Using Exception Breakpoints in WDSc

April 7, 2004 Hey, David

I have only been using WDSc (WebSphere Development Studio client) for a few weeks, so this may be an obvious question. How would you watch a variable in a Java program? Is there some way to trace a value or break when a certain condition is met? I hit F8 to run to my break point and hover the mouse over a variable to see its value. I just spent about two hours repeating this procedure to find out why my program was receiving a null pointer exception, even though I knew from the stack trace exactly what line the program was failing on.

–Neil

The debugger in WDSc is amazingly powerful. One useful feature that is easy to miss is the ability to set exception break points. An exception break point causes a running program to stop execution, allowing you to inspect variables and diagnose a problem. To add an exception breakpoint select Add Java Exception Breakpoint from the Run drop-down menu.

You can also add conditional break points and watch a value. Double-click the left border area of the line where you want your breakpoint. A blue bullet will appear, indicating that a breakpoint is set for the line. After setting the breakpoint, right-click the blue bullet and select Breakpoint Properties. . . . The Java Line Breakpoint Properties dialog will appear. Check the Enable Condition checkbox and enter a condition that resolves to a true Boolean value. That condition can be as simple as myString.equals(“value”), or a complex condition. The code you enter in this box is nearly unlimited and will be aware of program variables in the executing program. I have even used this dialog to log values to the console, using System.err.println(myString).

The Java Line Breakpoint Properties dialog

You can also use the Java line breakpoint properties dialog to set a breakpoint when a value changes, by selecting the Suspend when value of condition changes radio button.

Now that you know where to find these debug features, I bet your future debugging will go much more quickly.

–David