Module 2, part 2. More on OO
Introduction
We discuss a bunch of ideas in OO in Java.
Contents
| No. | Topic | Discussion |
|---|---|---|
| 1. | Static components, (blecture doc ppt.pdf) Reading: Gries/Gries, Sec. 3.3, pp. 122–124. |
Only one copy of a static variable or method exists, and it resides in the class file drawer. |
| 2. | The bottom-up rule, also called the method-overriding rule. (html) |
The bottom-up rule describes how to find a variable, or a method with a certain signature, in an object. Because of the way we draw objects, use of this rule always finds the overriding method, if a method is inherited. |
| 3. | The inside-out rule, (blecture doc ppt.pdf) |
Within a construct one can reference variables and methods declared in that construct and in surrounding constructs. |
| Reading for items 2 and 3. |
Gries/Gries, Sec. 4.1.1, pp. 143–144; Sec. 3.1.2, pp. 109–110. | |
| 4. | The class invariant. (blecture doc ppt.pdf) Reading: Gries/Gries, Sec. 4.1.2, pp. 146–147. |
The set of constraints given in the documentation of the fields of a class constitute the class invariant. We show why you should be careful in writing and using it. |
| 5. | Calling constructors from constructors. (blecture doc ppt.pdf) |
Within a constructor, one can call a constructor in the same class or in the superclass. Such a call must be the first statement of the constructor body. |
| 6. | The default constructor. (blecture doc) |
If you don't declare a constructor in a class C, Java declares one for you. It looks like this: public C() {super();} . |
| Reading for items 5 and 6. |
Gries/Gries, Sec. 3.1.3, pp. 110–112; Sec. 4.1.3, pp. 147–148. | |
| 7. | Casting about. Watch the Widening and Narrowing lectures on p. 4-3 of the ProgramLive CD. | We extend the notion of narrower and wider types to class types and show the consequences thereof. We also introduce operator instanceof. |
| 8. | Apparent and real classes. (blecture doc ppt.pdf) |
The apparent class of a variable is a syntactic property; its real class is a semantic property. We show how each is used. |
| Reading for items 7 and 8. |
Gries/Gries, Sec. 4.2, pp. 148–153. | |
| 9. | Function equals. (blecture doc ppt.pdf) Reading: Gries/Gries, Sec. 4.3.2, pp. 154–155. |
Function equals is defined in class Object, the superest class of them all. So it is inherited by all classes. We show you the convention for overriding it in a subclass. |
| 10. | Object-oriented design. Lesson page 3-8 of ProgramLive contains
general discussion of OO design with classes and an extensive example. Lesson page 4-4 extends this to a discussion of the use of subclasses and gives an extensive example. Reading: Gries/Gries, Sec. 4.5, pp. 156–161. |
We make a first attempt at discussing how to organize a program
into classes and subclasses. This is only an introduction
to the topic. Generally, nouns of the problem domain become classes, while verbs
become method names.
Make B a subclass of C if "B is a C". Example: A dog is an
animal, so make Dog a subclass of Animal.
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