What is static in java ?

Static means one per class, not one for each object no matter how many instance of a class might exist.
This means that you can use them without creating an instance of a class.
Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object.

A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final.
However, you can't override a static method with a non static method. In other words, you can't change a static method into an instance method in a subclass.