org.apache.commons.collections4.collection.TransformedCollection Maven / Gradle / Ivy
Show all versions of commons-collections4 Show documentation
/*
* 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.collection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.apache.commons.collections4.Transformer;
/**
* Decorates another {@link Collection} to transform objects that are added.
*
* The add methods are affected by this class.
* Thus objects must be removed or searched for using their transformed form.
* For example, if the transformation converts Strings to Integers, you must
* use the Integer form to remove objects.
*
* This class is Serializable from Commons Collections 3.1.
*
* @param the type of the elements in the collection
* @since 3.0
*/
public class TransformedCollection extends AbstractCollectionDecorator {
/** Serialization version */
private static final long serialVersionUID = 8692300188161871514L;
/** The transformer to use */
protected final Transformer transformer;
/**
* Factory method to create a transforming collection.
*
* If there are any elements already in the collection being decorated, they
* are NOT transformed.
* Contrast this with {@link #transformedCollection(Collection, Transformer)}.
*
* @param the type of the elements in the collection
* @param coll the collection to decorate, must not be null
* @param transformer the transformer to use for conversion, must not be null
* @return a new transformed collection
* @throws NullPointerException if collection or transformer is null
* @since 4.0
*/
public static TransformedCollection transformingCollection(final Collection coll,
final Transformer transformer) {
return new TransformedCollection<>(coll, transformer);
}
/**
* Factory method to create a transforming collection that will transform
* existing contents of the specified collection.
*
* If there are any elements already in the collection being decorated, they
* will be transformed by this method.
* Contrast this with {@link #transformingCollection(Collection, Transformer)}.
*
* @param the type of the elements in the collection
* @param collection the collection to decorate, must not be null
* @param transformer the transformer to use for conversion, must not be null
* @return a new transformed Collection
* @throws NullPointerException if collection or transformer is null
* @since 4.0
*/
public static TransformedCollection transformedCollection(final Collection collection,
final Transformer transformer) {
final TransformedCollection decorated = new TransformedCollection<>(collection, transformer);
// null collection & transformer are disallowed by the constructor call above
if (collection.size() > 0) {
@SuppressWarnings("unchecked") // collection is of type E
final E[] values = (E[]) collection.toArray(); // NOPMD - false positive for generics
collection.clear();
for (final E value : values) {
decorated.decorated().add(transformer.transform(value));
}
}
return decorated;
}
//-----------------------------------------------------------------------
/**
* Constructor that wraps (not copies).
*
* If there are any elements already in the collection being decorated, they
* are NOT transformed.
*
* @param coll the collection to decorate, must not be null
* @param transformer the transformer to use for conversion, must not be null
* @throws NullPointerException if collection or transformer is null
*/
protected TransformedCollection(final Collection coll, final Transformer transformer) {
super(coll);
if (transformer == null) {
throw new NullPointerException("Transformer must not be null");
}
this.transformer = transformer;
}
/**
* Transforms an object.
*
* The transformer itself may throw an exception if necessary.
*
* @param object the object to transform
* @return a transformed object
*/
protected E transform(final E object) {
return transformer.transform(object);
}
/**
* Transforms a collection.
*
* The transformer itself may throw an exception if necessary.
*
* @param coll the collection to transform
* @return a transformed object
*/
protected Collection transform(final Collection coll) {
final List list = new ArrayList<>(coll.size());
for (final E item : coll) {
list.add(transform(item));
}
return list;
}
//-----------------------------------------------------------------------
@Override
public boolean add(final E object) {
return decorated().add(transform(object));
}
@Override
public boolean addAll(final Collection coll) {
return decorated().addAll(transform(coll));
}
}