!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);
}

Began life as a copy of #1034295