AbstractSequentialList.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.util;

/**
 * This class provides a skeletal implementation of the {@code List}
 * interface to minimize the effort required to implement this interface
 * backed by a "sequential access" data store (such as a linked list).  For
 * random access data (such as an array), {@code AbstractList} should be used
 * in preference to this class.<p>
 *
 * This class is the opposite of the {@code AbstractList} class in the sense
 * that it implements the "random access" methods ({@code get(int index)},
 * {@code set(int index, E element)}, {@code add(int index, E element)} and
 * {@code remove(int index)}) on top of the list's list iterator, instead of
 * the other way around.<p>
 *
 * To implement a list the programmer needs only to extend this class and
 * provide implementations for the {@code listIterator} and {@code size}
 * methods.  For an unmodifiable list, the programmer need only implement the
 * list iterator's {@code hasNext}, {@code next}, {@code hasPrevious},
 * {@code previous} and {@code index} methods.<p>
 *
 * For a modifiable list the programmer should additionally implement the list
 * iterator's {@code set} method.  For a variable-size list the programmer
 * should additionally implement the list iterator's {@code remove} and
 * {@code add} methods.<p>
 *
 * The programmer should generally provide a void (no argument) and collection
 * constructor, as per the recommendation in the {@code Collection} interface
 * specification.<p>
 *
 * This class is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Collection
 * @see List
 * @see AbstractList
 * @see AbstractCollection
 * @since 1.2
 */
// 对抽象线性表的进一步实现
public abstract class AbstractSequentialList<E> extends AbstractList<E> {
    
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractSequentialList() {
    }
    
    /**
     * Inserts the specified element at the specified position in this list
     * (optional operation).  Shifts the element currently at that position
     * (if any) and any subsequent elements to the right (adds one to their
     * indices).
     *
     * <p>This implementation first gets a list iterator pointing to the
     * indexed element (with {@code listIterator(index)}).  Then, it
     * inserts the specified element with {@code ListIterator.add}.
     *
     * <p>Note that this implementation will throw an
     * {@code UnsupportedOperationException} if the list iterator does not
     * implement the {@code add} operation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     * @throws IndexOutOfBoundsException     {@inheritDoc}
     */
    // 将元素element添加到线性表index处
    public void add(int index, E element) {
        try {
            listIterator(index).add(element);
        } catch(NoSuchElementException exc) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
    }
    
    /**
     * Inserts all of the elements in the specified collection into this
     * list at the specified position (optional operation).  Shifts the
     * element currently at that position (if any) and any subsequent
     * elements to the right (increases their indices).  The new elements
     * will appear in this list in the order that they are returned by the
     * specified collection's iterator.  The behavior of this operation is
     * undefined if the specified collection is modified while the
     * operation is in progress.  (Note that this will occur if the specified
     * collection is this list, and it's nonempty.)
     *
     * <p>This implementation gets an iterator over the specified collection and
     * a list iterator over this list pointing to the indexed element (with
     * {@code listIterator(index)}).  Then, it iterates over the specified
     * collection, inserting the elements obtained from the iterator into this
     * list, one at a time, using {@code ListIterator.add} followed by
     * {@code ListIterator.next} (to skip over the added element).
     *
     * <p>Note that this implementation will throw an
     * {@code UnsupportedOperationException} if the list iterator returned by
     * the {@code listIterator} method does not implement the {@code add}
     * operation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     * @throws IndexOutOfBoundsException     {@inheritDoc}
     */
    // 将指定容器中的元素添加到当前线性表的index处
    public boolean addAll(int index, Collection<? extends E> c) {
        try {
            boolean modified = false;
            ListIterator<E> e1 = listIterator(index);
            for(E e : c) {
                e1.add(e);
                modified = true;
            }
            return modified;
        } catch(NoSuchElementException exc) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
    }
    
    /**
     * Returns the element at the specified position in this list.
     *
     * <p>This implementation first gets a list iterator pointing to the
     * indexed element (with {@code listIterator(index)}).  Then, it gets
     * the element using {@code ListIterator.next} and returns it.
     *
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    // 获取指定索引处的元素
    public E get(int index) {
        try {
            return listIterator(index).next();
        } catch(NoSuchElementException exc) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
    }
    
    /**
     * Removes the element at the specified position in this list (optional
     * operation).  Shifts any subsequent elements to the left (subtracts one
     * from their indices).  Returns the element that was removed from the
     * list.
     *
     * <p>This implementation first gets a list iterator pointing to the
     * indexed element (with {@code listIterator(index)}).  Then, it removes
     * the element with {@code ListIterator.remove}.
     *
     * <p>Note that this implementation will throw an
     * {@code UnsupportedOperationException} if the list iterator does not
     * implement the {@code remove} operation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws IndexOutOfBoundsException     {@inheritDoc}
     */
    // 移除索引index处的元素，返回被移除的元素
    public E remove(int index) {
        try {
            ListIterator<E> e = listIterator(index);
            E outCast = e.next();
            e.remove();
            return outCast;
        } catch(NoSuchElementException exc) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
    }
    
    /**
     * Replaces the element at the specified position in this list with the
     * specified element (optional operation).
     *
     * <p>This implementation first gets a list iterator pointing to the
     * indexed element (with {@code listIterator(index)}).  Then, it gets
     * the current element using {@code ListIterator.next} and replaces it
     * with {@code ListIterator.set}.
     *
     * <p>Note that this implementation will throw an
     * {@code UnsupportedOperationException} if the list iterator does not
     * implement the {@code set} operation.
     *
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     * @throws IndexOutOfBoundsException     {@inheritDoc}
     */
    // 将index处的元素更新为element，并返回旧元素
    public E set(int index, E element) {
        try {
            ListIterator<E> e = listIterator(index);
            E oldVal = e.next();
            e.set(element);
            return oldVal;
        } catch(NoSuchElementException exc) {
            throw new IndexOutOfBoundsException("Index: " + index);
        }
    }
    
    /**
     * Returns an iterator over the elements in this list (in proper
     * sequence).<p>
     *
     * This implementation merely returns a list iterator over the list.
     *
     * @return an iterator over the elements in this list (in proper sequence)
     */
    // 返回当前线性表的一个迭代器
    public Iterator<E> iterator() {
        return listIterator();
    }
    
    /**
     * Returns a list iterator over the elements in this list (in proper
     * sequence).
     *
     * @param index index of first element to be returned from the list
     *              iterator (by a call to the {@code next} method)
     *
     * @return a list iterator over the elements in this list (in proper
     * sequence)
     *
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    // 返回当前线性表的一个增强的迭代器，且设定下一个待遍历元素为索引index处的元素
    public abstract ListIterator<E> listIterator(int index);
    
}