public class Test {
    public static void main(String[] args) {
        Course java = new Course("Java架构");
        Course javaBase = new Course("Java基础");
        Course design = new Course("设计模式");
        Course ai = new Course("人工智能");

        ICourseAggregate aggregate = new CourseAggregateImpl();
        aggregate.add(java);
        aggregate.add(javaBase);
        aggregate.add(design);
        aggregate.add(ai);

        System.out.println("===========课程列表==========");
        printCourse(aggregate);

        aggregate.remove(ai);

        System.out.println("===========删除操作之后的课程列表==========");
        printCourse(aggregate);
    }

    private static void printCourse(ICourseAggregate aggregate) {
        Iterator<Course> i = aggregate.iterator();
        while (i.hasNext()){
            Course course = i.next();
            System.out.println("《" + course.getName()  + "》");
        }
    }
}

public interface Iterator<E> {
    boolean hasNext();

    E next();

    default void remove() {
        throw new UnsupportedOperationException("remove");
    }

    default void forEachRemaining(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        while (hasNext())
            action.accept(next());
    }
}

public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    private class Itr implements Iterator<E> {
        int cursor;       // index of next element to return
        int lastRet = -1; // index of last element returned; -1 if no such
        int expectedModCount = modCount;

        public boolean hasNext() {
            return cursor != size;
        }

        @SuppressWarnings("unchecked")
        public E next() {
            checkForComodification();
            int i = cursor;
            if (i >= size)
                throw new NoSuchElementException();
            Object[] elementData = ArrayList.this.elementData;
            if (i >= elementData.length)
                throw new ConcurrentModificationException();
            cursor = i + 1;
            return (E) elementData[lastRet = i];
        }

        ...
    }
}

private class ListItr extends Itr implements ListIterator<E> {
    ListItr(int index) {
        super();
        cursor = index;
    }

    public boolean hasPrevious() {
        return cursor != 0;
    }

    public int nextIndex() {
        return cursor;
    }

    public int previousIndex() {
        return cursor - 1;
    }

    ...
}

它增加了 hasPreviousQ方法是否还有上一个等这样的判断。另外还有SubList对子集合的迭代处理。

当然,迭代器模式在MyBatis中也是必不可少的，来看一个Defaultcursor类 ：

public class DefaultCursor<T> implements Cursor<T> {
    ...
    private final CursorIterator cursorIterator = new CursorIterator();
}