Can an attribute object reach the object for which it is an attribute?

Question

I'm sorry this question might be odd, but some time ago I used python's introspection, and I was wondering if something like that might be available in Java 1.8.

So let's say I have an object a from class A in a situation like this

class A{ B b; }
class B{ public void f(){} }

My question is "can f() know about a?"

Clearly, it can, if I add a backward link, something like:

class A {
    B b;  
    public A() { b = new B(this); } 
}

class B {
    A father; 
    public B(A a){ this.father = a; } 
    public void f(){} 
}

But my question is, in the general setting, without the back like to father or so, is there any introspection mechanic that could allow f() to know about a?

Answer 1

You wish to access the arguments of a function upper in the call stack. In vanilla Java you can't accomplish that, however you can use some AOP framework, which could maintain a shadow stack, so you can introspect it.

Or you might use inner classes. Inner classes contain a hidden field to the instance of the outer class. It can be accessed with the syntax OuterClass.this.

class A{
  public class B{ 
    public void f() {
      System.out.println(A.this.aField);
    }    
  }
  String aField;
  B b = new B(); // Passes a hidden `this` parameter
}