java : accessing static variables inside static block

Question

Analyzing some weird scenarios in following static block :

static {
  System.out.println("Inside Static Block");
  i=100; // Compilation Successful , why ?
  System.out.println(i); // Compilation error "Cannot reference a field before it is defined"
}

private static int i=100;

While same code is working fine while using :

static {
  System.out.println("Inside Static Block");
  i=100; // Compilation Successful , why ?
  System.out.println(MyClass.i); // Compiles OK
}

private static int i=100;

Not sure why variable initialization do not need variable access using class name while SOP requires ?

@Bohemian I think this is a copy/paste fail. The second block shouldn't show errors. — Alexis C.
– Alexis C., Commented May 19, 2013 at 13:49

assylias · Accepted Answer · 2019-03-19 08:23:03Z

16

This is because of the restrictions on the use of Fields during Initialization. In particular, the use of static fields inside a static initialization block before the line on which they are declared can only be on the left hand side of an expression (i.e. an assignment), unless they are fully qualified (in your case MyClass.i).

So for example: if you insert int j = i; right after i = 100; you would get the same error.

The obvious way to solve the issue is to declare static int i; before the static initialization block.

edited Mar 19, 2019 at 8:23

answered May 19, 2013 at 13:41

assylias

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4 Comments

Bohemian Over a year ago

+1 Cool. I didn't know that, nor have I encountered it. Also I can't believe it's taken me this long to figure out your name :/

assylias Over a year ago

It actually is a coincidence but nice one anyway!

Hearen Over a year ago

@assylias Sorry for any inconvenience, I tested it locally only in that way, the >>same error<< can occur.

assylias Over a year ago

Yes agreed, for the same reason.

micho · Accepted Answer · 2013-05-19 13:57:01Z

0

this is because compilers doing static code analysis, for example the live variable analysis (backward analyze). It calculates for each program point whether the variable will be read before the next write.

answered May 19, 2013 at 13:57

micho

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