garbage collection - In java, how can we destruct an instance of a class from a method within the class

NOTE: What you suggest is highly unlikely to be useful.

What you can do is use delegation.

class A {
   private AImpl impl = new AImpl();
   public void close() {
      if (impl != null)
         impl.close();
      impl = null;
   }
}

As all references are indirect, you can ensure there is only one reference to the real object and clear it.

---

Proxies in some OSGi containers do this when a component is unloaded. As the container has little control over the lifecycle of the references, it would make it difficult to ever unload a library (the implementation).