Passing Reference Types

Consider the methods one and two defined in Program . In this case, the variables x and y are reference types. The type of x and y is Obj. Thus, x and y both refer to instances of the Obj class defined on lines 3-13.

  
Program: Parameter passing example: passing reference types.

The semantics of pass-by-value for reference types work like this: The effect of the formal parameter definition is to create a local variable of the specified type in the given method. For example, the method two has a local variable of type Obj called x. When the method is called, the actual parameters are assigned to the formal parameters before the body of the method is executed.

Since x and y are reference types, when we assign y to x, we make them both refer to the same instance of the Obj class. Therefore, the output obtained produced by the method one defined in Program  is:

1
2
2

Copyright © 1998 by Bruno R. Preiss, P.Eng. All rights reserved.