1. CS Week 2
Jim Williams, PhD

2. Society of Women Engineers
"Not just for women and not just for engineers; all students are welcome. We are especially looking for more computer science students!" - Emile Wille (Marketing Officer for SWE)

3. This Week Team Lab: Tuesday or Wednesday Program 1: Due Thursday
Lecture: Primitive Data Types and Expressions

4. Team Labs First meeting this week. 1350 cs and 1370 cs Meet TAs & LAs
1st floor, around corner from elevators
Meet TAs & LAs
Work in small groups and pairs
Discuss Terms, Trace & Explain code
Edit-Compile-Run Cycle on the command-line

5. Pair Programming 2 people working together on 1 computer.
One person types, the other provides direction and reviews.
Many report more confidence in solution and more enjoyment programming.
Important to switch roles (who has the keyboard).
Provide respectful, honest and friendly feedback.

6. Learning to Trace with Java Visualizer
Java Visualizer available via our course website or:
import java.util.Scanner;
public class RectangleArea {
public static void main(String [] args) {
Scanner input = new Scanner(System.in);
int height = 0;
int width = 0;
System.out.print("Enter height: ");
height = input.nextInt();
System.out.print("Enter width: ");
width = input.nextInt();
int area = height * width;
System.out.println("A rectangle with height " + height
+ " and width " + width + " has an area of: " + area);
input.close();
return; //optional at end of method, unless returning value }

7. Programming Process Users Files Programmer Editor (Virtual) Compiler
Machine
Compiler
Hello.java
Hello.class
Computer
Files
Programmer

8. Programming Errors Naming/Saving Syntax/Compile time Runtime & Logic
Editor
(Virtual)
Machine
Compiler
Hello.java
Hello.class
Computer
Files
Programmer

9. Edit-Compile-Run Cycle
From the command-line:
notepad
javac
java

10. Programming Process Question
Cat.txt
Cat.java
Cat.class
Cat
For the class named Cat, what is the name of the file that the compiler creates and is provided to the Java Virtual Machine to run?

11. Learning Programming Lots of little steps that quickly build
Not mastering little steps creates bigger steps
Goes beyond Remembering and Understanding to Applying, Analyzing, Evaluating and Creating.
Goal: Have basic fluency in Java and be able to solve small problems using it.

12. Primitive Data Types int whole numbers (4 bytes)
double floating point numbers (8 bytes)
char single character (2 bytes)
boolean true or false value (>= 1 bit)
less commonly used:
float (4), long (8), short (2), byte (1)

13. Primitive Data Type Conversion
Which work?
double a = 5;
double b = 6.0;
int c = 3.0F;
float d = b;
c = d;
d = c;
char e = 'A';
int f = e;
short s = f;
int h = / 3;
int i = 10.0 / 3;
int j = (int) 10.0 / 3;
double k = (int) 10.0 / 3.0

14. Operator Precedence & Associativity

15. Constant public class World { public static void main(String []args) {
int size = 3;
final int MAX_SIZE = 10; }

16. String class A reference (class), not a primitive data type.
Frequently used
final String TITLE_PREFIX = "Welcome to ";
int week = 2;
String welcome = "Week " + week;
System.out.println( TITLE_PREFIX + welcome);

17. What are the values in a, b & c?
int a = 5;
int b = 7;
int c = a;
b = c;
a = b;

18. What are the values in a, b & c?
int a = 2;
int b = 1;
int c = a + b;
a = b;
a = c;

19. Swap values in a & b int a = 5, b = 3;
Write code to swap values in a & b.
a = b;
b = a;
c = b;
b = c;
c = a;
a = c;
Google "swapping values without third variable" for many creative ways.

20. Application: Temperature Conversion
(Degrees Fahrenheit – 32) x 5 / 9 = Degrees Celsius
What symbols have different meanings in Java?
What changes must be made to implement this
equation in Java?
Retrieval practice
importance of committing to an answer

21. My List X vs * equals (==) vs assignment (=)
value is stored on the left hand side of assignment (=) operator
Variables:
name areas of computer memory, declare before use, declare type of data, initialize
Variable names:
start with letter, include letters numbers and _, but no spaces
Conventions:
camelCasing, spell out names
Semicolon at the end of statements

22. CS Core Principles:
Algorithms: A step-by-step set of operations to be performed.
Analogy: Recipe, Instructions
Abstraction: a technique for managing complexity.
Analogy: Automobile, CS200 Computer View

23. Methods
Lots of existing code that you can use rather than writing yourself.
To use, "call the method".
The method executes (runs) and may return a value.

24. Calling Class (static) Methods
double numInts = Math.pow( 2, 32);
double root = Math.sqrt( 16);
int num1 = 16;
int num2 = 3;
double result;
result = num2 + Math.sqrt( num1);

25. Defining Methods public class M { //method definition
static void mPrint() {
System.out.println("my print"); }
public static void main(String []args) {
M.mPrint(); // method call.
B is the correct answer

26. mPrint - which is Call, Definition?
mPrint call
then
mPrint definition
static void mPrint() {
System.out.println("my print"); }
public static void main(String []args) {
mPrint();
B is the correct answer

27. Argument vs. Parameter static void printCount(int count) {
public static void main(String []args) {
int num = 10;
printCount( 23);
printCount( num+3); }
static void printCount(int count) {
System.out.println( count);
count is a parameter (zyBooks) or formal parameter
the number 23, for example is an argument (also called an actual parameter).

28. Is count: Argument or Parameter?
public static void main(String []args) {
int num = 10;
printCount( 23);
printCount( num+3); }
static void printCount(int count) {
System.out.println( count);
argument
parameter
count is a parameter (zyBooks) or formal parameter
the number 23, for example is an argument (also called an actual parameter).

29. Returning a Value from a Method
static int triple(int num) {
return num * 3; }
public static void main(String []args) {
int value = 5;
int result = triple( value);

30. Which is called first: calc or println?
error
static int calc(int num) {
num -= 33;
return num; }
public static void main(String []args) {
int n = 55;
System.out.println( calc( n));
put a print statement within the calc method to see if it is called before the println method.

31. What prints out? static void calc(int num) { num = 3; }5 35
error
static void calc(int num) {
num = 3; }
public static void main(String []args) {
int n = 5;
calc( n);
System.out.println( n);
try it.

32. Return to Converter
double degreesCelsius; double degreesFahrenheit = 100.0;
degreesCelsius = (degreesFahrenheit ) * 5.0 / 9.0;