CS 141 Topics

CS141: Topics for Week 3: Sept 11,13,& 15 2017

Computer Science Headlines: ACM Tech News

Reading:

We will spend 2 weeks on this material.

Complete Chap 2: Using Objects
Chap 3: Implementing Classes

Lab and Other Activities

Lab 3: Classes and Objects

In Class Practice

Methods: Practice problems (pdf).
Classes: Practice problems (pdf).
Scope: Practice problems (pdf).
Pass by Value vs Reference example (pdf).

Practice with references. For the following code, what is printed? Draw what is happening in memory at each step.:

Rectangle rec1 = new Rectangle(5,6,10,10);
System.out.println("rec1: " + rec1);
Rectangle rec2 = rec1;
rec1.setLocation(100,150);
System.out.println("rec1: " + rec1);
System.out.println("rec2: " + rec2);
rec1 =  new Rectangle(50,60,20,20);
System.out.println("rec1: " + rec1);
System.out.println("rec2: " + rec2);

Lecture Discussion Topics:

What are classes? What are objects?

Primitives vs objects, Object references

Existing classes: Java libraries, packages, understanding the Application Programmer Interface (API)

Creating an object using the keyword new and a constructor
The null keyword and Null Pointer Exceptions
Sending an object a message using the public interface. (calling a method)

Motivation of Classes and Objects: Organizing and structuring code to promote reusability, readability, and correctness

Encapsulation: Separating the public interface from the private (hidden) implementation.

Variable scope - what is it and why we have it. Local vs instance/member variables

Class vs Object Analogies: script vs actor, cookie recipe vs the cookie itself

Example: Die class

Components of a Class (also see class template):
- Data (Attributes, Fields):
  - Member (instance) variables (one for each object)
  - Class (static) variables (one for all objects)
- Actions:
  - Public interface (public methods)
    - Common for most classes:
      - Creation: Constructor
      - Access to data: Mutators and Accessors (also called getters and setters)
      - Handy Utility: toString
    - Public methods for a specific class (e.g. In the Die class, one might have a roll() method)
  - Private Implementation:
    - Data hiding: data is usually private. Use accessors & mutators instead.
    - private methods - not accesible from outside of the class.
Testing your code. Unit testing. Tracing your code.
Self referencing using the keyword this
Class design and UML Diagrams
(time permitting) Graphical User Interfaces (GUI) - creating frames, buttons, textfields extends, paintComponent

Object-oriented programming & Class Structure
  ... Class (user defined type)
  ... Object (instance of class)
  ... primitive type vs class type
  ... Attributes, Fields, or Member variables (data)
  ... Methods (actions)

Method Structure:
  ... access specifier or modifier (e.g. public, private)
  ... method name
  ... method parameters
  ... pass by value vs pass by reference
  ... return type, return value
  ... variable scope: local vs global, shadowing

Class Structure (more detail):
  ... Constructors, default constructor
  ... Public interface
  ... Private implementation, data hiding
  ... Mutator methods (setter)
  ... Accessor methods (getter)
  ... toString method
Object Creation and Use
  ... The keyword: new
  ... Sending a message, calling a method
  ... dot notation
  ... (formal) parameter vs argument (actual parameter)
  ... parameter passing
  ... Null pointer and the Null Pointer Exceptions
  ... Self reference keyword this

Code Design and Development
  ... UML Diagram
  ... Javadoc
  ... API (Application Programmer Interface)
  ... Encapsulation, modularization
  ... stepwise refinement
  ... reusability

Testing and Debugging
  ... debugging & testing
  ... tracing code
  ... unit testing

CS141: Topics for Week 3: Sept 11,13,& 15 2017

Computer Science Headlines: ACM Tech News

Reading:

Lab and Other Activities

Lecture Discussion Topics:

Concepts and Vocabulary