Debugging: Filtering Arrays and Collections in IntelliJ IDEA

As usual, the newest version of IntelliJ IDEA contains updates to help you debug applications. Given that we are working more and more with large data sets, IntelliJ IDEA 2017.2 has added the ability to filter arrays and collections in our variables or watches.

In this example, I have a variable, allWords, that’s a list of Strings. This is a large list, so when I’m debugging my application, I may want to look for specific values, or types of values, in this list. I can do this by right-clicking on the list and selecting “filter”.

Then I can enter the criteria to filter. As you’d expect, IntelliJ IDEA offers code completion and suggestions here.

The debug window will now show me the subset of values in the list that match these criteria.

If I right-click on the filter, I can edit the filter to change the original criteria or add further filters:

And I can easily remove the filter using the clear button:

This feature also works on other Collection types and arrays. Here, we’ve added a watch expression that creates an array of random ints:

We can filter these values, too:

This ability to filter the values in large collections like lists and arrays make it easier for us, as we’re debugging an application, to see which values are available, and particularly if one or more of them match some criteria we’re looking for.