public static void main(String[] args) {
  List<Integer> list = new ArrayList<Integer>();
  list.add(1);
  list.add(2);
  list.add(2);
  list.add(3);
  list.add(4);
  
  for (int i = 0; i < list.size(); i++) {
   if(2 == list.get(i)){
    list.remove(i);
   }
   System.out.println(list.get(i));
  }
  
  System.out.println("list=" + list.toString());
  
 }

1
2
3
4
list=[1, 2, 3, 4]

public static void listIterator2(){
  List<Integer> list = new ArrayList<Integer>();
  list.add(1);
  list.add(2);
  list.add(2);
  list.add(3);
  list.add(4);
  
  for (int value : list) {
   if(2 == value){
    list.remove(value);
   }
   System.out.println(value);
  }
  
  System.out.println("list=" + list.toString());
  
 }

Exception in thread "main" 1
2
java.util.ConcurrentModificationException
 at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
 at java.util.ArrayList$Itr.next(Unknown Source)
 at test.ListIterator.listIterator2(ListIterator.java:39)
 at test.ListIterator.main(ListIterator.java:10)

public static void listIterator3(){
  List<Integer> list = new ArrayList<Integer>();
  list.add(1);
  list.add(2);
  list.add(2);
  list.add(3);
  list.add(4);
  
  Iterator<Integer> it = list.iterator();
  while (it.hasNext()){
   Integer value = it.next();
   if (2 == value) {
    it.remove();
   }
   
   System.out.println(value);
  }
  
  System.out.println("list=" + list.toString());
 }

1
2
2
3
4
list=[1, 3, 4]

public static void main(String[] args) {
 HashMap<String, String> map = new HashMap<String, String>();
 map.put("1", "test1");
 map.put("2", "test2");
 map.put("3", "test3");
 map.put("4", "test4");
 
 //完整遍历Map
 for (Entry<String, String> entry : map.entrySet()) {
  System.out.printf("key: %s value:%s\r\n", entry.getKey(), entry.getValue());
 }
 
 //删除元素
 Iterator<Map.Entry<String, String>> it = map.entrySet().iterator(); 
 while(it.hasNext())
 { 
  Map.Entry<String, String> entry= it.next(); 
  String key= entry.getKey(); 
  int k = Integer.parseInt(key);
  if(k%2==1)
  { 
   System.out.printf("delete key:%s value:%s\r\n", key, entry.getValue());
   it.remove(); 
  } 
 } 
 
 //完整遍历Map
 for (Entry<String, String> entry : map.entrySet()) {
  System.out.printf("key: %s value:%s\r\n", entry.getKey(), entry.getValue());
 }
}

key: 1 value:test1
key: 2 value:test2
key: 3 value:test3
key: 4 value:test4
delete key:1 value:test1
delete key:3 value:test3
key: 2 value:test2
key: 4 value:test4