java Iterator接口和LIstIterator接口分析

/** * An iterator over a collection. {@code Iterator} takes the place of * {@link Enumeration} in the Java Collections Framework. Iterators * differ from enumerations in two ways: * Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. * Method names have been improved. * This interface is a member of the Java Collections Framework. * @param <E> the type of elements returned by this iterator*/public interface Iterator<E> {  /**   * Returns {@code true} if the iteration has more elements.   * (In other words, returns {@code true} if {@link #next} would   * return an element rather than throwing an exception.)   * @return {@code true} if the iteration has more elements   */  boolean hasNext();  /**   * Returns the next element in the iteration.   * @return the next element in the iteration   * @throws NoSuchElementException if the iteration has no more elements   */  E next();  /**   * Removes from the underlying collection the last element returned   * by this iterator (optional operation). This method can be called   * only once per call to {@link #next}. The behavior of an iterator   * is unspecified if the underlying collection is modified while the   * iteration is in progress in any way other than by calling this   * method.   *   * @implSpec   * The default implementation throws an instance of   * {@link UnsupportedOperationException} and performs no other action.   *   * @throws UnsupportedOperationException if the {@code remove}   *     operation is not supported by this iterator   *   * @throws IllegalStateException if the {@code next} method has not   *     yet been called, or the {@code remove} method has already   *     been called after the last call to the {@code next}   *     method   */  default void remove() {    throw new UnsupportedOperationException("remove");  }  /**   * Performs the given action for each remaining element until all elements   * have been processed or the action throws an exception. Actions are   * performed in the order of iteration, if that order is specified.   * Exceptions thrown by the action are relayed to the caller.   *   * @implSpec   * <p>The default implementation behaves as if:   * <pre>{@code   *   while (hasNext())   *     action.accept(next());   * }</pre>   *   * @param action The action to be performed for each element   * @throws NullPointerException if the specified action is null   * @since 1.8   */  default void forEachRemaining(Consumer<? super E> action) {    Objects.requireNonNull(action);    while (hasNext())      action.accept(next());  }}

/** * 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()}. * * This interface is a member of the Java Collections Framework.*/public interface ListIterator<E> extends Iterator<E> {  // Query Operations  /**   * 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   */  boolean hasNext();  /**   * 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   */  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   */  boolean hasPrevious();  /**   * 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   */  E previous();  /**   * 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   */  int nextIndex();  /**   * 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   */  int previousIndex();  // Modification Operations  /**   * 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}   */  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}   */  void set(E e);  /**   * 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   */  void add(E e);}