Sundararajan's Weblog

  • Java
    August 31, 2006

Extra bytes at the end of a .class file?

Guest Author
I accidentally deleted my Jython installation. I attempted to reinstall Jython 2.1). Last time I had installed it with JDK 1.5.0_06. This time I attempted with JDK 6. I got the following error:

D:\\downloads\\Java\\Jython>d:\\jdk1.6.0\\bin\\java jython_21
Exception in thread "main" java.lang.ClassFormatError: Extra bytes at the end of class file jython_21
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)

Looks like Jython folks are self-extracing using the installer (jython_21.class). The installer class has extra bytes at the end of the .class file (which persumably has the installation data in compressed form).

JVM spec second edition section 4.9.1 makes it clear - a .class files can not have extra bytes at the end. May be the .class is verified with JDK 6 - but not with JDK 1.5.0_06? In fact, when using this command

D:\\jdk1.5.0_06\\bin\\java -Xverify:all jython_21

I got the same aforementioned error - so clearly, with bytecode verification 1.5.0_06 also throws the same error. I tried the following command line:

D:\\jdk1.6.0\\bin\\java -Xverify:none jython_21

Guess what? I got the same error! So, it appears that JDK 6's does not allow extra bytes at the end of .class files even when not doing bytecode verification!

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