Java知識點總結（Java容器-Iterator）

Java知識點總結（Java容器-Iterator）

@(Java知識點總結)[Java, Java容器]

Iterator

Iterator對象稱做迭代器，用於方便地實現對容器內元素的遍歷操做
Iterator接口定義以下：

• boolean hasNext(); //判斷是否有元素沒有被遍歷
• 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
• void remove(); //刪除遊標左面的元素，在執行完next以後該操做只能執行一次

迭代器的使用

HashSet set = new HashSet();
set.add("1" );
set.add("2" );
set.add("3" );
/*Iterator it = set.iterator();
while (it.hasNext()) {
  String  obj = (String) it.next();
  System.out.println(obj);
}*/
for (Iterator it = set.iterator(); it.hasNext();) {
  String  obj  = (String) it.next();
  System.out.println(obj);      
}

Iterator實現

/**
 * Iterator實現原理
 */
private  class Itr implements Iterator<E> {
        int cursor = 0;  //遊標
        int lastRet = -1; //上一次遍歷元素的下標
 
public  boolean hasNext() {
            return cursor != size();
        }
        public E next() {
            checkForComodification();
            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();
            }
        }
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