Lecture 14 Objectives

Lecture 14 Objectives [Nov 16]prev next

MUSICAL COMPOSITION: Carmina Burana, O Fortuna, Carl Off

03:04

At the end of today's class you should

HAVE READ:

[446-467]
Pay attention to the chapter summary [466]

KNOW:

what the protected modifier enables
what the private modifier implies for inheritance
how to access a redefined base method within an overridden method
the difference between overriding and overloading
the java.lang.Object class and its key methods: toString(), hashCode(), equals(Object o)
the instanceof operator
the concept of down-casting an object from a base type to a derived type
Java allows only single inheritance

BE ABLE TO:

design a base class and a set of potential derived classes that extend the base class
use super() within a constructor, and understand how it works
use this() within a constructor, and understand how it works

DAILY QUESTION:

You are given two classes

package p1;

public class Sample {
   public int a;
   protected int b;
   private int c;
   int d;

   public static int e;
   static protected int f;
   static private int g;
   static int h;
}

package p2;

public class DerivedSample extends Sample {

   private void doSomething() {
       // here.
   }

}

Which of these variables (both instance and static) are visible within the doSomething() method?

Sample Exam question(s)

1. A library has a number of items that can be borrowed. The following table describes the situation

Item	Behavior
LibraryItem	Every library item, by default, can be borrowed freely for 14 days. Each item has a name and a UPC code.
VHS Video	Videos cost $1.00 to borrow, and must be returned within 7 days.
DVD Video	DVD videos cost $2.00 to borrow, and must be returned within 7 days. Note that some DVDs come with multiple disks.
Reference	Reference materials, such as Encyclopedias and Dictionaries, cannot leave the library and can only be borrowed freely for 2 hours at a time.
Magazines	Magazines cannot leave the library, but they can be borrowed freely for up to 8 hours
NYTimes BestSeller	NYTimes Best Seller books can be borrowed freely, but must be returned within 3 days

Design a set of classes that captures the relationships between the base class LibraryItem and its five derived classes.

2. You are given a base class B, a derived class C, and a method m of the derived class C.

2a) You are told that method m is an overloaded method. Explain what this means in relation to either class B or C.
2b) You are told that method m overrides another method n. Explain what this means in relation to either class B or C.

3. You are asked to design a class representing a Rectangle. You are given a Point class that represents int x and y values in the plane. Design the constructors for the Rectangle class so that you can:

    3a) Create a rectangle given two points (an upper left corner and a lower right corner)
    3b) Create a rectangle given four int values (x1,y1, x2,y2)
    3c) Create a degenerate rectangle given just a point (thus it is both upper left and lower right)
    3d) Create the default rectangle whose coordinates represent the (0,0,0,0) rectangle

make sure you use the this() construct, with suitable arguments, when designing these constructors.