Can a abstract class be declared final?

Not possible. An abstract class without being inherited is of no use and hence will result in compile time error.

Can we declare a static variable inside a method?

Static varaibles are class level variables and they can't be declared inside a method. If declared, the class will not compile.

What is an Abstract Class and what is it's purpose?

A Class which doesn't provide complete implementation is defined as an abstract class. Abstract classes enforce abstraction.

What is the importance of static variable?

static variables are class level variables where all objects of the class refer to the same variable. If one object changes the value then the change gets reflected in all the objects.

I want to print "Hello" even before main is executed. How will you acheive that?

Print the statement inside a static block of code. Static blocks get executed when the class gets loaded into the memory and even before the creation of an object. Hence it will be executed before the main method. And it will be executed only once.

When will you define a method as static?

When a method needs to be accessed even before the creation of the object of the class then we should declare the method as static.

What are the restriction imposed on a static method or a static block of code?

A static method should not refer to instance variables without creating an instance and cannot use "this" operator to refer the instance.