Name: vrR10176 Date: 12/03/2002



JDK1.4.2-b07 (and all previous) throws ClassCircularityError instead
of ClassFormatError if default class loader tries to load interface
which is its own superclass.

The section 4.1 "The ClassFile Structure" of 2nd JVM spec says:
"super_class
...
For an interface, the value of the super_class item must always be a
valid index into the constant_pool table. The constant_pool entry at
that index must be a CONSTANT_Class_info structure representing the
class Object."

Moreover section 5.3.5 of the 2nd JVM spec describes the steps
required to derive a class from a class file representation:

Step1 says that first, the JVM determines whether is has already
recorded that L is an initiating loader of a class or interface
denoted by N. This is not true in this case, so step 1 can be
ignored.

Step 2 says that the JVM attempts to parse the purported
representation. The following errors are detected at this phase:

- ClassFormatError if the bytes violate any of the constraints
   set forth in sections 4.1 or 4.9.1
- UnsupportedVersionError if the version is incorrect
- NoClassDefFoundError if the name of the class is incorrect

ClassCircularityError may be thrown by steps 3 or 4, but only
if Step 2 has completed successfully. For this test case, Step 2
cannot complete successfully, so ClassCircularityError must not be
thrown.

So if interface is its own superclass then class format checker
must throw exactly ClassFormatError.

To reproduce the issue execute following test.
The test tries to load an interface which extends itself.

------------ test.java ------------------------
public class test {
    public static void main(String args[]) {
        try {
            Class.forName("test_interface");
            System.out.println("Error: No exception");
        } catch (Throwable e) {
            System.out.println("Exception: " + e);
}
    }
}

------------ test_interface.jcod --------------
class test_interface {
  0xCAFEBABE;
  0; // minor version
  46; // major version
  [] { // Constant Pool
    ; // first element is empty
    class #2; // #1
    Utf8 "test_interface"; // #2
  } // Constant Pool

  0x0601; // access
  #1;// this_cpx
  #1;// super_cpx

  [] { // Interfaces
  } // Interfaces

  [] { // fields
  } // fields

  [] { // methods
  } // methods

  [] { // Attributes
  } // Attributes
} // end class test_interface

------------ Logs -----------------------------
%javac test.java
%
%jcod test_interface.jcod (see attachments for class files)
%
%java -version
java version "1.4.2-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-beta-b07)
Java HotSpot(TM) Client VM (build 1.4.2-beta-b07, mixed mode)
%
%java -Xfuture test
Exception: java.lang.ClassCircularityError: test_interface

------------------------------------------
ClassFormatError is expected.

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