Every example I find is about doing this alphabetically, while I need my elements sorted by date. My ArrayList contains objects on which one of the datamembers is a DateTime object. On DateTime I ...

Have a look at the Comparator and Collections classes. A simple way would be to implement the Comparable interface in AgentSummaryDTO and then pass the list to Collections.sort().

Unmodifiable collections are usually read-only views (wrappers) of other collections. You can't add to, remove from or clear them, but the underlying collection can change. Immutable collections can't be …

Again, to use Collections.sort, you need one of these to be true: The type must be Comparable (use the 1-arg sort) A Comparator for the type must be provided (use the 2-args sort) When to use …

Eclipse Collections If you're using pairs that contain primitives, Eclipse Collections provides some very efficient primitive pair classes that will avoid all the inefficient auto-boxing and auto-unboxing.

The other advantage of using Apache commons-collections CollectionUtils.isEmpty (or CollectionUtils.isNotEmpty) is that your if condition has less branches, so it is easier to reach a good …

I have a list of "Report" objects with three fields (All String type)- ReportKey StudentNumber School I have a sort code goes like- Collections.sort(reportList, new Comparator<Report>() { @

Today I was happily coding away when I got to a piece of code I already used hundreds of times: Iterating through a Collection (here ArrayList) For some reason, I actually looked at the autocompl...

java collections - keyset () vs entrySet () in map Asked 13 years, 10 months ago Modified 6 years, 10 months ago Viewed 122k times

But this is not the java.util.ArrayList. It's very similar though. Note that this constructor takes the array and places it as the backing array of the list. So it is O(1). In case you already have the list created, …