public Iterator<E> iterator() {return new Itr();
}private class Itr implements Iterator<E> {int cursor;       // index of next element to returnint lastRet = -1; // index of last element returned; -1 if no suchpublic boolean hasNext() {return cursor != size;}@SuppressWarnings("unchecked")public E next() {int i = cursor;Object[] elementData = ArrayList.this.elementData;cursor = i + 1;return (E) elementData[lastRet = i];}public void remove() {ArrayList.this.remove(lastRet);cursor = lastRet;lastRet = -1;expectedModCount = modCount;}
}
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;}@SuppressWarnings("unchecked")public E previous() {int i = cursor - 1;Object[] elementData = ArrayList.this.elementData;cursor = i;return (E) elementData[lastRet = i];}public void set(E e) {}public void add(E e) {}
}

import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class TestListItr {  public static void main(String[] args) {ArrayList<String> list = new ArrayList<String>();for (int i = 0; i < 5; i++) {list.add("a" + i);}System.out.println(list);for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {String temp = iterator.next();System.out.print(temp + "t");if(temp.endsWith("3")) {iterator.remove();}}System.out.println();System.out.println(list);
//      for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {
//          String temp = iterator.next();
//          System.out.print(temp + "t");
//          if(temp.endsWith("4")) {
//              list.add("a5");//运行时异常ConcurrentModificationException并发修改异常
//          }
//      }//ListIterator是Iterator接口的扩展，用于解决并发修改异常 for (ListIterator<String> iterator = list.listIterator(); iterator.hasNext();) {String temp = iterator.next();System.out.print(temp + "t");if(temp.endsWith("4")) {iterator.add("a5");}}System.out.println();System.out.println(list);}
}

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;
public class TestMapItr {   public static void main(String[] args) {HashMap<String,Integer> map = new HashMap<String, Integer>();map.put("hello", 123);map.put("world", 456);map.put("java", 789);//方式一Set<String> keySet = map.keySet();for (Iterator<String> iterator = keySet.iterator(); iterator.hasNext();) {String key = iterator.next();System.out.print(key + "=" + map.get(key) + "t");}System.out.println();//方式二  Entry<String, Integer>键值关系的类型Set<Entry<String, Integer>> entrySet = map.entrySet();for (Iterator<Entry<String, Integer>> iterator = entrySet.iterator(); iterator.hasNext();) {Entry<String, Integer> entry = iterator.next();System.out.print(entry.getKey() + "--" + entry.getValue() + "t");}System.out.println();}
}