    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.collection;
    018
    019import java.util.ArrayList;
    020import java.util.Collection;
    021import java.util.List;
    022
    023import org.apache.commons.collections4.Transformer;
    024
    025/**
    026 * Decorates another {@link Collection} to transform objects that are added.
    027 * <p>
    028 * The add methods are affected by this class.
    029 * Thus objects must be removed or searched for using their transformed form.
    030 * For example, if the transformation converts Strings to Integers, you must
    031 * use the Integer form to remove objects.
    032 * </p>
    033 * <p>
    034 * This class is Serializable from Commons Collections 3.1.
    035 * </p>
    036 *
    037 * @param <E> the type of the elements in the collection
    038 * @since 3.0
    039 */
    040public class TransformedCollection<E> extends AbstractCollectionDecorator<E> {
    041
    042    /** Serialization version */
    043    private static final long serialVersionUID = 8692300188161871514L;
    044
    045    /** The transformer to use */
    046    protected final Transformer<? super E, ? extends E> transformer;
    047
    048    /**
    049     * Factory method to create a transforming collection.
    050     * <p>
    051     * If there are any elements already in the collection being decorated, they
    052     * are NOT transformed.
    053     * Contrast this with {@link #transformedCollection(Collection, Transformer)}.
    054     *
    055     * @param <E> the type of the elements in the collection
    056     * @param coll  the collection to decorate, must not be null
    057     * @param transformer  the transformer to use for conversion, must not be null
    058     * @return a new transformed collection
    059     * @throws NullPointerException if collection or transformer is null
    060     * @since 4.0
    061     */
    062    public static <E> TransformedCollection<E> transformingCollection(final Collection<E> coll,
    063            final Transformer<? super E, ? extends E> transformer) {
    064        return new TransformedCollection<>(coll, transformer);
    065    }
    066
    067    /**
    068     * Factory method to create a transforming collection that will transform
    069     * existing contents of the specified collection.
    070     * <p>
    071     * If there are any elements already in the collection being decorated, they
    072     * will be transformed by this method.
    073     * Contrast this with {@link #transformingCollection(Collection, Transformer)}.
    074     *
    075     * @param <E> the type of the elements in the collection
    076     * @param collection  the collection to decorate, must not be null
    077     * @param transformer  the transformer to use for conversion, must not be null
    078     * @return a new transformed Collection
    079     * @throws NullPointerException if collection or transformer is null
    080     * @since 4.0
    081     */
    082    public static <E> TransformedCollection<E> transformedCollection(final Collection<E> collection,
    083            final Transformer<? super E, ? extends E> transformer) {
    084
    085        final TransformedCollection<E> decorated = new TransformedCollection<>(collection, transformer);
    086        // null collection & transformer are disallowed by the constructor call above
    087        if (collection.size() > 0) {
    088            @SuppressWarnings("unchecked") // collection is of type E
    089            final E[] values = (E[]) collection.toArray(); // NOPMD - false positive for generics
    090            collection.clear();
    091            for (final E value : values) {
    092                decorated.decorated().add(transformer.transform(value));
    093            }
    094        }
    095        return decorated;
    096    }
    097
    098    //-----------------------------------------------------------------------
    099    /**
    100     * Constructor that wraps (not copies).
    101     * <p>
    102     * If there are any elements already in the collection being decorated, they
    103     * are NOT transformed.
    104     *
    105     * @param coll  the collection to decorate, must not be null
    106     * @param transformer  the transformer to use for conversion, must not be null
    107     * @throws NullPointerException if collection or transformer is null
    108     */
    109    protected TransformedCollection(final Collection<E> coll, final Transformer<? super E, ? extends E> transformer) {
    110        super(coll);
    111        if (transformer == null) {
    112            throw new NullPointerException("Transformer must not be null");
    113        }
    114        this.transformer = transformer;
    115    }
    116
    117    /**
    118     * Transforms an object.
    119     * <p>
    120     * The transformer itself may throw an exception if necessary.
    121     *
    122     * @param object  the object to transform
    123     * @return a transformed object
    124     */
    125    protected E transform(final E object) {
    126        return transformer.transform(object);
    127    }
    128
    129    /**
    130     * Transforms a collection.
    131     * <p>
    132     * The transformer itself may throw an exception if necessary.
    133     *
    134     * @param coll  the collection to transform
    135     * @return a transformed object
    136     */
    137    protected Collection<E> transform(final Collection<? extends E> coll) {
    138        final List<E> list = new ArrayList<>(coll.size());
    139        for (final E item : coll) {
    140            list.add(transform(item));
    141        }
    142        return list;
    143    }
    144
    145    //-----------------------------------------------------------------------
    146    @Override
    147    public boolean add(final E object) {
    148        return decorated().add(transform(object));
    149    }
    150
    151    @Override
    152    public boolean addAll(final Collection<? extends E> coll) {
    153        return decorated().addAll(transform(coll));
    154    }
    155
    156}