jdb

If the compiler returns errors related to your code, you can use the Java debugger to debug your code. The most common way to start jdb on local classes is using the following syntax:

    jdb classname [parameters]

To run the debugger, you are substituting the command for Java with jdb. This starts the Java interpreter with the class to be debugged and any specified parameters, and stops before executing the class's first process.

If you need to run jdb with Java interpreter already running, you can connect to the interpreter using the -host and -password options. In order to be able to retrieve the password from the Java interpreter session, it must have been invoked using the -debug option. When you start Java using the -debug option, it provides a password with which the jdb can be started.

You can feed the Java debugger several command-line parameters that change its behavior. These parameters can be listed using jdb's help parameter. Below Table lists all of these commands.

Option	Function
catch classID	Breaks for the specified exception.
Classes	Lists currently known classes.
clear classID:line	Clears a breakpoint.
Cont	Continues execution from breakpoint.
down [n frames]	Moves down a thread's stack.
dump ID [ID..]	Prints all object information.
exit (or quit)	Exits debugger.
help (or ?)	Lists commands.
ignore classID	Ignores the specified exception.
list [line number]	Prints source code.
load classname	Loads class.
locals	Prints all local variables in current stack frame.
memory	Reports memory usage.
methods	Lists methods in a class.
print ID [ID..]	Prints an object or field.
resume [threadID..]	Resumes threads. Default is all.
run class [args]	Starts execution of a loaded class.
step	Executes current line.
stop in classID.method	Sets a breakpoint in a method.
stop at classID:line	Sets a breakpoint at a line.
suspend [threadID..]	Suspends threads. Default is all.
threads threadgroup	Lists threads.
thread threadID	Sets default thread.
threadgroups	Lists threadgroups.
threadgroup name	Sets current threadgroup.
up [n frames]	Moves up a thread's stack.
use [path]	Displays or changes source path.
where [threadID] or all	Dumps a thread's stack.
!!	Repeats last command.

Below Table lists the command-line options for jdb that are used when accessing a running interpreter.

Command	Function
-host <hostname>	Sets the name of the host machine on which the interpreter session to attach to is running.
-password <password>	Logs in to the active interpreter session. This is the password printed by the Java interpreter. The password prints when invoked by the -debug option.