performance - Deleting objects from an ArrayList in Java

Question

I need to delete some objects from an ArrayList if they meet a condition and I'm wondering which way could be more efficient.

Here's the situation: I have a class that contains an ArrayList containing some other objects. I have to iterate over this ArrayList and delete all elements meeting a certain condition. As far as I know, those would be my options to delete:

1. Create a new ArrayList and add the elements that doesn't meet the condition. After the iteration, swap from the old arraylist to the new one without the elements.

2. Create a new ArrayList and add the elements that meet the condition. After the iteration, use the removeAll() method passing the ArrayList with the objects to be deleted.

Is there a more efficient way to delete objects from an ArrayList?

Answer 1

You could iterate backwards and remove as you go through the ArrayList. This has the advantage of subsequent elements not needing to shift and is easier to program than moving forwards.