Java反射：在初始化期间设置超类字段

Question

I make initialization a of a new class by reflection and I set one superclass field with 'this':

JavaTask jt = (JavaTask) clazz.newInstance();
for(Field f : clazz.getSuperclass().asSubclass(JavaTask.class).getDeclaredFields()) {
    if(f.getType().equals(JavaTaskListener.class)) {
        logger.trace("Set ReadyListener");
        f.setAccessible(true);
        f.set(jt, this);
    }
}

In such a solution I can access 'this' from a new instance jt after completion of initialization. Would it be possible to somehow set jt after creation of superclass and before creation of base class that I could access 'this' during initialization (without adding non default construction)?

public class LocalMotions extends JavaTask {
   ...
  private int nb = super.jtListener.getParameter(NUMBER));
   ...

Answer 1

Publishing a reference to an object before it is fully constructed is dangerous for the JVM, and strongly discouraged.

When JSR-133 was in the works, and the java memory model was clarified it was stated that the JVM makes no thread safety guarantees for references to an object that is leaked out during construction. That is, it becomes possible for references to leak between threads that have been allocated but not zeroed out etc.

For more details, research JSR 133, the Java Memory Model and 'safe construction techniques'. http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#finalRight is a good starting point.