SWE 619 In Class Exercise Number 3B

Consider the code:

public class Membership {
    // Membership is a mutable record of organization membership
    // AF: Collect the list as a set
    // rep-inv1: members != null
    // rep-inv2: members != null && no duplicates in members
    // for simplicity, assume null can be a member...

    List<Person> members;   // the representation

    //  Post: person becomes a member
    public void join (Person person) { members.add   (person);}

    //  Post: person is no longer a member
    public void leave(Person person) { members.remove(person);}

• Does join() maintain rep-inv?
• Does join() satisfy contract?
• Does leave() maintain rep-inv?
• Does leave() satisfy contract?


1. Analyze these 4 questions for rep-inv 1.
   
   
2. Repeat for rep-inv 2.
   
   
3. Recode join() to make the verification go through. Which rep-invariant do you use?
   
   
4. Recode leave() to make the verification go through. Which rep-invariant do you use?