🔒 Locked

Simple C++ vs. Java question - public data members

Started by UserX03 Jun 14, 2002 at 12:24 AM 6 replies 400+ views

Original Post

Jun 14, 2002 at 12:24 AM

Here is a simple C++ vs. Java question. In Java, why is it that two different classes can access each others'' public data members (without creating a class object), whereas in (Visual) C++, you get a compile error? I seem to recall that doing this in C++ is allowed just as it is in Java, but obviously the compile error says otherwise. for example in Java, this is allowed: class MyClassA { public int variableA = 1; ... } class MyClassB { ... void function() { int variableB = MyClassA.variableA; } } but in C++, this isn''t allowed ("illegal use of this type as an expression"): class MyClassA { public: int variableA; ... } class MyClassB { public: int variableB; ... } void MyClassB::function() { variableB = MyClassA.variableA; }

Null and Void

163

Null and Void

Jun 14, 2002 at 12:36 AM

Replace MyClassA.variableA with AnInstanceOfMyClassA.variableA.

IndirectX

Jun 14, 2002 at 1:05 AM

That would be allowed if you make those variables static.

Null and Void

163

Null and Void

Jun 14, 2002 at 1:17 AM

quote:
Original post by IndirectX
That would be allowed if you make those variables static.

No it wouldn''t. That would be MyClassA::variableA.

Ziphnor

Jun 14, 2002 at 4:26 AM

quote:
In Java, why is it that two different classes can access each others'' public data members (without creating a class object),

You cant do that in java(at least not without creating an instance of MyClassA and accessing that), not unless the public data member happens to be static too, and in that case you can do it in C++ too.(with the syntax CLASSNAME::STATICDATAMEMBER).

CaptainJester

101

CaptainJester

Jun 14, 2002 at 7:04 AM

quote:
Original post by Ziphnor
You cant do that in java(at least not without creating an instance of MyClassA and accessing that), not unless the public data member happens to be static too, and in that case you can do it in C++ too.(with the syntax CLASSNAME::STATICDATAMEMBER).

You are correct, but in Java static data members are accessed using dot notation, not scope notation. That is where the confusion lies.

---
Make it work.
Make it fast.

"Commmmpuuuuterrrr.." --Scotty Star Trek IV:The Voyage Home

jjmontes

Jun 14, 2002 at 7:09 AM

In Java this is correct:

ClassA.StaticMethod ();
ClassA.StaticVariable ();

If they are static members. In C++ this is done with:

ClassA::StaticMethod();
ClassA::StaticVariable();

And of course, if you have an instance of the class you can access its members as usual.

Real programers are not afraid from maths! (but I am)
JJpRiVaTe (Private Zone)

Grib

Jun 14, 2002 at 11:54 PM

In C++ you could do this:


class myA {
public:
  int varA;
  myA() : varA(1) {}
};

class myB {
  int varB;
  myB() : varB(myA().varA) {}
};

It''s kind of ugly and requires a temporary, it also does not document the dependence that myB has on myA anywhere in myA. I think a protected/private const static int in myA and making myB a friend would be the better way to go.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.