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/*
* 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
*/
public class ConstantTransformer implements Transformer, Serializable {
/** Serial version UID */
private static final long serialVersionUID = 6374440726369055124L;
/** Returns null each time */
@SuppressWarnings("rawtypes")
public static final Transformer NULL_INSTANCE = new ConstantTransformer<>(null);
/** The closures to call in turn */
private final O iConstant;
/**
* Get a typed null instance.
*
* @param the input type
* @param the output type
* @return Transformer<I, O> that always returns null.
*/
@SuppressWarnings("unchecked") // The null transformer works for all object types
public static Transformer nullTransformer() {
return NULL_INSTANCE;
}
/**
* Transformer method that performs validation.
*
* @param the input type
* @param the output type
* @param constantToReturn the constant object to return each time in the factory
* @return the constant factory.
*/
public static Transformer constantTransformer(final O constantToReturn) {
if (constantToReturn == null) {
return nullTransformer();
}
return new ConstantTransformer<>(constantToReturn);
}
/**
* Constructor that performs no validation.
* Use constantTransformer 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.
*
* @param input the input object which is ignored
* @return the stored constant
*/
@Override
public O transform(final I input) {
return iConstant;
}
/**
* Gets the constant.
*
* @return the constant
* @since 3.1
*/
public O getConstant() {
return iConstant;
}
/**
* {@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}
*/
@Override
public int hashCode() {
int result = "ConstantTransformer".hashCode() << 2;
if (getConstant() != null) {
result |= getConstant().hashCode();
}
return result;
}
}