Pass-by-value Pass-by-reference

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Many argue that Java is ONLY pass-by-value, but it’s more nuanced than that. Compare the following C++ and Java examples to see the many flavors of pass-by-value (aka copy) and pass-by-reference (aka alias).

C++ Example (complete code)

// passes a COPY of the object
static void passByCopy(PassIt obj) {
   obj.i = 22;  // only a "local" change
}

// passes a pointer
static void passByPointer(PassIt* ptr) {
   ptr->i = 33;
   ptr = 0; // better to use nullptr instead if '0'
}

// passes an alias (aka reference)
static void passByAlias(PassIt& ref) {
   ref.i = 44;
}

// This is an old-school way of doing it.
// Check out std::swap for the best way to do this
static void swap(PassIt** pptr1, PassIt** pptr2) {
   PassIt* tmp = *pptr1;
   *pptr1 = *pptr2;
   *pptr2 = tmp;
}

Java Example (complete code)

// passes a copy of the variable
// NOTE: in java only primitives are pass-by-copy
public static void passByCopy(int copy) {
   copy = 33;  // only a "local" change
}

// No such thing as pointers in Java
/*
public static void passByPointer(PassIt *ptr) {
   ptr->i = 33;
   ptr = 0; // better to use nullptr instead if '0'
}
*/

// passes an alias (aka reference)
public static void passByAlias(PassIt ref) {
   ref.i = 44;
}

// passes aliases (aka references),
// but need to do "manual", potentially expensive copies
public static void swap(PassIt ref1, PassIt ref2) {
   PassIt tmp = new PassIt(ref1);
   ref1.copy(ref2);
   ref2.copy(tmp);
}

Found a mistake? Have a question or improvement idea? Let me know.

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