    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 *      https://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;
    022import java.util.Objects;
    023
    024import org.apache.commons.collections4.Transformer;
    025
    026/**
    027 * Decorates another {@link Collection} to transform objects that are added.
    028 * <p>
    029 * The add methods are affected by this class.
    030 * Thus objects must be removed or searched for using their transformed form.
    031 * For example, if the transformation converts Strings to Integers, you must
    032 * use the Integer form to remove objects.
    033 * </p>
    034 * <p>
    035 * This class is Serializable from Commons Collections 3.1.
    036 * </p>
    037 *
    038 * @param <E> The type of the elements in the collection.
    039 * @since 3.0
    040 */
    041public class TransformedCollection<E> extends AbstractCollectionDecorator<E> {
    042
    043    /** Serialization version */
    044    private static final long serialVersionUID = 8692300188161871514L;
    045
    046    /**
    047     * Creates a transforming collection that will transform
    048     * existing contents of the specified collection.
    049     * <p>
    050     * If there are any elements already in the collection being decorated, they
    051     * will be transformed by this method.
    052     * Contrast this with {@link #transformingCollection(Collection, Transformer)}.
    053     * </p>
    054     *
    055     * @param <E> The type of the elements in the collection.
    056     * @param collection  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> transformedCollection(final Collection<E> collection,
    063            final Transformer<? super E, ? extends E> transformer) {
    064
    065        final TransformedCollection<E> decorated = new TransformedCollection<>(collection, transformer);
    066        // null collection & transformer are disallowed by the constructor call above
    067        if (!collection.isEmpty()) {
    068            @SuppressWarnings("unchecked") // collection is of type E
    069            final E[] values = (E[]) collection.toArray(); // NOPMD - false positive for generics
    070            collection.clear();
    071            for (final E value : values) {
    072                decorated.decorated().add(transformer.apply(value));
    073            }
    074        }
    075        return decorated;
    076    }
    077
    078    /**
    079     * Creates a transforming collection.
    080     * <p>
    081     * If there are any elements already in the collection being decorated, they
    082     * are NOT transformed.
    083     * Contrast this with {@link #transformedCollection(Collection, Transformer)}.
    084     * </p>
    085     *
    086     * @param <E> The type of the elements in the collection.
    087     * @param coll  The collection to decorate, must not be null.
    088     * @param transformer  The transformer to use for conversion, must not be null.
    089     * @return A new transformed collection.
    090     * @throws NullPointerException if collection or transformer is null.
    091     * @since 4.0
    092     */
    093    public static <E> TransformedCollection<E> transformingCollection(final Collection<E> coll,
    094            final Transformer<? super E, ? extends E> transformer) {
    095        return new TransformedCollection<>(coll, transformer);
    096    }
    097
    098    /** The transformer to use */
    099    protected final Transformer<? super E, ? extends E> transformer;
    100
    101    /**
    102     * Constructs and wraps (not copies).
    103     * <p>
    104     * If there are any elements already in the collection being decorated, they
    105     * are NOT transformed.
    106     * </p>
    107     *
    108     * @param collection  The collection to decorate, must not be null.
    109     * @param transformer  The transformer to use for conversion, must not be null.
    110     * @throws NullPointerException if collection or transformer is null.
    111     */
    112    protected TransformedCollection(final Collection<E> collection, final Transformer<? super E, ? extends E> transformer) {
    113        super(collection);
    114        this.transformer = Objects.requireNonNull(transformer, "transformer");
    115    }
    116
    117    @Override
    118    public boolean add(final E object) {
    119        return decorated().add(transform(object));
    120    }
    121
    122    @Override
    123    public boolean addAll(final Collection<? extends E> coll) {
    124        return decorated().addAll(transform(coll));
    125    }
    126
    127    /**
    128     * Transforms a collection.
    129     * <p>
    130     * The transformer itself may throw an exception if necessary.
    131     * </p>
    132     *
    133     * @param coll  The collection to transform.
    134     * @return A transformed object.
    135     */
    136    protected Collection<E> transform(final Collection<? extends E> coll) {
    137        final List<E> list = new ArrayList<>(coll.size());
    138        for (final E item : coll) {
    139            list.add(transform(item));
    140        }
    141        return list;
    142    }
    143
    144    /**
    145     * Transforms an object.
    146     * <p>
    147     * The transformer itself may throw an exception if necessary.
    148     * </p>
    149     *
    150     * @param object  The object to transform.
    151     * @return A transformed object.
    152     */
    153    protected E transform(final E object) {
    154        return transformer.apply(object);
    155    }
    156
    157}