Tag: initialization

Why does this code compile with explicit static field notation on the right hand side, but not without ?

public class A
{
    static int a = ++A.a;  // compiles
    //static int a = ++a;  // error - cannot reference a field before it is defined

    public static void main(String[] args) {
        System.out.println(a);
    }
}

Solution:

This is simply how the language spec is written. Specifically, Sec 8.3.3 says:

References to a field are sometimes restricted, even through the field is in scope. The following rules constrain forward references to a field (where the use textually precedes the field declaration) as well as self-reference (where the field is used in its own initializer).

For a reference by simple name to a class variable f declared in class
or interface C, it is a compile-time error if:

• …

Emphasis mine.

A.a is not a simple name, so it’s not a compile-time error.