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Thread: Methodology to find bugs

  1. #1
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    Default Methodology to find bugs

    Ive writen the following class. The point of the code can be found here Problem 12 - Project Euler.

    The code doesn't work!!! But before anybody points out why, I wanted to ask about technics and methods that people use to try to find bugs. I have learnt about 'asserts' but I can't quite get my head around how I could use them in this case.

    Currently the code just outputs the answer 1... no matter what I enter as the args!!!

    public class TriangleFinder implements Runnable {
    	public long target;		// number to divisors
    	public long outputValue;
    	public boolean finished = false;
    	private Thread runner;
     
    	TriangleFinder(long inTarget) {
    		target = inTarget;
    		if (runner == null) {
    			runner = new Thread(this);
    			runner.start();
    		}
    	}
     
    	public void run() {
    		long numOfDivisors = 0;
    		for (long i = 1; i < target; i++) {
    			outputValue = getDivisors(getTriangle(i));
    		}
    		finished = true;
    	}
     
    	public long getTriangle(long checkNum) {
    		long triangleValue = 0;
    		for (long i = checkNum; i > 0; i--) {
    			triangleValue += i;
    		}
    		return triangleValue;
    	}
     
    	public long getDivisors(long checkDiv) {
    		int divisorCount = 0;
    		for (long i = 1; i <= checkDiv; i++) {
    			if (i % checkDiv == 0) {
    				divisorCount++;
    			}
    		}
    		return divisorCount;
    	}
    }

    Thanks
    Last edited by tarkal; October 9th, 2011 at 03:13 PM.


  2. #2
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    Default Re: Methodology to find bugs

    I wanted to ask about technics and methods that people use to try to find bugs.
    Debugging with the debugger supplied via jdb or any number of IDE's available. You can step through the code to evaluate variable values. In addition, using assertions or writing Test cases help you break problems down and make sure pieces of code work as they are expected to work. Throwing runtime exceptions for things such as illegal parameters is also valuable.

    Currently the code just outputs the answer 1... no matter what I enter as the args!!!
    Since there is no main method, hence no args, it is difficult to advise you. Please provide an SSCCE that demonstrates the problem.

  3. #3
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    Default Re: Methodology to find bugs

    Hi sorry for the late reply. here is the class with the main method that instantiates the above class.

    public class TriangleThreads {
    	public static void main(String[] args) {
    		TriangleThreads tt = new TriangleThreads(args);
    	}
     
    	public TriangleThreads(String[] args) {
    		TriangleFinder[] finder = new TriangleFinder[args.length];
     
    		for (int i = 0; i < args.length; i++ ) {
    			try {
    				long count = Long.parseLong(args[i]);
    				finder[i] = new TriangleFinder(count);
    				System.out.println("Looking...");
    			} catch (NumberFormatException nfe) {
    				System.out.println("Error " + nfe.getMessage());
    			}
    		}
     
    		boolean complete = false;
    		while (!complete) {
    			complete = true;
    			for (int j = 0; j < finder.length; j++) {
    				if (finder[j] == null) continue;
    				if (!finder[j].finished) {
    					complete = false;
    				} else {
    					displayResults(finder[j]);
    					finder[j] = null;
    				}
    			}
     
    			try {
    				Thread.sleep(1000);
    			} catch (InterruptedException ie) {
    				// do nothing
    			}
    		}
    	}
     
    	private void displayResults(TriangleFinder finder) {
    		System.out.println("The first triangle number to have " + finder.target + " divisors is " + finder.outputValue );
    	}
    }
    Last edited by tarkal; October 10th, 2011 at 02:20 PM. Reason: Entered wrong code

  4. #4
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    Default Re: Methodology to find bugs

    I'm now 90% sure that the problem is coming from the run()...

  5. #5
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    Default Re: Methodology to find bugs

    aha... I have found that a good way of isolating a problem is to ad in tempory variables and print them out to see what is happening. Is this generaly an accepted technique?

  6. #6
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    Default Re: Methodology to find bugs

    I've managed to solve the problem and fix the code (below) but for numbers larger than 400 it becomes very very slow. Any suggestions on how this could be enhanced for larger numbers?
    public class TriangleFinder implements Runnable {
    	public long target;		// number to divisors
    	public long outputValue;
    	public boolean finished = false;
    	private Thread runner;
     
    	TriangleFinder(long inTarget) {
    		target = inTarget;
    		if (runner == null) {
    			runner = new Thread(this);
    			runner.start();
    		}
    	}
     
    	public void run() {
    			for (long i = 0; getDivisors(getTriangle(i)) < target; i++) {
    				outputValue = getTriangle(i + 1);
    			}
    		finished = true;
    	}
     
    	public long getTriangle(long checkNum) {
    		long triangleValue = 0;
    		for (long i = checkNum; i > 0; i--) {
    			triangleValue += i;
    		}
    		return triangleValue;
    	}
     
    	public long getDivisors(long checkTri) {
    		long divisorCount = 0;
    		for (long i = 1; i <= checkTri; i++) {
    			if (checkTri % i == 0) {
    				divisorCount++;
    			}
    		}
    		return divisorCount;
    	}
    }
    Last edited by tarkal; October 10th, 2011 at 04:07 PM.

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