Question

Lets say this is the C++ code:

void change(int& x){
    x++;
}

or

void change2(int* a){
    *a++;
}

Both will change the global x, right?

So how can I do something like that in java?
Specifically, I want to point to a Vector object

But since Java has no pointers, I’m not sure what to do.
From searching the internet I saw people saying that Java does that in some other way, but I haven’t found any real example.

Thanks for
help!

Answer 1

In Java, instead of pointers you have references to objects. You cannot pass a primitive type by reference, but you can wrap a primitive type inside an object and then pass a reference to that object.

Java provides the type Integer which wraps int, however this type is immutable so you cannot change its value after construction. You could however use MutableInt from Apache Commons:

void change(MutableInt x) {
    x.increment();
}

The change to x will be visible to the caller.

---

Specifically, I want to point to a Vector object

When you write Vector v = ...; you are assigning a reference to a vector to the variable v. A reference in Java is very similar to a pointer. References are in fact implemented internally using pointers.

Java uses pass by value. When you pass a vector to a method, you are actually copying a reference to that vector. It does not clone the vector itself. So passing a reference in Java is very similar to passing a pointer in C++.