114_容器_迭代器遍歷List和Set_List迭代器源代碼分析

Iterator接口：

• 所有實現了Collection接口的容器類都有一個iterator方法用以返回一個實現Iterator接口的對象

• Iterator對象稱作爲迭代器，以方便的對容器內元素的遍歷操作

• Iterator接口定義瞭如下方法：

    1. boolean hashNext(); //判斷是否有元素沒有被遍歷
    2. Object next(); //返回遊標當前位置的元素並將遊標移動到下一個位置
    3.  void remove(); //刪除遊標左邊的元素，在執行完next之後該操作只能執行一次。

public class Test{
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");

        //通過索引遍歷List
        for(int i=0;i<list.size();i++){
            System.out.println(list.get(i));
        }
        //通過迭代器遍歷List
        for(Iterator iter1 = list.iterator();iter1.hasNext();){
            String str = (String) iter1.next();
            System.out.println(str);
            iter1.remove();
            //iter1.remove();
        }

        System.out.println(list.size()+"******");

        Set set = new HashSet();
        set.add("高1");
        set.add("高2");
        set.add("高3");

        //通過迭代器遍歷Set
//      Iterator iter = set.iterator();
//      while(iter.hasNext()){
        for(Iterator iter = set.iterator();iter.hasNext();){
            String str = (String) iter.next();
            System.out.println(str);
        }   
    }
}

list迭代器的源碼分析

private class Itr implements Iterator<E> {
        int cursor = 0;

        int lastRet = -1;

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

        public E next() {
            try {
                int i = cursor;
                E next = get(i);
                lastRet = i;
                cursor = i + 1;
                return next;
            } catch (IndexOutOfBoundsException e) {
                checkForComodification();
                throw new NoSuchElementException();
            }
        }

        public void remove() {
            if (lastRet < 0)
                throw new IllegalStateException();
            checkForComodification();
            try {
                AbstractList.this.remove(lastRet);
                if (lastRet < cursor)
                    cursor--;
                lastRet = -1;
                expectedModCount = modCount;
            } catch (IndexOutOfBoundsException e) {
                throw new ConcurrentModificationException();
            }
        }