The Definitive ANTLR 4 Reference, 2nd Edition

Implementing Applications with Visitors

To use a visitor instead of a listener, we ask ANTLR to generate a visitor interface, implement that interface, and then create a test rig that calls visit on the parse tree. We don’t have to touch the grammar at all.

When we use the -visitor option on the command line, ANTLR generates interface PropertyFileVisitor and class PropertyFileBaseVisitor, which has the following default implementations:

public class PropertyFileBaseVisitor<T> extends AbstractParseTreeVisitor<T>
    implements PropertyFileVisitor<T>
{
    @Override public T visitFile(PropertyFileParser.FileContext ctx) { ... }
    @Override public T visitProp(PropertyFileParser.PropContext ctx) { ... }
}

We can copy the map functionality ...