Allow the user to run the program step by step

Question

Hello, I am in the development part of my TCC that consists of a tool to support the teaching of graphs (more precisely of some algorithms, as Traveler Clerk, Minimum Generator Tree, etc...) and would like to allow the user to run the program in step-by-step mode, so that the user can control the execution of the algorithms and have time to observe the changes.

I would like suggestions on how to implement the step-by-step execution feature, whether there is a pattern, library, or if someone has already implemented something similar and could share the code for study.

Answer 1

There are two answers to what you want.

1. The simple answer consists of preparing the environment so that you show how to run the algorithm step by step but not implement a fully functional code Debugger. More or less like the one presented here on this page
2. The tricky answer is for you to get into JVM Bugger documentation website and try to understand how Debugger works. Or see how some simple debbuger implementation was done but I believe that’s not exactly what you’re looking for.

I recommend you use the first solution. Prepare previously each of the screens for each type of algorithm you want to run with buttons to start and go to next step. To run step by step an algorithm you need to deconstruct its loop and turn it into functions, for example:

Bubble Sort:

public static void bubbleSort(int[] array) {
    for (int j = 1; j < array.length; j++) {
        for (int i = 0; i < array.length - j; i++) {
            if (array[i] > array[i + 1]) {
                int tmp = array[i + 1];
                array[i + 1] = array[i];
                array[i] = tmp;
            }
        }
    }
}

You first need to extract the inside so:

public static void bubbleSort(int i , int[] array) {
    if (array[i] > array[i + 1]) {
        int tmp = array[i + 1];
        array[i + 1] = array[i];
        array[i] = tmp;
    }
}

Now you need to put the correct inputs for this part simulating the execution. Follow full example to give you an idea:

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

public class Sorter {

    public static void main(String[] args) {

        final int[] array = {5, 2, 4, 6, 1, 3};
        final List<Integer> contextValues = new ArrayList<Integer>();

        for (int j = 1; j < array.length; j++) {
            for (int i = 0; i < array.length - j; i++) {
                contextValues.add(i);
            }
        }
        System.out.print("Array:");
        printArray(array);
        System.out.println();
        //executa a cada 1 segundo um passo do bubble sort
        final Timer t = new Timer();
        t.scheduleAtFixedRate(new TimerTask() {
            int step = 0;

            @Override
            public void run() {
                System.out.println("--------------");
                System.out.println("Passo " + step);
                bubbleInPosition(array, contextValues.get(step));
                printArray(array);

                if (step > contextValues.size()) {
                    t.cancel();
                }
                step++;
            }
        }, 0, 1000);

    }

    public static void printArray(int array[]) {
        System.out.print("[");
        for (int i : array) {
            System.out.print(" " + i + " ,");
        }
        System.out.print("]");
    }

    private static void bubbleInPosition(int[] array, int i) {
        if (array[i] > array[i + 1]) {
            int tmp = array[i + 1];
            array[i + 1] = array[i];
            array[i] = tmp;
        }
    }
}

In place of Timer you would have called the next step button. This would be a simple idea, but can be applied to various algorithms.