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Clojure collections are immutable and persistent; Java collections are typically mutable. Interop requires moving values between them carefully.

Most Java collections implement Iterable, so Clojure's seq functions work on them directly.

Construct and mutate a Java list using interop method calls.

Wrap a Java collection in vec or into to get an immutable Clojure structure.

A Clojure map is already a java.util.Map, so it can be passed to Java APIs expecting one. For a mutable copy, build a HashMap.

Java APIs often want primitive arrays. Create them with typed constructors like int-array and double-array.

Use aget to read and aset to write array slots by index.

Wrap an array in seq or vec to process it with Clojure's sequence functions.

Add type hints so the compiler avoids reflection on hot array loops.

When you hand a mutable Java collection to other code, both sides see mutations. Copy into an immutable Clojure structure when you need isolation.

Keep mutable Java collections at the interop boundary and convert to immutable Clojure data as early as possible, so the rest of your code stays purely functional.

Test your Java collection interop knowledge.

You learned that Java collections are seqable, how to convert between Java and Clojure collections, build and read primitive arrays, add type hints, and keep mutation at the interop boundary.