What is the difference between a JDK and a JVM?

JDK is Java Development Kit which is for development purpose and it includes execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.
or

JDK is the java development kit contains the executable 
files.
JRE is the java run time envirnment contains all the 
runtime jar files.
JVM is the java virtual machine which is used to convert 
the byte code to user understandable code

thus we can say that jvm is a specification and jre is a implementer.

Regards:

vinitkar Tripathi