CODEWITHSUNDEEP
javaobject
James Raitsev
James Raitsev

Reputation: 96391

Is it possible to find the address of a non-primitive variable in Java?

If Integer i = 88, what is the memory address i resides at?

Additionally, if as part of Debugger, id number changes, is it indicative of the fact that a new object was created?

enter image description here

Upvotes: 2

Views: 197

Answers (3)

user1134904
user1134904

Reputation: 37

Unless you have some one very close from JVM development team you cannot find out what type of data/address is stored in reference variable :) . All we need is access to the object residing in that reference and manipulate/execute it.

i am not sure about the second part of your question. Also, i cannot confirm if ID (in debugger) refers to java heap memory location.

Upvotes: 0

Russell Zahniser
Russell Zahniser

Reputation: 16364

The answer to your second question is yes, the "id" you see in Eclipse's debugger uniquely identifies an object and so a change in it means a new object was created. So, for example:

Integer i = 55;
Integer j = new Integer(55);
Integer k = Integer.valueOf(55);

Here i and k will have the same id, since they refer to the same object; j will be different.

The memory address of one of these objects is not really a useful piece of information, since objects move around in memory. All you can know is that if i == k, they are the same object. (So here, i == k but i != j).

Upvotes: 2

Tomasz Nurkiewicz
Tomasz Nurkiewicz

Reputation: 340733

Why would you need a memory address of any object in Java? All you can say is that Integer instance lies in heap. You cannot find the exact address.

Second question: yes, Integer objects are immutable, so when the value of a variable of type Integer changes it means it points to a different instance of Integer. However it doesn't necessarily mean a new instance was created. new Integer(42) always creates a new instance while Integer.valueOf(42) will create the same instance every time it is called.

Upvotes: 6

Related Questions