Question

I have a List, and I want to loop through that List and remove some record base on some condition. Here is what I do

public void foo(List<Bar> recordList){
     for(Bar bar : recordList){
         if(bar.someCondition()){
              recordList.remove(bar);
         }
     }
}

This code generate exception. If I use Iterator then it works fine

public void foo(List<Bar> recordList){
     Iterator<Bar> iter = recordList.iterator();
     while(iter.hasNext()){
         Bar bar = iter.next();
         if(bar.someCondition()){
              iter.remove();
         }
     }
}

I guess my question:

1. Why the first piece of code does not work?

2. How do I make the first piece of code work?

Answer 1

1. It doesn’t work because you are modifying a collection WHILE iterating on it. It means you are changing its state and reading it at the same time. This provokes unexpected behaviours in the inners of the collection, and to prevent data corruption, an exception is thrown.

2. You don’t make it work. You have to use iterators.