Headline

Parsing text to trees and walk them with ANTLR4 Listeners

Realtionships

This an ANTLR4 version of Contribution:antlrTrees using the Listener pattern.

Illustration

Total and Cut are implementations of the CompanyBaseListener using the listener pattern (Observer pattern). To execute Cut or Total the walk method of an instance of ParseTreeWalker is used. The Listener to execute is given as an argument to walk.

An example from TotaListenerTest:

    ParseTreeWalker walker = new ParseTreeWalker();
    TotalListener extractor = new TotalListener(parser);
    walker.walk(extractor, tree);
    System.out.println("Total = " + extractor.getTotal());
The variable tree conatins the ParseTree of the company.

An example from the TotalListener:

public class TotalListener extends CompanyBaseListener {
    private float total = 0;

    //skip uninteresting part 

    public float getTotal() {
      return total;
    }
    @Override
    public void enterEmployee(@NotNull CompanyParser.EmployeeContext ctx) {
        // All FLOATS are salaries
        total += Float.parseFloat(ctx.FLOAT().getText());
    }
}

Usage

This contribution uses Technology:Gradle for building. Technology:Eclipse is supported.

See https://github.com/101companies/101simplejava/blob/master/README.md

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