Summary of methods for looping to delete elements in a list in java

In my impression, there is a problem with using a for loop to cyclically delete elements in a list, but you can use an enhanced for loop. Then I found an error when using it today, and then I went to do some science research, and then I found out that this was a misunderstanding. Let’s talk about it below. . If you reach out, you can jump directly to the end of the article. See summary. .

There are three ways to loop through a list in JAVA: for loop, enhanced for loop (also known as foreach loop), and iterator traversal.

1. The for loop traverses the list

for(int i=0;i<list.size();i++){
  if(list.get(i).equals("del"))
    list.remove(i);
}

The problem with this method is that after deleting an element, the size of the list changes, and your index also changes, so it will cause you to miss something when traversing. Remove certain elements. For example, when you delete the first element and continue to access the second element according to the index, because the subsequent elements are moved forward by one position due to the deletion, the third element is actually accessed. Therefore, this method can be used when deleting a specific element, but it is not suitable for deleting multiple elements in a loop.

2. Enhanced for loop

for(String x:list){
  if(x.equals("del"))
    list.remove(x);
}

The problem with this method is that continuing to loop after deleting the element will report the error message ConcurrentModificationException, because the element is modified concurrently when used, causing an exception to be thrown. However, if you use break to jump out immediately after deletion, no error will be triggered.

3. Iterator traversal

Iterator<String> it = list.iterator();
while(it.hasNext()){
  String x = it.next();
  if(x.equals("del")){
    it.remove();
  }
}

This method can cycle and delete normally. But it should be noted that if you use the remove method of iterator, if you use the remove method of list, you will also report the ConcurrentModificationException error mentioned above.

Summary:

(1) To loop through a specific element in the list, you can use any of the three methods, but you should pay attention to the issues analyzed above during use.

(2) To loop through multiple elements in a list, you should use the iterator method.

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