CODEWITHSUNDEEP
javaarraysdebuggingvariables
user843337
user843337

Reputation:

How can I check where a variable gets updated/changed in my code (java - eclipse)?

I'm having some problems debugging my code as I can't work out where an array is getting updated. I have looked through all my class files and I'm completely stumped as to what is happening.

At the moment I have a setup whereby I read in a csv file and store the contents in a 2D array (public static double[][] myArray). I then pass this array into a method whenever a user presses a button.

The weird thing is that it works fine the first time, however on all subsequent clicks of the button the data has changed and I can't work out why. I have searched through the code and there are absolutely no references to the original array (i.e. myClass.myArray = newArray) apart from where I pass it into the method.

Is there a reason this is happening? Alternatively please could someone suggest a way to track when the variable gets updated/changed?

Here is a brief overview of the code...

Read in the csv dataset and save it in a variable (ClassA):

public static double[][] myDataset;

// ...    

private static void readdDataset(String filePath)
{
    CsvReader reader = new CsvReader();
    myDataset = reader.readDataset(filePath, true);
}

This is the code used to set up the buttons' action:

button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) 
        {
            new RunProgram().execute(); // create a swing worker to run the code in bg
        }
});

Here is a condensed down version the code in the SwingWorker class:

protected Void doInBackground()
{
Config cfgFile = someClass.createConfigFile();
someOtherClass.runMyProgram(cfgFile, ClassA.myDataset);

    return null;
}

Finally here is the code to run the program:

public static void runRegression(Config cfgFile, double[][] dataset)
{   
    // Print out the first line in the array to see if it is the same every time (it should be!)
for(double value : dataset[0])
{
    System.out.print( value + " ");
}
System.out.println();

    // Do some other stuff....
}

Upvotes: 1

Views: 341

Answers (3)

JayCD
JayCD

Reputation: 57

So I can't really be sure what is going on for sure since you seem to be dealing with 2d object and classes and I have a very basic understanding on them.

However it sounds like your problem aren’t really the 2d aspects but the storage of the data it uses. It also sounds like your button is the problem or it's before the button gets pressed and since you haven't given us the code I don't think anyone can help you.

Try making a temp bypass for the button so it just auto fires once and see what happens.

As for the debugging the normal way is to say 

System.out.println("Array changed " + myArray[0] +" "+ myArray[1]  );

This will print in a line on the console

Array changed 1 4 (if myArray[0] == 0 and myArray[1] == 4)

I can't help you anymore without seeing some code and I don't think anyone else can help.

Upvotes: 0

ewan.chalmers
ewan.chalmers

Reputation: 16245

Every method you pass this array to has the opportunity to change its contents. Your array is not immutable.

Upvotes: 1

Dave Newton
Dave Newton

Reputation: 160261

From the outline or project view, right-click on the variable, and select "Toggle Watchpoint".

(You can also set conditional breakpoints, which is handy.)

There doesn't need to be a reference to the original array, any reference to a static (mutable) object can manipulate its contents.

Upvotes: 1

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