32 lines
1.5 KiB
Markdown
32 lines
1.5 KiB
Markdown
# Iterator Design Pattern — Java Example
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**Pattern:** Behavioral → Iterator
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**Article:** https://ankurm.com/iterator-design-pattern-java/
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## What this example shows
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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.
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## How to run
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```bash
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javac iterator/*.java -d out/iterator
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java -cp out/iterator iterator.Main
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```
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Requires Java 25.
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## Post Section ↔ File Mapping
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| Post Section | File(s) |
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|---|---|
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| Custom Iterator Implementation — the Iterator interface | `BookIterator.java` |
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| Custom Iterator Implementation — the element type | `Book.java` |
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| Custom Iterator Implementation — the Aggregate (BookShelf, ForwardIterator, DecadeIterator) | `BookShelf.java` |
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| Custom Iterator Implementation — wiring it together | `Main.java` |
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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.
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Article: https://ankurm.com/iterator-design-pattern-java/
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All patterns: https://ankurm.com/design-patterns-java/
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