Java Language C++ Comparison Pass-by-value & Pass-by-reference
Example
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);
}
