Using the Java Debugger

This page is generally correct but needs some work before it will be accessible to a large number of CS5 students. If you've had experience using a debugger in the past, the page might be fine as is.

The Integrated Development Environments (IDEs) we use in this class either don't handle the debugger at all (JCreator) or don't handle it when input from the keyboard is needed (Xcode). Since we only write console applications in CS5, if you wish to use the debugger on a program that receives standard input, some magic is needed.

Using the Debugger with Command Line Applications with Standard I/O

Open two command windows:

• Windows-XP: right click on the Start Icon and select the Run icon. Enter cmd. To get a 2nd window, repeat this procedure again.
• Mac OSX: open the Finder and navigate to Applications->Utilities. Clicking on Terminal will open a command window. To get the 2nd, repeat.

Note: If you're running this from your dorm computer and it is a PC, you'll need to make sure that your path is properly set (as described here).

Debugging the program:

• In the first command window, cd to your requisite source_code directory.


• Recompile the program with the debugging option:

  javac -g CS5App.java



• Run the program in debugging mode:

     java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=4571 CS5App
  

  This window provides your program with standard I/O.


• In the other command window, type:

     jdb -connect com.sun.jdi.SocketAttach:hostname=localhost,port=4571
  

  This window provides your access with the debugger, which can then be used to step through your code and view its behavior in a variety of ways.


• The Java debugger is not the friendliest beast to use. For a summary of commands you can type ? (but that produces a lot of options!). This link provides a decent Java Debugger tutorial, and this link provides a quick summary of useful commands.

Good Luck, Have Fun, and ask questions if you have any!