Stack overflow error on Recursive Syntax lab homework

Question

A lot of posts exist on this assignment - most wanting to know how to do it. Please let me figure out the rest of this on my own - I'm just looking for one or two bits of help, not someone to do my assignment for me.

The assignment is to write a program that implements syntax rules to build random sentences.

When I implement my code, I get a stack overflow, but I modeled it after the sample code that doesn't have that error. I know it's something with my if...else statement in sentence(); causing it.

Here is my code:

import java.util.Random;
import java.util.ArrayList;
import java.util.List;


public class RecursiveSyntax {

    private static final String[] conjunction = { "and", "or", "but", "because" };
    private static final String[] properNoun = { "Fred", "Jane", "Richard Nixon", "Miss America" };
    private static final String[] commonNoun = { "man", "woman", "fish", "elephant", "unicorn" };
    private static final String[] determiner = { "a", "the", "every", "some" };
    private static final String[] adjective = { "big", "tiny", "pretty", "bald" };
    private static final String[] intransitiveVerb = { "runs", "jumps", "talks", "sleeps" };
    private static final String[] transitiveVerb = { "loves", "hates", "sees", "knows", "looks for", "finds" };

       public static void main(String[] args) {



           List<String[]> arrayList = new ArrayList<>();
           arrayList.add(conjunction);
           arrayList.add(properNoun);
           arrayList.add(commonNoun);
           arrayList.add(determiner);
           arrayList.add(adjective);
           arrayList.add(intransitiveVerb);
           arrayList.add(transitiveVerb);



              while (true) {
                 sentence();
                 System.out.println(".\n\n");
                 try {
                     Thread.sleep(3000);
                 }
                 catch (InterruptedException e) {
                 }
              }
           }







    private static void sentence() {
        int c = (int)(Math.random()*conjunction.length);
        double x = Math.random();
        if (x < 0.2)
            simpleSentence();
        else 
            simpleSentence();
            System.out.print(conjunction[c]);
            sentence();


        }



        private static void simpleSentence() {
            nounPhrase();
            verbPhrase();

        }


        private static void nounPhrase() {
            int pn = (int)(Math.random()*properNoun.length);
                System.out.print(" "+  properNoun[pn] + " ");

        }

        private static void verbPhrase() {
            int iv = (int)(Math.random()*intransitiveVerb.length);
            System.out.print(" " +  intransitiveVerb[iv]);

        }


    }

I'm just looking for two things:

1. How do I fix my stack overflow error
2. What am I doing wrong with my if..else statement?

I need it to call simpleSentence() some of the time, and on a random weighted percent of the time call simpleSentence, then print a random conjunction from the conjunction array, then run sentence() again without stack overflow errors.

The BNF for this part is:

<sentence> ::= <simple_sentence> [ <conjunction> <sentence> ]
<simple_sentence> ::= <noun_phrase> <verb_phrase>

A copy of the assignment requirements can be found here (if it's needed for clarity) Par 1 Recursive Syntax: http://math.hws.edu/eck/cs225/s10/lab3/.

Answer 1

No, sentence will call itself 100% of the time... this is not python, and therefore your indents are misleading. You need to do else { simpleSentence(); ... sentence() }. As written, only the first statement after the else is part of it. – Foon

This solved it perfectly! Thanks Foon!!