Method to delete specific elements in java collection class arraylist loop

During project development, we may often need to dynamically delete some elements in the ArrayList.

A wrong way:

<pre name="code" class="java">for(int i = 0 , len= list.size();i<len;++i){
  
 if(list.get(i)==XXX){
  
    list.remove(i);
  
 }
  
}

The above method will throw the following exception:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
  at java.util.ArrayList.RangeCheck(Unknown Source)
  at java.util.ArrayList.get(Unknown Source)
  at ListDemo.main(ListDemo.java:20)

Because you deleted the element, but did not change the iteration subscript, so when the iteration reaches the last one An exception will be thrown.

The above program can be improved as follows:

for(int i = 0 , len= list.size();i<len;++i){
  
 if(list.get(i)==XXX){
  
    list.remove(i);
    --len;//减少一个
 }
  
}

The above code is correct.

Let’s introduce another solution below:

The List interface implements the Iterator interface internally, providing developers with an iterator() to get an iterator object of the current list object.

Iterator<String> sListIterator = list.iterator();
while(sListIterator.hasNext()){
  String e = sListIterator.next();
  if(e.equals("3")){
  sListIterator.remove();
  }
}

The above is also correct, and the second option is recommended.

The implementation principles of the two solutions are quite different. The second one is just encapsulated by jdk.

Looking at the ArrayList source code, you will find that many methods are internally implemented based on the iterator interface, so it is recommended to use the second solution.

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