Name: tb29552 Date: 05/02/2001


/*
java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0-C)
Java HotSpot(TM) Client VM (build 1.3.0-C, mixed mode)


Whenever the qualifying primary to a static field or method
reference is itself a qualified instance field reference, javac
1.3 is emitting invalid classfiles. The compiler is overly
optimizing on the fact that the qualifying expression of a static
reference needs to only be evaluated for side effects, by
incorrectly assuming that the instance field reference has no
side effects. According to JLS 15.12.4.1 and 15.11.1, the
Primary must be evaluated and the value discarded before
accessing the static field or method; and by 15.11.1, evaluation
of the instance field can throw a NullPointerException.

This program demonstrates the errant behavior:

$ cat Foo.java */
class Foo {
    static Foo s = null; // in correct code, will cause
                                // NullPointerExceptions
    Foo i;
    static byte b;
    static void bar() {
        System.out.println("Oops");
    }
    public static void main(String[] args) {
        try {
            s.i.bar();
        } catch(NullPointerException npe) {
            System.out.println("OK");
        }
        try {
            s.i.b++;
            System.out.println("Oops");
        } catch(NullPointerException npe) {
            System.out.println("OK");
        }
    }
}
/*
$ javac Foo.java
$ java Foo
Oops
Oops
$ javap -c Foo
Compiled from A.java
class Foo extends java.lang.Object {
    static Foo s;
    Foo i;
    static byte b;
    Foo();
    static void bar();
    public static void main(java.lang.String[]);
}

Method Foo()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 return

Method void bar()
   0 getstatic #2 <Field java.io.PrintStream out>
   3 ldc #3 <String "Oops">
   5 invokevirtual #4 <Method void println(java.lang.String)>
   8 return

Method void main(java.lang.String[])
   0 getstatic #5 <Field Foo s>
// missing getinstance <Field Foo i>
   3 pop
   4 invokestatic #6 <Method void bar()>
   7 goto 19
  10 astore_1
  11 getstatic #2 <Field java.io.PrintStream out>
  14 ldc #8 <String "OK">
  16 invokevirtual #4 <Method void println(java.lang.String)>
  19 getstatic #5 <Field Foo s>
// missing getinstance <Field Foo i>
  22 pop
  23 getstatic #9 <Field byte b>
  26 iconst_1
  27 iadd
  28 i2b
  29 putstatic #9 <Field byte b>
  32 getstatic #2 <Field java.io.PrintStream out>
  35 ldc #3 <String "Oops">
  37 invokevirtual #4 <Method void println(java.lang.String)>
  40 goto 52
  43 astore_1
  44 getstatic #2 <Field java.io.PrintStream out>
  47 ldc #8 <String "OK">
  49 invokevirtual #4 <Method void println(java.lang.String)>
  52 return
Exception table:
   from to target type
     0 7 10 <Class java.lang.NullPointerException>
    19 40 43 <Class java.lang.NullPointerException>
*/

(Review ID: 121132)
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