Practice with CollectionsJava
Let's pause before moving on to get more practice with Java's collections—the lists, maps, and sets that are so useful for solving problems. We'll also learn how we can combine these collections together to build more interesting data structures. Let's get started!
Nested Collections
In the past lessons we've seen how to create and use several standard Java collections: Lists, Maps, and Sets:
These collections are quite useful on their own! However, they can also be combined to great effect. Let's see an example.
Lists of Maps of Sets
You can combine Lists, Maps, and Sets in many interesting ways to build data structures to solve problems.
You can create Lists of Maps:
Or Sets of Lists:
But generally, it's more common for the top-level data structure to be a Map: Maps of Maps, Maps of Lists, and Maps of Sets.
We'll get some practice working with these on this lesson's practice and homework problems.
Practice Problem Warm-Up
We'll spend the rest of the lesson working on some problems that test our understanding of how to nest collections.
First, we're asked to parse a List<String> into a Map<Set<String>>.
Let's do an example of that together, which you can use as a starting point for the practice problem that follows.
Homework Warm-Up
Next let's discuss how to approach this lesson's homework problem.
This problem is a bit trickier, since we need to determine when to properly insert entries into our Map, and do some String parsing.
So let's discuss how to get started.
More Practice
Need more practice? Head over to the practice page.