Iterator is deeply built into Java already, so the real lesson is not “what is an iterator?” but “when should you build custom traversal and how should it behave?”
Iterator matters when:
- traversal should not expose internal representation
- traversal order is a design choice
- multiple traversal styles may exist
- clients need a stable cursor-like API
The pattern is strong in custom collections, trees, graphs, and domain-specific aggregates. It is weak when a standard collection already expresses the data cleanly.
In this section
- Implementing Iterator in Java
Implement Java iterators when custom aggregates need explicit traversal without exposing their internal representation.
- Internal vs. External Iterators
Compare Java external iterators with callback- or stream-style internal iteration so traversal control stays intentional.
- Fail-Fast and Fail-Safe Iterators
Understand Java fail-fast and fail-safe iterator behavior so mutation and traversal expectations stay realistic.
- Enhancing Iterators
Extend Java iterators carefully when traversal needs filtering, peeking, or domain-specific movement without turning the cursor API into a grab bag.
- Iterator Pattern Use Cases and Examples in Java
See where Iterator genuinely helps in Java systems, especially for custom aggregates, trees, graphs, and domain-specific traversal order.