Remove an interface from a Class

[kevinkilroy]

Hi,

Is it possible to remove an interface from a class?

e.g.

public class SomeClass implements SomeInterface, AnotherInterface

{

}

Thanks in advance!

Kevin.

[megalodon]

How I approached this:

I obtained the list of interface CtClasses using CtClass.getInterfaces();

I removed the Interface I chose from the list of CtClasses. Then I applied the filtered list of interfaces onto the CtClass using CtClass.setInterfaces() and passed in the filtered CtClass Array of Interfaces to that method. Tested this with a simple example.

[kevinkilroy]

Hi,

Could you provide an example please? I'm receiving the following exception:

java.lang.LinkageError: loader (instance of  sun/misc/Launcher$AppClassLoader): attempted  duplicate class definition

With this code:

ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.northwales.ilm.domain.ContextBarItem");
CtClass[] ifs = cc.getInterfaces();
CtClass[] newIfs = new CtClass[1];
newIfs[0] = ifs[0];
cc.setInterfaces(ifs);
cc.writeFile();
Class newClass = cc.toClass();
ContextBarItem cbi = (ContextBarItem)newClass.newInstance();

Thanks!

Kevin.

[megalodon]

Hello,

I do not think there should be anything wrong with the interface-removing part. You can verify this by printing the interface class names before and after you change them, if you need. I can think of 2 possibilities for the exception:

I would put my money on this one:

1. You are trying to modify a class that has already been loaded. This is not allowed by the JVM. You might have seen this thread in a forum that posts your same error: http://lists.jboss.org/pipermail/jboss-user/2009-March/152559.html. You might want to modify your class during load time in this case using a javaagent and classfiletransformer (or some other approach).

2. You might need a different context class loader to load the ContextBarItem class. The default CtClass.toClass() uses the context class loader of the current thread. You could use an overloaded Class:

public java.lang.Class toClass(java.lang.ClassLoader loader,
                               java.security.ProtectionDomain domain)

                        throws CannotCompileException
 
suppose the object of ContextBarItem class is myCBI,

Class newClass = cc.toClass(myCBI.getClass().getClassloader(), myCBI.getClass().getProtectionDomain());

Check out http://www.csg.is.titech.ac.jp/~chiba/javassist/tutorial/tutorial.html#toclass and Javassist API for more details. I'm not too clear on these concepts either.

-Arvind