JDB the Java Debugger which comes with the OpenJDK

1) open two terminal shell window
(terminal menu bar : open new window)
go in ~/java/myclass with the two shell terminal window
(JDB needs to read the source code file .java in the same folder)

2) launch the first processus in a VM in the first shell terminal
>java -agentlib:jdwp=transport=dt_socket,server=y,suspend=y MaPremiereClassJava

3) launch the second processus in the second shell terminal
>jdb -attach 49251
(here 49251 is the same port number given by java in 2))

after jdb is correctly connected to the VM
type the following commands inside jdb

main[1] step
main[1] list
main[1] step
main[1] list
main[1] cont