According to the spec,

If the declarator is for an instance variable (that is, a field that is not static) of a value class (8.1.1.5), then the initializer is an early instance variable initializer and occurs in an early construction context (8.8.7.1); the initializer may refer to any class variable of the class, even one whose declaration occurs to the right of the initializer. At run time, the initializer is evaluated and the assignment performed each time an instance of the class is created, at the start of the class's construction process (12.5).

The following cases should therefore fail with a compilation error:

value class C {

    int b = this.a;

    int a;

    C() {
        a = 5;
    }
}
 
    public static void main(String[] args) {
        C c = new C();
        System.out.println(c.b);
    }
 
 
Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    C.<init>()V @7: getfield
  Reason:
    Type uninitializedThis (current frame, stack[1]) is not assignable to 'C'
  Current Frame:
    bci: @7
    flags: { flagThisUninit }
    locals: { uninitializedThis }
    stack: { uninitializedThis, uninitializedThis }
  Bytecode:
    0000000: 2a08 b500 012a 2ab4 0001 b500 072a b700
    0000010: 0ab1
 
                at Main.main(Main.java:3)


Case 2: instance variable declarator refers to another variable via this, no constructor

value class C {
    int a = 5;
    int b = this.a;

}

    public static void main(String[] args) {
        C c = new C();
        System.out.println(c.b);
    }
Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    C.<init>()V @7: invokestatic
  Reason:
    Type uninitializedThis (current frame, stack[1]) is not assignable to 'java/lang/Object'
  Current Frame:
    bci: @7
    flags: { flagThisUninit }
    locals: { uninitializedThis }
    stack: { uninitializedThis, uninitializedThis }
  Bytecode:
    0000000: 2a08 b500 012a 2ab8 0007 5708 b500 0d2a
    0000010: b700 10b1
 
                at Main.main(Main.java:3)
 
Case 3: instance variable declarator refers to another instance variable.


value class C {
    int b = a;
    int a = 5;

}

    public static void main(String[] args) {
        C c = new C();
        System.out.println(c.b);
    }

 
Compilation succeeds and and the result will print 5.