org.apache.commons.collections.functors.SwitchTransformer Maven / Gradle / Ivy
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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.collections.functors;
import java.io.Serializable;
import java.util.Iterator;
import java.util.Map;
import org.apache.commons.collections.Predicate;
import org.apache.commons.collections.Transformer;
/**
* Transformer implementation calls the transformer whose predicate returns true,
* like a switch statement.
*
* @since Commons Collections 3.0
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author Stephen Colebourne
*/
public class SwitchTransformer implements Transformer, Serializable {
/** Serial version UID */
private static final long serialVersionUID = -6404460890903469332L;
/** The tests to consider */
private final Predicate[] iPredicates;
/** The matching transformers to call */
private final Transformer[] iTransformers;
/** The default transformer to call if no tests match */
private final Transformer iDefault;
/**
* Factory method that performs validation and copies the parameter arrays.
*
* @param predicates array of predicates, cloned, no nulls
* @param transformers matching array of transformers, cloned, no nulls
* @param defaultTransformer the transformer to use if no match, null means return null
* @return the chained transformer
* @throws IllegalArgumentException if array is null
* @throws IllegalArgumentException if any element in the array is null
*/
public static Transformer getInstance(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
FunctorUtils.validate(predicates);
FunctorUtils.validate(transformers);
if (predicates.length != transformers.length) {
throw new IllegalArgumentException("The predicate and transformer arrays must be the same size");
}
if (predicates.length == 0) {
return (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
}
predicates = FunctorUtils.copy(predicates);
transformers = FunctorUtils.copy(transformers);
return new SwitchTransformer(predicates, transformers, defaultTransformer);
}
/**
* Create a new Transformer that calls one of the transformers depending
* on the predicates.
*
* The Map consists of Predicate keys and Transformer values. A transformer
* is called if its matching predicate returns true. Each predicate is evaluated
* until one returns true. If no predicates evaluate to true, the default
* transformer is called. The default transformer is set in the map with a
* null key. The ordering is that of the iterator() method on the entryset
* collection of the map.
*
* @param predicatesAndTransformers a map of predicates to transformers
* @return the switch transformer
* @throws IllegalArgumentException if the map is null
* @throws IllegalArgumentException if any transformer in the map is null
* @throws ClassCastException if the map elements are of the wrong type
*/
public static Transformer getInstance(Map predicatesAndTransformers) {
Transformer[] transformers = null;
Predicate[] preds = null;
if (predicatesAndTransformers == null) {
throw new IllegalArgumentException("The predicate and transformer map must not be null");
}
if (predicatesAndTransformers.size() == 0) {
return ConstantTransformer.NULL_INSTANCE;
}
// convert to array like this to guarantee iterator() ordering
Transformer defaultTransformer = (Transformer) predicatesAndTransformers.remove(null);
int size = predicatesAndTransformers.size();
if (size == 0) {
return (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
}
transformers = new Transformer[size];
preds = new Predicate[size];
int i = 0;
for (Iterator it = predicatesAndTransformers.entrySet().iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
preds[i] = (Predicate) entry.getKey();
transformers[i] = (Transformer) entry.getValue();
i++;
}
return new SwitchTransformer(preds, transformers, defaultTransformer);
}
/**
* Constructor that performs no validation.
* Use getInstance if you want that.
*
* @param predicates array of predicates, not cloned, no nulls
* @param transformers matching array of transformers, not cloned, no nulls
* @param defaultTransformer the transformer to use if no match, null means return null
*/
public SwitchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
super();
iPredicates = predicates;
iTransformers = transformers;
iDefault = (defaultTransformer == null ? ConstantTransformer.NULL_INSTANCE : defaultTransformer);
}
/**
* Transforms the input to result by calling the transformer whose matching
* predicate returns true.
*
* @param input the input object to transform
* @return the transformed result
*/
public Object transform(Object input) {
for (int i = 0; i < iPredicates.length; i++) {
if (iPredicates[i].evaluate(input) == true) {
return iTransformers[i].transform(input);
}
}
return iDefault.transform(input);
}
/**
* Gets the predicates, do not modify the array.
*
* @return the predicates
* @since Commons Collections 3.1
*/
public Predicate[] getPredicates() {
return iPredicates;
}
/**
* Gets the transformers, do not modify the array.
*
* @return the transformers
* @since Commons Collections 3.1
*/
public Transformer[] getTransformers() {
return iTransformers;
}
/**
* Gets the default transformer.
*
* @return the default transformer
* @since Commons Collections 3.1
*/
public Transformer getDefaultTransformer() {
return iDefault;
}
}