Exercise: Applying "Contract Design Scheme (view this) " for handling Exceptions

Not collected

Recall the discussion of the STACK data structure where

two functions defined for a stack:


  • top() returns a reference to the topmost element on the stack

the element itself is unaffected by the operation

the element remains on the stack
    


  • size() returns the number of elements currently on the stack




Assume these implementation details about a stack:


       the stack is implemented using an array called elements

       

       topIndex is the index of the topmost element on the stack









The following is one possible implementation of the operation top:

Object top() throws EmptyException

{

    if (size() > 0)

        return elements[topIndex];

    else

        throw(new EmptyException());

}



Part 1: Identify the contract implicitly defined by this method

That is: Specify its precondition and postcondition



Part 2: Try to suggest another contract

How is this new contract different from the first one?
A
© Lynne Grewe