Visitor pattern revisited

VisitorAlternative.java

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 */
package visitorchallenge;

import ast.Exp;
import ast.MulExp;
import ast.NegExp;
import ast.NumberLiteral;
import ast.SumExp;
import java.util.HashMap;
import java.util.Map;

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

    static Map<Class, Funct<? extends Exp, Void>> map;

    static {
        map = new HashMap<>();

        map.put(SumExp.class, (SumExp e) -> {
            System.out.println("SumExp.");
            return null; //To change body of generated lambdas, choose Tools | Templates.
        });

        map.put(MulExp.class, (MulExp e) -> {
            System.out.println("MulExp  .");
            return null; //To change body of generated lambdas, choose Tools | Templates.
        });
    }

    static <T extends Exp> void apply(T t) {
        Funct<T, Void> f = (Funct<T, Void>) map.get(t.getClass());

        f.apply(t);
    }

    public static void main(String[] args) {
        final SumExp exp = new SumExp(
                new SumExp(
                        new NumberLiteral(1.0),
                        new NegExp(new NumberLiteral(10))),
                new MulExp(
                        new NumberLiteral(10.0),
                        new NumberLiteral(20)));

        Exp exp1 = exp.left();
        Exp exp2 = exp.right();

        apply(exp1);
        apply(exp2);
    }

    interface Funct<T, V> {

        V apply(T t);
    }
}