List<String> list =new ArrayList<String>();
        list.add("boss");
        list.add("good");
        list.add("No");
        list.add("Fine");
        System.out.println(list);//[boss, good, No, Fine]
        Collections.sort(list);
        System.out.println(list);//[Fine, No, boss, good]
        list.add("我们");
        list.add("你就是");
        list.add("他很调");
        list.add("明天见");
        int i=0;
        while(true){
        
        for (String dwonCountCmd : list) {
            
                if (i<30) {
                    System.out.println(dwonCountCmd+i);
                    i++;
                } else{
//在循环中把集合的一个元素移除了，如果此时不break的话，就会报错
                    list.remove(dwonCountCmd);
                    System.out.println(list.toString());
                    break;
                }
            }
        }
        

 

 

会报这种错

Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
    at java.util.AbstractList$Itr.next(Unknown Source)
    at Test2.main(Test2.java:47)