The difference between arrayslist and LinkedList

1、 Whether threads are safe

        because ArrayList and LinkedLit It's all out of sync , That is, thread safety is not guaranteed

2、 Underlying data structure

        ArrayList The underlying data structure of is Object Array to achieve ;LinkedList It is achieved by using linked lists （JDK1.6 It used to be a circular list ,JDK1.7 Then the cycle is cancelled ）.

3、 Whether the deletion or insertion of data is affected by the location

        ArrayList Because it is implemented by array , So when the position of insertion or deletion is not at the end of the array , Then his time complexity is O(1), When the position is i In position , Because when deleting, you need to move the following elements forward , When inserting , Just move the following elements back , So time complexity is O(n-i); and LinkedList The bottom layer of is implemented by using linked lists , When inserting or deleting elements at the beginning and end , Time complexity O(1), When it is necessary to insert the specified position , You need to move to the specified position first , Inserting or deleting , So the time complexity is O(n).

4、 Can I have random access

        ArrayList It's an array implementation , So you can randomly access , Query through its array index ,LinkedList Random query is not supported

 5、 Occupancy space

        ArrayList Use arrays to implement , Finally, a space will be left , So it takes up more space ; and LinkedList Use the list , Will not appear in the back to leave room , But when storing each element , It will also store the front drive and rear drive keys , So it will be better than ArrayList Take up more space