If I specify a System property multiple times when invoking JVM which value is used?

Question

If I specify a system property multiple times when invoking the JVM which value will I actually get when I retrieve the property? e.g.

java -Dprop=A -Dprop=B -jar my.jar

What will be the result when I call System.getProperty("prop");?

The Java documentation on this does not really tell me anything useful on this front.

In my non-scientific testing on a couple of machines running different JVMs it seems like the last value is the one returned (which is actually the behavior I need) but I wondered if this behavior is actually defined officially anywhere or can it vary between JVMs?

Answer 1

There's nothing like writing a little class to see how it works.

public class PropTest {

  public static void main(String[] args) {
    System.out.println(System.getProperty("prop"));
  }

}

Which when compiled and ran with the command line

java -Dprop=A -Dprop=B -Dprop=C PropTest

yeilds the output

C

Which would imply that the values are put into the table left to right, with the last value overwriting previous values.

Just to make a note of the environment, Fedora 16, Linux 3.3.7, 64 bit

> java -version

java version "1.6.0_24"
OpenJDK Runtime Environment (IcedTea6 1.11.1) (fedora-65.1.11.1.fc16-x86_64)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)