Iterator.java

/* Iterator.java -- Interface for iterating over collections
   Copyright (C) 1998, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.util;

/**
 * An object which iterates over a collection. An Iterator is used to return
 * the items once only, in sequence, by successive calls to the next method.
 * It is also possible to remove elements from the underlying collection by
 * using the optional remove method. Iterator is intended as a replacement
 * for the Enumeration interface of previous versions of Java, which did not
 * have the remove method and had less conveniently named methods.
 *
 * @author Original author unknown
 * @author Eric Blake <ebb9@email.byu.edu>
 * @see Collection
 * @see ListIterator
 * @see Enumeration
 * @since 1.2
 * @status updated to 1.4
 */
public interface Iterator
{
  /**
   * Tests whether there are elements remaining in the collection. In other
   * words, calling <code>next()</code> will not throw an exception.
   *
   * @return true if there is at least one more element in the collection
   */
  boolean hasNext();

  /**
   * Obtain the next element in the collection.
   *
   * @return the next element in the collection
   * @throws NoSuchElementException if there are no more elements
   */
  Object next();

  /**
   * Remove from the underlying collection the last element returned by next
   * (optional operation). This method can be called only once after each
   * call to <code>next()</code>. It does not affect what will be returned
   * by subsequent calls to next.
   *
   * @throws IllegalStateException if next has not yet been called or remove
   *         has already been called since the last call to next.
   * @throws UnsupportedOperationException if this Iterator does not support
   *         the remove operation.
   */
  void remove();
}