How to efficiently (performance) remove many items from List in Java?

Question

I have quite large List named items (>= 1,000,000 items) and some condition denoted by that selects items to be deleted and is true for many (maybe hal

Answer 1

I'm sorry, but all these answers are missing the point, I think: You probably don't have to, and probably shouldn't, use a List.

If this kind of "query" is common, why not build an ordered data structure that eliminates the need to traverse all the data nodes? You don't tell us enough about the problem, but given the example you provide a simple tree could do the trick. There's an insertion overhead per item, but you can very quickly find the subtree containing nodes that match , and you therefore avoid most of the comparisons you're doing now.

Furthermore:

• Depending on the exact problem, and the exact data structure you set up, you can speed up deletion -- if the nodes you want to kill do reduce to a subtree or something of the sort, you just drop that subtree, rather than updating a whole slew of list nodes.

• Each time you remove a list item, you are updating pointers -- eg lastNode.next and nextNode.prev or something -- but if it turns out you also want to remove the nextNode, then the pointer update you just caused is thrown away by a new update.)