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Neatbeans Debug, track changes to a variable

Posted on 2010-09-08
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Last Modified: 2013-12-14
I want to see a varaible change.  I right click and say 'add to watch' and only shows the current state it does not track its history of change?  Is there a debug tool that can do this and can work with NetBeans?
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Question by:RichardSDetsch
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Expert Comment

by:rockiroads
ID: 33632947
I have never come across a tool like that since the watch is usually to monitor the variable as you are stepping through code

why dont you try this, in the setter of that variable (assuming its a class variable), why dont you log the value being passed in.

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Expert Comment

by:rockiroads
ID: 33632953
in case you are not familiar with the logger in Java like log4j. you do not have to worry about removing logging code then when app goes live.
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Author Comment

by:RichardSDetsch
ID: 33633035
icecream flavs:
The variable is a private data member of a class of type double and my constructor sets it, but somehow by the time it gets to the classes toString method it gets changed to 0.0.   I am unfamiliar with this operation.   So if my class is below what would I do to log the value as being passed in its setter?

public class Class{
   private double trackVar;

   public Class(double trackVar){}

    public String toString(){print trackVar}

    public setTrackVar(double d){trackVar =d}
}

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Accepted Solution

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rockiroads earned 300 total points
ID: 33633065
add the logging in setTrackVar

public setTrackVar(double d) {
    LOG LINE HERE
    trackVar =d
}

if you are sure your constructor is setting it a value (which I assume is non zero) then something must be calling it. Tracing helps but you could put a breakpoint on the line trackVar = d then run your code in debug. Once it stops at that breakpoint you can check out the stack to see where it was called from
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Author Comment

by:RichardSDetsch
ID: 33633078
I am very new to this.  I will try this when I go to work tomorrow.  Thanks so much.
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LVL 65

Expert Comment

by:rockiroads
ID: 33633167
No problems.

If you dont want logging at this stage, just dump it using

System.out.println("Passed in value is " + d);

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Expert Comment

by:rockiroads
ID: 33633170
if u got time, have a look at log4j. http://www.vipan.com/htdocs/log4jhelp.html
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Expert Comment

by:__geof__
ID: 33634712
Can we get a look on your constructor and how it is called. It may be conversion problems i.e. if you try to set an int somewhere it won't do (like double = int/int doesn't work)
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Assisted Solution

by:gordon_vt02
gordon_vt02 earned 200 total points
ID: 33636871
Check your constructor and make sure you are setting this.trackVar and not just trackVar.  The 0.0 value is the default for doubles so it sounds like it isn't actually getting set in your constructor.
public Constructor(double trackVar) {
    // BAD -- Sets trackVar parameter, not class attribute
    trackVar = trackVar;

    // GOOD -- Sets trackVar class attribute to value of parameter
    this.trackVar = trackVar;
}

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Author Closing Comment

by:RichardSDetsch
ID: 33657442
These solutions are good practive.  Where you have a private variable that can only be acesses by setter functions.  But they do not track who called the setter and when.  
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