Interpreter Design Pattern — Java Example
Pattern: Behavioral → Interpreter Article: https://ankurm.com/interpreter-design-pattern-java/
What this example shows
A math expression evaluator built as an abstract syntax tree. Expression declares interpret() — every AST node implements it. NumberExpression is the only terminal: a leaf with no children that returns its value directly. AddExpression, SubtractExpression, and MultiplyExpression are non-terminals: each holds two child expressions and applies its operator after recursively interpreting them. Main is the client — it assembles three small trees by hand ((5 + 3) * 2, 10 - (4 + 2), (3 * 4) + (10 - 6)) and evaluates each by calling interpret() on the root.
How to run
javac interpreter/*.java -d out/interpreter
java -cp out/interpreter interpreter.Main
Requires Java 25.
Post Section ↔ File Mapping
| Post Section | File(s) |
|---|---|
| Implementation: Math Expression Evaluator — the AbstractExpression | Expression.java |
| Implementation: Math Expression Evaluator — the TerminalExpression | NumberExpression.java |
| Implementation: Math Expression Evaluator — AddExpression | AddExpression.java |
| Implementation: Math Expression Evaluator — SubtractExpression | SubtractExpression.java |
| Implementation: Math Expression Evaluator — MultiplyExpression | MultiplyExpression.java |
| Implementation: Math Expression Evaluator — wiring it together | Main.java |
Article: https://ankurm.com/interpreter-design-pattern-java/ All patterns: https://ankurm.com/design-patterns-java/