src/main/java/org/apache/commons/collections4/list/GrowthList.java

/*
 * 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.list;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

/**
 * Decorates another {@code List} to make it seamlessly grow when
 * indices larger than the list size are used on add and set,
 * avoiding most IndexOutOfBoundsExceptions.
 * <p>
 * This class avoids errors by growing when a set or add method would
 * normally throw an IndexOutOfBoundsException.
 * Note that IndexOutOfBoundsException IS returned for invalid negative indices.
 * </p>
 * <p>
 * Trying to set or add to an index larger than the size will cause the list
 * to grow (using {@code null} elements). Clearly, care must be taken
 * not to use excessively large indices, as the internal list will grow to
 * match.
 * </p>
 * <p>
 * Trying to use any method other than add or set with an invalid index will
 * call the underlying list and probably result in an IndexOutOfBoundsException.
 * </p>
 * <p>
 * Take care when using this list with {@code null} values, as
 * {@code null} is the value added when growing the list.
 * </p>
 * <p>
 * All sub-lists will access the underlying list directly, and will throw
 * IndexOutOfBoundsExceptions.
 * </p>
 * <p>
 * This class differs from {@link LazyList} because here growth occurs on
 * set and add, where {@code LazyList} grows on get. However, they
 * can be used together by decorating twice.
 * </p>
 *
 * @see LazyList
 * @since 3.2
 */
public class GrowthList<E> extends AbstractSerializableListDecorator<E> {

    /** Serialization version */
    private static final long serialVersionUID = -3620001881672L;

    /**
     * Factory method to create a growth list.
     *
     * @param <E> the type of the elements in the list
     * @param list  the list to decorate, must not be null
     * @return a new growth list
     * @throws NullPointerException if list is null
     * @since 4.0
     */
    public static <E> GrowthList<E> growthList(final List<E> list) {
        return new GrowthList<>(list);
    }

    //-----------------------------------------------------------------------
    /**
     * Constructor that uses an ArrayList internally.
     */
    public GrowthList() {
        super(new ArrayList<E>());
    }

    /**
     * Constructor that uses an ArrayList internally.
     *
     * @param initialCapacity  the initial capacity of the ArrayList
     * @throws IllegalArgumentException if initial capacity is invalid
     */
    public GrowthList(final int initialCapacity) {
        super(new ArrayList<E>(initialCapacity));
    }

    /**
     * Constructor that wraps (not copies).
     *
     * @param list  the list to decorate, must not be null
     * @throws NullPointerException if list is null
     */
    protected GrowthList(final List<E> list) {
        super(list);
    }

    //-----------------------------------------------------------------------
    /**
     * Decorate the add method to perform the growth behavior.
     * <p>
     * If the requested index is greater than the current size, the list will
     * grow to the new size. Indices between the old size and the requested
     * size will be filled with {@code null}.
     * <p>
     * If the index is less than the current size, the value will be added to
     * the underlying list directly.
     * If the index is less than zero, the underlying list is called, which
     * will probably throw an IndexOutOfBoundsException.
     *
     * @param index  the index to add at
     * @param element  the object to add at the specified index
     * @throws UnsupportedOperationException if the underlying list doesn't implement set
     * @throws ClassCastException if the underlying list rejects the element
     * @throws IllegalArgumentException if the underlying list rejects the element
     */
    @Override
    public void add(final int index, final E element) {
        final int size = decorated().size();
        if (index > size) {
            decorated().addAll(Collections.<E>nCopies(index - size, null));
        }
        decorated().add(index, element);
    }

    //-----------------------------------------------------------------------
    /**
     * Decorate the addAll method to perform the growth behavior.
     * <p>
     * If the requested index is greater than the current size, the list will
     * grow to the new size. Indices between the old size and the requested
     * size will be filled with {@code null}.
     * <p>
     * If the index is less than the current size, the values will be added to
     * the underlying list directly.
     * If the index is less than zero, the underlying list is called, which
     * will probably throw an IndexOutOfBoundsException.
     *
     * @param index  the index to add at
     * @param coll  the collection to add at the specified index
     * @return true if the list changed
     * @throws UnsupportedOperationException if the underlying list doesn't implement set
     * @throws ClassCastException if the underlying list rejects the element
     * @throws IllegalArgumentException if the underlying list rejects the element
     */
    @Override
    public boolean addAll(final int index, final Collection<? extends E> coll) {
        final int size = decorated().size();
        boolean result = false;
        if (index > size) {
            decorated().addAll(Collections.<E>nCopies(index - size, null));
            result = true;
        }
        return decorated().addAll(index, coll) || result;
    }

    //-----------------------------------------------------------------------
    /**
     * Decorate the set method to perform the growth behavior.
     * <p>
     * If the requested index is greater than the current size, the list will
     * grow to the new size. Indices between the old size and the requested
     * size will be filled with {@code null}.
     * <p>
     * If the index is less than the current size, the value will be set onto
     * the underlying list directly.
     * If the index is less than zero, the underlying list is called, which
     * will probably throw an IndexOutOfBoundsException.
     *
     * @param index  the index to set
     * @param element  the object to set at the specified index
     * @return the object previously at that index
     * @throws UnsupportedOperationException if the underlying list doesn't implement set
     * @throws ClassCastException if the underlying list rejects the element
     * @throws IllegalArgumentException if the underlying list rejects the element
     */
    @Override
    public E set(final int index, final E element) {
        final int size = decorated().size();
        if (index >= size) {
            decorated().addAll(Collections.<E>nCopies(index - size + 1, null));
        }
        return decorated().set(index, element);
    }

}