Can I get an instance of the caller in Java?

Question

There is a library that calls my method with several arguments. I would like to get another argument, but the library does not provide it to the method that it calls.

By decompiling the library, I see that it has an argument and is assigned to the instance variable (not private, but not public). I know that I can get a variable using reflection if I have an instance, but I don't have an instance either.

Is there any way to get an instance? SecurityManager has getClassContext () , but it just gives me an instance class - I want the instance itself.

As a quick example of what I want:

public class A { int b; public A(int b, int c) { this.b = b; D(c); } } public class D { public D(int c) { // Somehow I want to get at the calling instance of A b from here, // and A belongs to a library which I didn't write. } } 

Alternatively ... I know that b used as an argument in callstack. Therefore, if someone knows how I could access b , which was passed to constructor A , that would be acceptable.

If none of them is feasible ... I can decompile A and compile it the way I want, and then I will either need to do some skill in loading classes, or I will have to modify the contents of the jar, None of these sounds is not desirable, so I hope someone knows how to access instance A or argument b from the call stack.

Answer 1

With the code you provided, I could think of writing an aspect that I mean by using aop and trying to use a join point to get the arguments that are passed to the A () constructor

Answer 2

Somehow I want to get from the calling instance A b from here

Short answer: you cannot.

Long answer: you can get it if you either run it on the debugger or your own JVM.

Another solution: use aspect-oriented programming with a framework like AspectJ

Answer 3

You cannot do this. See this post for more details.

There is no such thing as an “owner”, so you cannot get the calling instance unless you explicitly reference the parent:

 class A { int b; A(int b, int c) { this.b = b; new D(this, c); } } class D { D(A a, int c) { ... } } 

It seems that either in accordance with the library you should not receive such an instance, or it is poorly designed.