Iterator Design Pattern — Java Example
Pattern: Behavioral → Iterator Article: https://ankurm.com/iterator-design-pattern-java/
What this example shows
A BookShelf stores Book objects in an internal ArrayList but never exposes it. Callers only see the BookIterator interface (hasNext()/next()). BookShelf hands out two different concrete iterators: ForwardIterator walks every book in order, and DecadeIterator filters to only books published in a given decade, computing the next match lazily as advance() is called. Main exercises both iterators, then prints a line noting that java.util.Iterator/for-each work the same way under the hood.
How to run
javac iterator/*.java -d out/iterator
java -cp out/iterator iterator.Main
Requires Java 25.
Post Section ↔ File Mapping
| Post Section | File(s) |
|---|---|
| Custom Iterator Implementation — the Iterator interface | BookIterator.java |
| Custom Iterator Implementation — the element type | Book.java |
| Custom Iterator Implementation — the Aggregate (BookShelf, ForwardIterator, DecadeIterator) | BookShelf.java |
| Custom Iterator Implementation — wiring it together | Main.java |
Note: the "How Java's For-Each Loop Uses Iterator" snippet (Iterable<Book> example) is illustrative only — it is not part of this repository's runnable example.
Article: https://ankurm.com/iterator-design-pattern-java/ All patterns: https://ankurm.com/design-patterns-java/