To use a class, you have to create instances of the class, which are called objects. In Ultra Fractal, you always use a reference to the object. Such an object reference can be stored in a variable with the class name as type.

Let’s create some objects using the example Point class given in Classes:

  ; Declare a new object variable  Point p  ; Create a new Point object and store it in p.  p = new Point(3, 4)  float d = p.distance(new Point(0, 0))  ; Returns 5    

The new operator takes the name of the class as a function, together with the arguments for the constructor. It creates a new instance of the Point class and returns a reference to it.

When you copy an object variable, you only copy the reference to the object, not the object itself. Copying an object variable therefore does not create a new object. Example:

  Point pt1 = new Point(3, 4)  Point pt2 = pt1 ; This copies a reference!  pt2.x = 10      ; Now pt1.x is also 10  print(pt1.x)    ; This will print 10  pt2 = new Point(pt1.x, pt1.y) ; Creates a true copy  pt2.x = 6       ; Only modifies the copy  print(pt1.x)    ; This still prints 10  print(pt2.x)    ; This prints 6    

You can also set an object variable to the special value 0, the null reference. This clears the reference, so it points to no object at all. This is often useful when programming, for example when building a linked list. You can test if an object value is empty by comparing with 0, or by treating it as a boolean expression:

  Point p = 0  if p != 0    ; This will not be executed.  endif  if p    ; Will not be executed, same as above.  endif  int x = p.x  ; Compiles, but illegal!  if p    x = p.x    ; This is safe  endif    

When an object reference can be null, as in the example above, you need to test it first. Only use the object reference if it is non-null. If you access a field or method using a null object reference, Ultra Fractal will generate a run-time error and halt execution of the current calculation.

Next: Member visibility

See Also
Memory management