Static Blocks and Variables

Question

Why is the value of a valid static variable assigned in the code below, but not using the same variable?

class Test { static { var=2; //There is no error in this line System.out.println(var); //Why is there an error on this line if no error on the above line } static int var; } 

Answer 1

Because usage is not on the left side of the assignment , as described below:

From section 8.3.2.3 JLS, Restrictions on the use of fields during initialization :

A member declaration must appear before its use only if the member is an instance (respectively static) field of a class or interface C and all of the following conditions are true:

• Use occurs in an instance variable (respectively static)
  C initializer or in an instance (respectively static) initializer
  from C.

• Use is not on the left side of the quest.

• C is the innermost class or interface that spans usage.

A compile-time error occurs if any of the three requirements above are not satisfied.

Answer 2

Error: Test.java:6: illegal forward reference . Move int var in front of the static block.

Answer 3

Try it like this:

 class Test { static int var; static { var=2; //There is no error in this line System.out.println(var); //Why is there an error on this line if no error on the above line } } 

With announcement before use