Additional debug option for runnable jar using command prompt

Question

I know that the java -jar filename.jar is used for executing the jar file using command prompt, but could anyone please explain the following command:

java -jar filename.jar -debug

What is the exact use of the -debug in the above command?

Answer 1

This is not a flag for the Java Interpreter (as those should be passed before the actual class/jar).

If you execute the command-line you posted above, this will launch your filename.jar -files main class and give it's main(String[] args) -method the -debug -parameter as the second argument in the args -array.

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But, there is (or was) also the -debug flag from older Java versions, which has been replaced by the -Xdebug flag . The (certainly old) manpage states that:

-debug Allows the Java debugger - jdb(1) - to attach itself to this java session. When -debug is specified on the command line java displays a password that must be used when starting the debugging session.

If a Java application is launched with the debug flag, remote-debuggers can attach to the running application and you can (for example) monitor it using JConsole