For developing a simple Java program following steps are mandatory :

1. First of all the JDK must be available in your system and its path must be located in the Environment variable if working on windows environment.
2. Then in the next step you must have a Java editor or a simple editor where you can write the Java program such as 'notepad'
3. Then in the next step when you are started to write a program there must be a class and either the public static void main(String[] args) method or static block must be available inside the class to execute the Java program.

The default value for int type local value is 0 (zero). For know about what are the keywords available in Java program go through the following link http://www.roseindia.net/java/example/java/core/hello-world-example.shtml

Class is a blueprint of similar objects : True

null is a keyword : false, null is not a keyword, it is a literal in java.