1. 1First BlueJ Day, Houston, Texas, 1st March 2006 Debugging in BlueJ Davin McCall

2. 2First BlueJ Day, Houston, Texas, 1st March 2006 Overview What is debugging? Object inspector Method invocation “Traditional” BlueJ debugger window Demo Questions

3. 3First BlueJ Day, Houston, Texas, 1st March 2006 Debugging… Locate the source of a bug Run through the part of the program where we think the bug is occurring, watch program behaviour In BlueJ this is normal operation!! (to some extent) - inspectors, method invocation BlueJ also has a (simple) more traditional debugger

4. 4First BlueJ Day, Houston, Texas, 1st March 2006 Debugging (cont’d) Set “breakpoints” which will halt the program execution when reached Once execution is halted, can continue execution line by line (“stepping”), either following or stepping over function calls Inspect values of variables in currently executing methods (the stack). Inspected objects shown in familiar inspector windows

5. 5First BlueJ Day, Houston, Texas, 1st March 2006 Stepping Stepping through code … Might let us see what is going wrong Also serves as a good way to demonstrate control structure behavior, program flow, etc

6. 6First BlueJ Day, Houston, Texas, 1st March 2006 BlueJ as a debugger Even without the debugger window, BlueJ offers unique features which can be used for debugging and testing Construct objects on the fly Call arbitrary methods interactively Inspect objects and classes to see field values

7. 7First BlueJ Day, Houston, Texas, 1st March 2006 Conclusion BlueJ provides basic debugging functionality Some of BlueJ’s core features (interactive invocation and inspection) are also useful for debugging Debugging techniques can serve another purpose: demonstrating code behaviour