1. Introduction to Computer Programming
CS 126
Lecture 6
Zeke Maier

2. Plan for Today Questions Administrivia Quiz Instance Variables
Conditionals
Assignment

3. Questions Boolean backed by 1/0? 3 == true (syntax error) Windows 7…
Recovery.gov
Microsoft job cuts

4. Administrivia http://students.cec.wustl.edu/~ejm3/
Lab assignment due Wednesday

5. Method Example Code
Pay attention to the coding style!

6. Variables Def: A symbol which can hold a value of a particular type
<dataType> <name>; int count;
Variable
Instance Variable
Defined within a method
Defined within a class
Can only be accessed within its method
Can be accessed anywhere in the class
Used as a temporary holder of intermediate values
Used to hold values describing the class
A symbol which can hold a value of a particular type

7. Instance/Data Variables
How do we create an instance variable?
<dataType> <name>; int count;
Which variable is the instance variable?
class Student {
String name;
public static void main(String args[]) { }
void printName() {
String fullName = “Mr./Ms. ” + name;
System.out.println(“Name: ” + name);
AKA attributes

8. Class Layout A Class is a blueprint for an object Class consists of:
It models something
Class consists of:
Instance/Data Variables
Describe
Methods
Perform Actions
1 class to model a user, many users
Usually, a class represents a person, place, or thing - it is an abstraction of a concept within a computer program. Fundamentally, it encapsulates the state and behavior of that which it conceptually represents. It encapsulates state through data placeholders called member variables; it encapsulates behavior through reusable code called methods.
Instance variables: noun
Methods: verbs
Let’s sketch out a car class

9. Instance Example Code

10. Conditional Statements
Allows us to change the behavior of the program based on certain conditions
Example: absolute value
If (condition) {
//Statements to execute if the condition is true }
How would we write a method to calculate the abs value for us
Now let’s shorten it:
double abs(double x) {
if (x >= 0)
return x;
return -x; }
How about even vs. odd method
else {
//Statements to execute if the condition is false }

11. Assignment Lab 1 due Wednesday in Lab Readings Wednesday
AD Chapter 4:
KG Notes