input by ignoring it and returning the stored constant instead.
     *
     * @param input  the input object which is ignored
     * @return the stored constant
     */
    @Override
    public O transform(final I input) {
        return iConstant;
    }

    
Gets the constant.
Returns:
the constant
Since:
3.1/**
     * Gets the constant.
     *
     * @return the constant
     * @since 3.1
     */
    public O getConstant() {
        return iConstant;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof ConstantTransformer == false) {
            return false;
        }
        final Object otherConstant = ((ConstantTransformer<?, ?>) obj).getConstant();
        return otherConstant == getConstant() || otherConstant != null && otherConstant.equals(getConstant());
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public int hashCode() {
        int result = "ConstantTransformer".hashCode() << 2;
        if (getConstant() != null) {
            result |= getConstant().hashCode();
        }
        return result;
    }
}