You don't need JDK
to run Java based programs. JDK
is for development which stands for Java Development Kit
.
You need JRE
which should be there in Mac.
Try: java -jar Myjar_file.jar
EDIT: According to this article, for Mac OS 10
The Java runtime is no longer installed automatically as part of the OS installation.
Then, you need to install JRE to your machine.