1 University of Utah – School of Computing Computer Science 1021 "Object-Oriented Programming"

University of Utah – School of Computing University of Utah 2 Procedural Programming What we've done so far: -variables -methods that operate on those variables

University of Utah – School of Computing University of Utah 3 Large-Scale Programming Hard to write BIG programs using procedural programming techniques WHY?

University of Utah – School of Computing University of Utah 4 Problem #1 Global Variables!

University of Utah – School of Computing University of Utah 5 Problem #2 Limits of human comprehension

University of Utah – School of Computing University of Utah 6 Problem #3 Brittle dependencies

University of Utah – School of Computing University of Utah 7 Conceptual Leap 1. Dividing a large job into small methods 2. Dividing several large jobs (or concepts) into multiple classes!

University of Utah – School of Computing University of Utah 8 Analogy Toy blocks

University of Utah – School of Computing University of Utah 9 Classes Have variables and methods Or "attributes" and "behaviors"

University of Utah – School of Computing University of Utah Example Modify our circle drawing program What attributes does a circle have?

University of Utah – School of Computing University of Utah Circle class public class Circle { int x, y; int radius; Color color; }

University of Utah – School of Computing University of Utah Circle class What do you want to do with a circle? -Draw it? -Move it? -Resize it? -Calculate area? -Calculate circumference?

University of Utah – School of Computing University of Utah Methods class Circle { int x, y; int radius; Color circle; void draw(Graphics g) { //do stuff } double computeArea() { //do stuff }

University of Utah – School of Computing University of Utah How to draw a circle? void draw(Graphics g) { }

University of Utah – School of Computing University of Utah How to find the circle's area? double computeArea() { }

University of Utah – School of Computing University of Utah Classes vs. Objects A class is just the "definition" or the code An object is when you make a variable whose type is a class Example: - JPanel p; - p = new JPanel();

University of Utah – School of Computing University of Utah Block example revisited Wrap up all attributes and methods inside a class Easier to manage! Safer too? Why?

University of Utah – School of Computing University of Utah Car example You can drive a car without knowing how it works internally "public" user interface: -steering wheel -gas/brake pedals -ignition

University of Utah – School of Computing University of Utah Car example You can drive a car without knowing how it works internally "private" inner workings -don't know, don't care

University of Utah – School of Computing University of Utah "public" explained public methods and variables -Other classes can use them So far, this is all we've used

University of Utah – School of Computing University of Utah "private" also! private methods and variables -Other classes may NOT access them Used for internal data

University of Utah – School of Computing University of Utah A General Rule private variables -they are our internal data public methods -they are how other classes use our class

University of Utah – School of Computing University of Utah Circle class revisited class Circle { private int x, y; private int radius; private Color circle; public void draw(Graphics g) { //do stuff } public double computeArea() { //do stuff }

University of Utah – School of Computing University of Utah Why public and private? Secrecy? No. Simplicity? Yes. Order? Yes. Maintainability? Yes.

University of Utah – School of Computing University of Utah Examples Math.random() JPanel.add()

University of Utah – School of Computing University of Utah Tomorrow Work on "Circle" example together

University of Utah – School of Computing University of Utah Reminder Homework 5 is due tomorrow, not Wednesday, due to Fourth of July Office hours today from 9:45 to noon

University of Utah – School of Computing University of Utah Request for Comments Please fill out online survey!