JDK

what is JDK?
JDK is a complete software package used to develop java application.
It contains tools to write, compile, debug, and run java programs.

when is JDK used?
=> when you are writing Java code.
=> when you are compiling Java program.
=> During Development time.

How JDK used?
you write .java file
use javac(compiler from JDK) to convert it to .class file
Run the program using java command

Example
javac Hello.java
java Hello