Name: akC45999 Date: 09/28/98



Section 5.3.1 Loading Using the Default Class Loader

of the JVMS reads:

First, the Java virtual machine determines whether a class or interface
named N has been loaded by the default class loader. If so, this class
is C, and no class creation is necessary.

However, the default classloader can load a valid class twice if

a) it was first asked to load an invalid class and
b) the garbage collector has been run

To reproduce compile following 2 source files and run
 java -verbose defaultLoader00102

The tail of the trace shows that the class defaultLoader00102
was loaded twice:

...
[Loaded defaultLoader00102]
initializing class defaultLoader00102
[Loaded BadInterface]
[Loaded java.lang.ClassCircularityError from java/lang/ClassCircularityError.class]
Throwable:java.lang.ClassCircularityError: BadInterface
[Loaded clss2]
[Loaded defaultLoader00102]
initializing class defaultLoader00102
check 3: str 1=modified string
str 2=initial string
failed

Note also, if at least one of calls to check(1,out) or check(2,out)
is not commented, then the test passes.

The bug is discovered when using JDK 1.2fcsI ... 1.2fcsL.

// -------------------------- BadInterface.jasm
public interface BadInterface extends BadInterface {}
// -------------------------- end BadInterface.jasm

// -------------------------- defaultLoader00102.java
import java.io.PrintStream;


class clss2 {

  public static String getStr() {
return defaultLoader00102.str;
  }

}


public class defaultLoader00102 {

  static String str="initial string";
  static {
System.out.println("initializing class defaultLoader00102");
  }

  static boolean check(int n, PrintStream out) {
String str2=clss2.getStr();
out.print("check "+n+": ");
if (str2!=defaultLoader00102.str) {
out.println("str 1=" + defaultLoader00102.str);
out.println("str 2=" + str2);
out.println("failed");
return true;
}
out.println("passed");
return false;
  }

  public static int run(String argv[], PrintStream out) {
    str="modified string";
// if (check(1, out)) return 2;
try {
Class.forName("BadInterface");
} catch (Throwable e) {
out.println("Throwable:" + e);
}
// if (check(2, out)) return 2;
Runtime.getRuntime().gc();
if (check(3, out)) return 2;
return 0;
  }

  public static void main(String args[]) {
System.exit(run(args, System.out) + 95/*STATUS_TEMP*/);
  }
}


// -------------------------- end defaultLoader00102.java

======================================================================

Name: akC45999 Date: 09/28/98


The bug was introduced in JDK 1.2fcsD. JDK 1.2fcsC passes the test.

======================================================================