Getting an object from its address

Question

This is just for general knowledge and I am pretty sure it may not be possible, but I am curious to know.

Suppose I have a Student class object s1 and I pass it to a function as myFunc(s1.toString()). I haven't overrided toString() function. When the parameter will reach to the function, can I reference back to the original object just by it's address?

code:

public static void main(){
    Student s1;
    myFunc(s1.toString());
}
public static myFunc(String address){
    Student s2;
    s2 = //get s1 object from address string
}

Answer 1

What you are asking to do is impossible by design while staying within the Java language. In contrast to languages like C that simply hand over arbitrary control over a region of memory to a program, the JVM uses a capability model, where both security and some measure of correctness depend on the fact that references can't be forged (manufactured from user-defined data such as a string instead of generated by the VM itself)--the only official way to get a reference to an object is to create that object via new or to copy an existing reference.

Answer 2

While the default hashcode in the common implementations does use the object address to generate it, it's not reversible (and the address being used is an implementation detail, not a specified functionality).

Even if it were possible, the address of an object can change during the runtime (whereas the default hashcode doesn't), so it wouldn't be a viable approach even if there were a way to reverse it.