There are more ways to run Java programs (either .class or .jar). One is to use the executable named java and the other is to use javaw.\ So what is the difference?
java (java.exe on Windows) runs the program in a console window. If you run the command
java -jar Application.jar
then a console window appears (if not already done in a console) and the program uses it for the input and standard output and standard error streams.
On the contrary, javaw or javaw.exe runs the program without console window appearing, and all input and output (using e.g. System.out.println() or System.err.print()`) is silenced.
So, if you have the same problem I had, that is, running the .jar file in a windows console (cmd.exe) and having no output, then you can fix that by changing the Windows registry value HKEY_CLASSES_ROOT\jarfile\shell\open\command. In my case, its value is:
HKEY_CLASSES_ROOT\jarfile\shell\open\command = "C:\sw\Java\jre1.6.0_07_32bit\bin\javaw.exe" -jar "%1" %*
Just change the javaw.exe to java.exe. After changing, you will see the output in the console when running .jar files just by „double-clicking“ it.