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java and pointers

Started by CProgrammer Apr 30, 2004 at 3:34 AM 5 replies 500+ views

Original Post

113

Apr 30, 2004 at 3:34 AM

I know java doesnt support using pointers. Now my question is how should I do the following without pointers? In C++ i''d always have different classes handling different graphics drawing things. Each oth these classes has a pointer to a ''drawing class''. That way the ''drawing class'' was defined only once but could be used everywhere. How should I do this in java? I cant have a copy in each class, thats overkill. Do you guys suggest passing the value in with every call and retrieving it again after working with the class? Or what? -CProgrammer

johnnyBravo

141

johnnyBravo

Apr 30, 2004 at 3:51 AM

lol its the complete opposite, java doesnt have non pointers.

George2

Apr 30, 2004 at 3:53 AM


 Foo a = new Foo();
Foo b = a;

a doesn''t get copied here , b just points to the same instance of Foo which a points to. Java has pointers but they are hidden. So with your problem just new your Drawing class once, and in each object which needs to draw something store a ''pointer'' to it.

CProgrammer

Author

113

CProgrammer

Apr 30, 2004 at 4:19 AM

Ah thanks guys. Seems my design still works. Although I like the Singleton approach. Thanks. I may use that instead.
-CProgrammer

Clu

May 2, 2004 at 6:02 PM

quote:
Original post by johnnyBravo
lol its the complete opposite, java doesnt have non pointers.

Actually, it does. There are two types of objects (forgive my use of this very overloaded term): reference types and value types. All primitive types (int, boolean, float, byte, short, etc), are value types. This means that every time you pass an instance of a primite type around (through a function, for example), its value is copied. All other types, including all of the base Java library classes as well as all user-defined classes, are reference types. You allocate objects of these types with the "new" operator, and from that point on, you''re dealing with a reference to that object. The dot operator (.) performs a dereference; this is one place where Java and C++ differ. In C++, the dot operator is simply a member access operation, and you use the arrow operator (->) to actually do a pointer dereference.

etothex

May 2, 2004 at 7:17 PM

quote:
Original post by Clu
quote:
Original post by johnnyBravo
lol its the complete opposite, java doesnt have non pointers.

Actually, it does. There are two types of objects (forgive my use of this very overloaded term): reference types and value types. All primitive types (int, boolean, float, byte, short, etc), are value types. This means that every time you pass an instance of a primite type around (through a function, for example), its value is copied. All other types, including all of the base Java library classes as well as all user-defined classes, are reference types. You allocate objects of these types with the "new" operator, and from that point on, you''re dealing with a reference to that object. The dot operator (.) performs a dereference; this is one place where Java and C++ differ. In C++, the dot operator is simply a member access operation, and you use the arrow operator (->) to actually do a pointer dereference.

Actually, they''re not reference types, they *are* pointers...

Just think of ''Object a'' as ''Object* a'' and ''.'' as ''->'' in c++, and you''ll be ok.

(they''re not reference types because otherwise you could do a stl -style swap() function in java)

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