Is there a way to know if a Java program was started from the command line or from a jar file?

Question

I want to either display a message in the console or a pop up, so in case a parameter is not specified, I want to know to which should I display

Something like:

Answer 1

I'm not clear on the question but I'm going to interpret it as you want to differentiate between the following 2

java -jar fred.jar

and

java package.Main

Here is an outline line of the program

import sun.jvmstat.monitor.*;
...
HostIdentifier hostId = new HostIdentifier("localhost");
MonitoredHost monitoredHost = MonitoredHost.getMonitoredHost(hostId);
Set jvms = monitoredHost.activeVms();
for (Object i: jvms) {
   VmIdentifier id = new VmIdentifier("//" + i + "?mode=r");
   MonitoredVm vm = monitoredHost.getMonitoredVm(id, 0);   
   System.out.println(i);
   System.out.println("\t main class: " + MonitoredVmUtil.mainClass(vm, false));
   System.out.println("\t main args: " + MonitoredVmUtil.mainArgs(vm));
   System.out.println("\t jvmArgs: " + MonitoredVmUtil.jvmArgs(vm));
   monitoredHost.detach(vm);
}

The call MonitoredVmUtil.mainClass(vm, false) will either return 'jar' or the name of your main class eg Main.

You have to use $JAVA_HOME/lib/tools.jar to compile and run.