CS21 Week10 In-Class Exercises

% cd  
% cd cs21
% mkdir week10
% cd week10
% pwd 
% cp ~newhall/public/cs21/week10/* .   

1. Start by examining the Top, Middle, and Bottom classes. Then open TryInheritance.java, take a look at what it is doing and compile and run the code.

   class hierarchy:
   
              Top
           ---------------
           | Data:    t
           | Methods: getT
           ---------------
                |
              Middle
           ---------------
           | Data:    m            Middle inherits t and getT
           | Methods: getM
           ---------------
                |
              Bottom
           ---------------
           | Data:    b            Bottom inherits t and m, getM and getT
           | Methods: getB
           ---------------
   
   This example illustrates some important features of inheritance in Java:
   
     1. When you create an instance of class, Java automatically invokes
        the constructor of the parent class first to initialize its part
        of the object
   
     2. If a constructor does not initialize the data members of a class,
        Java will automatically initialize them to default values, which
        are: zero for numbers, false for booleans, and null for Objects
        such as Strings.
   
     3. You can use the "instanceof" operator to determine if a given
        object is an instance of a particular class.
   
   Let's add constructors that take params to Middle and Bottom, and then
   construct a new Bottom object by using invoking the non-default constructors
        

2. Open the Person, Faculty, Student2, TenureTrack, Visiting, and DeptChair dot java files. These are classes that are related by the following class heirarchy:

             Person		all classes implement Comparable<Person>
            /     \		(inherited from the Person class)
           /       \
       Student2    Faculty
                  /       \
                 /         \
            TenureTrack   Visiting
                /
               /
           DeptChair
    
        

   Notice that the toString method is overridden in the derived classes. See how super is used to get a String representation of the private data members that are inherited by the derived classes. Also, note that each class implements the Comparable interface, and that all the derived classes do not override the Person class's compareTo method.

         (a) examine RunStudentFaculty.java file.  Notice how a Person object
             reference can refer to a Person, or a Student2, or a Faculty, or a ...
             object.  Compile and run the program.
         (b) to the Visiting class, change the toString method to return 
             a string of the form:
                        name
                        age
                        Visiting Professor
                        department
                        start date - current date
             then re-compile and run
        

3. Next, follow the TODO items in the RunStudentFaculty.java file. Do one at a time, compiling and testing as you go. Here you will create arrays of objects in this class heirarchy, and write generic methods to print the array contents and sort the array contents (i.e. a single Sort method should work for an array of Person, or an array of Visitor, or and array of TenureTrack, ...).

Object class

Comparable Interface