Question

Java uses pass-by-value, both with Objects and primitive types. Because Java passes the value of the reference, we can change the value of target but cannot change the address.

How does this compare with C++?

Answer 1

The difference is whether you can affect a variable in the calling function.

Let’s leave objects aside for a moment. In Java, which is purely pass-by-value, you can’t change the calling function’s value of a variable passed into a called function. Example:

void foo() {
    int a = 42;
    bar(a);
    System.out.println("foo says: " + a);
}
void bar(int a) {
    a = 67;
    System.out.println("bar says: " + a);
}

If you call foo, you’ll see:

bar says: 67
foo says: 42
bar could not change foo’s a.

That’s true in C++ if you pass by value. However, if you pass by reference, you’re passing a reference to the calling code’s variable. And that means the called code can change it: