What is the difference between a pointer and a reference variable in Java?

Question

My Java book explains that to use objects, we can assign them to reference variables. How is that different from a pointer to an object? Does Java have pointers?

Thanks :)

Answer 1

A reference is sort of like a pointer that you can't do arithmetic on... although it's more opaque. While the underlying bits may be an address in virtual memory, they don't have to be. They're just a way of getting to an object (or representing the null value). So while they're not exactly the same, if you're used to thinking of a pointer as "a way of identifying an object or navigating to it" (in some sense) then yes, those thoughts apply to references too.

Java doesn't have pointers as such (unlike, say, C# which has references and pointers - the latter being used in "unsafe" code).

Answer 2

The terms "reference" and "pointer" are basically equivalent. Much of the literature I've seen about the basics of Java claims that Java has no pointers. But if you try to use a null reference you get a NullPointerException. So it's all semantics.

(The real difference is, in C or C++ the term "pointer" strictly means an integer that happens to be the memory address of some data. Whereas in Java the term "reference" more closely matches the C++ "reference" concept. You can't work with the memory address directly even if you want to, but you use it the same way.)