Behavioral Patterns Part 3: Iterator, Visitor, Memento, and Interpreter
Study patterns that help traverse object structures, add operations safely, capture state snapshots, and model small rule languages.
Inside this chapter
- Iterator Pattern
- Visitor Pattern
- Memento Pattern
- Interpreter Pattern
- Real-World Usage Snapshot
Series navigation
Study the chapters in order for the clearest path from first design principles to advanced Java architecture, framework usage, and interview-level pattern mastery. Use the navigation at the bottom of the page to move through the full tutorial smoothly.
Iterator Pattern
Iterator provides a standard way to traverse a collection without exposing its internal representation. Java developers use this pattern constantly through the Collections Framework, even when they do not name it explicitly.
List<String> names = List.of("Ana", "Bob", "Chen");
Iterator<String> iterator = names.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}Visitor Pattern
Visitor lets you define new operations over object structures without changing those element classes repeatedly. It is useful when element types are stable but operations vary. Compilers, AST processing, and reporting over model trees are common examples.
Memento Pattern
Memento captures and restores an object state snapshot without exposing internal details directly. Text editors, workflow rollback helpers, and undo features are common fits. In enterprise software, checkpointing and compensating transaction helpers sometimes reflect memento ideas.
Interpreter Pattern
Interpreter models grammar rules and evaluation logic for a small language. It is useful for expression evaluation, filtering rules, custom workflow syntax, or configuration-driven logic. For large languages, parser generators are usually better, but interpreter is still a good conceptual tool.
Real-World Usage Snapshot
Iterator is everywhere in Java APIs. Visitor appears in compilers and analyzers. Memento appears in rollback or draft-management features. Interpreter appears in rule engines and DSL-like configuration systems. Not every business application uses all of them, but advanced developers benefit from knowing when they fit.