ListIterator.java

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package java.util;

/**
 * An iterator for lists that allows the programmer
 * to traverse the list in either direction, modify
 * the list during iteration, and obtain the iterator's
 * current position in the list. A {@code ListIterator}
 * has no current element; its <I>cursor position</I> always
 * lies between the element that would be returned by a call
 * to {@code previous()} and the element that would be
 * returned by a call to {@code next()}.
 * An iterator for a list of length {@code n} has {@code n+1} possible
 * cursor positions, as illustrated by the carets ({@code ^}) below:
 * <PRE>
 * Element(0)   Element(1)   Element(2)   ... Element(n-1)
 * cursor positions:  ^            ^            ^            ^                  ^
 * </PRE>
 * Note that the {@link #remove} and {@link #set(Object)} methods are
 * <i>not</i> defined in terms of the cursor position;  they are defined to
 * operate on the last element returned by a call to {@link #next} or
 * {@link #previous()}.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @author Josh Bloch
 * @see Collection
 * @see List
 * @see Iterator
 * @see Enumeration
 * @see List#listIterator()
 * @since 1.2
 */
// 增强的线性表迭代器，支持向前/向后遍历元素
public interface ListIterator<E> extends Iterator<E> {
    
    /**
     * Returns {@code true} if this list iterator has more elements when
     * traversing the list in the forward direction. (In other words,
     * returns {@code true} if {@link #next} would return an element rather
     * than throwing an exception.)
     *
     * @return {@code true} if the list iterator has more elements when
     * traversing the list in the forward direction
     */
    // 是否存在下一个元素
    boolean hasNext();
    
    /**
     * Returns the index of the element that would be returned by a
     * subsequent call to {@link #next}. (Returns list size if the list
     * iterator is at the end of the list.)
     *
     * @return the index of the element that would be returned by a
     * subsequent call to {@code next}, or list size if the list
     * iterator is at the end of the list
     */
    // 下一个元素的索引
    int nextIndex();
    
    /**
     * Returns the next element in the list and advances the cursor position.
     * This method may be called repeatedly to iterate through the list,
     * or intermixed with calls to {@link #previous} to go back and forth.
     * (Note that alternating calls to {@code next} and {@code previous}
     * will return the same element repeatedly.)
     *
     * @return the next element in the list
     *
     * @throws NoSuchElementException if the iteration has no next element
     */
    // 返回下一个元素
    E next();
    
    /**
     * Returns {@code true} if this list iterator has more elements when
     * traversing the list in the reverse direction.  (In other words,
     * returns {@code true} if {@link #previous} would return an element
     * rather than throwing an exception.)
     *
     * @return {@code true} if the list iterator has more elements when
     * traversing the list in the reverse direction
     */
    // 是否存在上一个元素
    boolean hasPrevious();
    
    /**
     * Returns the index of the element that would be returned by a
     * subsequent call to {@link #previous}. (Returns -1 if the list
     * iterator is at the beginning of the list.)
     *
     * @return the index of the element that would be returned by a
     * subsequent call to {@code previous}, or -1 if the list
     * iterator is at the beginning of the list
     */
    // 上一个元素的索引
    int previousIndex();
    
    /**
     * Returns the previous element in the list and moves the cursor
     * position backwards.  This method may be called repeatedly to
     * iterate through the list backwards, or intermixed with calls to
     * {@link #next} to go back and forth.  (Note that alternating calls
     * to {@code next} and {@code previous} will return the same
     * element repeatedly.)
     *
     * @return the previous element in the list
     *
     * @throws NoSuchElementException if the iteration has no previous
     *                                element
     */
    // 返回上一个元素
    E previous();
    
    /**
     * Inserts the specified element into the list (optional operation).
     * The element is inserted immediately before the element that
     * would be returned by {@link #next}, if any, and after the element
     * that would be returned by {@link #previous}, if any.  (If the
     * list contains no elements, the new element becomes the sole element
     * on the list.)  The new element is inserted before the implicit
     * cursor: a subsequent call to {@code next} would be unaffected, and a
     * subsequent call to {@code previous} would return the new element.
     * (This call increases by one the value that would be returned by a
     * call to {@code nextIndex} or {@code previousIndex}.)
     *
     * @param e the element to insert
     *
     * @throws UnsupportedOperationException if the {@code add} method is
     *                                       not supported by this list iterator
     * @throws ClassCastException            if the class of the specified element
     *                                       prevents it from being added to this list
     * @throws IllegalArgumentException      if some aspect of this element
     *                                       prevents it from being added to this list
     */
    // 将指定的元素添加到下一个待遍历的位置
    void add(E e);
    
    /**
     * Removes from the list the last element that was returned by {@link
     * #next} or {@link #previous} (optional operation).  This call can
     * only be made once per call to {@code next} or {@code previous}.
     * It can be made only if {@link #add} has not been
     * called after the last call to {@code next} or {@code previous}.
     *
     * @throws UnsupportedOperationException if the {@code remove}
     *                                       operation is not supported by this list iterator
     * @throws IllegalStateException         if neither {@code next} nor
     *                                       {@code previous} have been called, or {@code remove} or
     *                                       {@code add} have been called after the last call to
     *                                       {@code next} or {@code previous}
     */
    // 移除上一个遍历的元素
    void remove();
    
    /**
     * Replaces the last element returned by {@link #next} or
     * {@link #previous} with the specified element (optional operation).
     * This call can be made only if neither {@link #remove} nor {@link
     * #add} have been called after the last call to {@code next} or
     * {@code previous}.
     *
     * @param e the element with which to replace the last element returned by
     *          {@code next} or {@code previous}
     *
     * @throws UnsupportedOperationException if the {@code set} operation
     *                                       is not supported by this list iterator
     * @throws ClassCastException            if the class of the specified element
     *                                       prevents it from being added to this list
     * @throws IllegalArgumentException      if some aspect of the specified
     *                                       element prevents it from being added to this list
     * @throws IllegalStateException         if neither {@code next} nor
     *                                       {@code previous} have been called, or {@code remove} or
     *                                       {@code add} have been called after the last call to
     *                                       {@code next} or {@code previous}
     */
    // 将上一个遍历过的元素更新为e
    void set(E e);
    
}