!7

set flag AllPublic.

lib 1400554 // javassist

import javassist.CtClass;

import javassist.CtClassType;

import javassist.bytecode.*;

p {

  ClassFile cf = new ClassFile(false, "User123", null);

  cf.setInterfaces(new S[] { className(IF1) });

  var cp = cf.getConstPool();

  // add default constructor

  MethodInfo mi = new MethodInfo(cp, "<init>",

    Descriptor.ofConstructor(new CtClass[0]));

  var code = new Bytecode(cp, 1, 0);

  CtClass ctSuperclass = new CtClassType("java/lang/Object", cp);

  code.addInvokespecial(ctSuperclass, "<init>",

    Descriptor.ofConstructor(new CtClass[0]));

  code.addReturn(null);

  code.setMaxLocals(1);

  mi.setCodeAttribute(code.toCodeAttribute());

  cf.addMethod(mi);

  byte[] bytes = bytesFromDataOutputStream(stream -> cf.write(stream));

  var cl = new InMemoryClassLoader(myClassLoader());

  Class<? extends IF1> c = cast cl.defineAClass("User123", bytes);

  print(c);

  IF1 f = newInstance(c);

  print(f);

}