Visitor pattern example

VisitorOld.java

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package visitorchallenge;

import ast.Exp;
import ast.MulExp;
import ast.NegExp;
import ast.NumberLiteral;
import ast.SumExp;
import ast.Visitor;

/**
 *
 * @author danilo
 */
public class VisitorOld {

    public static void main(String[] args) {
        Visitor<None> v = new Visitor<None>() {
            @Override
            public None visit(NumberLiteral nl) {
                print(nl.value());
                return NONE;
            }

            @Override
            public None visit(NegExp nl) {
                print("(- ");
                nl.exp().accept(this);
                print(")");
                return NONE;
            }

            @Override
            public None visit(MulExp nl) {
                print("(* ");
                nl.left().accept(this);
                print(" ");
                nl.right().accept(this);
                print(")");
                return NONE;
            }

            @Override
            public None visit(SumExp nl) {
                print("(+ ");
                nl.left().accept(this);
                print(" ");
                nl.right().accept(this);
                print(")");
                return NONE;
            }
        };

        Exp exp = new SumExp(new SumExp(new NumberLiteral(1.0), new NegExp(new NumberLiteral(10))), new MulExp(new NumberLiteral(10.0), new NumberLiteral(20)));

        exp.accept(v);
    }

    private static None NONE = new None();

    private static void print(Object o) {
        System.out.print(o);
    }

    static class None {

    }
}