1. CS Week 2
Jim Williams, PhD

2. This Week
Team Labs
Lecture: Scanner, data types, conditionals

3. Team Labs First meeting this week. 1350 cs and 1370 cs
Meet TAs & LAs, expect an Ice Breaker, be assigned a partner and do the lab together.
Pair programming

4. 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.
Import to switch roles (who has the keyboard).
Provide respectful, honest and friendly feedback

5. P1 Available P1 - Individual work Style and Commenting
Discuss concepts, don’t share assignment code
Style and Commenting

6. Piazza notes Don't post your code publicly (working or not).
You can post code from the book if you cite it.
From section 2.3.1, ...
Review the other posts (search for common terms) before posting as your question may already have been answered. Refer to these posts along with your question and say how yours is different.

7. Read In Values Recall: import java.util.Scanner;
Scanner input = new Scanner( System.in);
int age = input.nextInt();
String name = input.nextLine();

8. What are values of variables?
name: Minsub\n
age: 22\nCS
major:
name: Minsub\n22\CS
age:
name: Minsub
age: 22
String note = "Minsub\n22\nCS";
Scanner input = new Scanner( note);
String name = input.nextLine();
int age = input.nextInt();
String major = input.nextLine();

9. What are values of variables?
name: Minsub\n22\CS
age:
major:
name: Minsub
age: 22
name: Minsub
major: CS
String note = "Minsub\n22\nCS";
Scanner input = new Scanner( note);
String name = input.nextLine();
int age = input.nextInt();
String major = input.nextLine();

10. What are values of variables?
score1: 20
score2: 25
title: scores
title:
score1:
score2: scores
String note = "20 25\nscores";
Scanner input = new Scanner( note);
int score1 = input.nextInt();
int score2 = input.nextInt();
String title = input.nextLine();

11. Questions (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

12. Eclipse IDE Opening project, copying in files
Style and Commenting Guides
Strings
I/O
Calling methods
Compiler & Runtime Errors
Scanner reading a number

13. Review (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?

14. 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

15. Number Systems
Decimal
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Binary
0, 1

16. Decimal
= 302

17. Binary
= 14

18. Binary 8 4 2 1
= 5

19. Names for Numbers of Bits
bit
nibble (4 bits)
byte (8 bits)
2 bytes (16)

20. Hexadecimal (group bits by nibble)
0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = A
1011 = B
1100 = C
1101 = D
1110 = E
1111 = F

21. What character is this? 0000 0000 0100 0001 @ A Unicode:B C
Unicode:
0x003E 62 >
0x003F 63 ?
0x @
0x A
0x B
0x C

22. Color 183, 1, 1 B70101 Red, Green, Blue (RGB)
183, 1, 1
B70101
Red, Green, Blue (RGB)

23. 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, long, short, byte

24. boolean operators (comparison)
== != < <= > >=
int n = 6;
boolean result = n != 5;
result: true
result: false

25. Primitive vs Reference Data Types
Store value
Reference
Store a reference to place in memory to find value

26. java.util.Random Random randGen; //Declare reference variable
randGen = new Random(); //create instance
// randGen.setSeed( 123); //set state
int valueA = randGen.nextInt( 5); //get a value
int valueB = randGen.nextInt( 5);
int valueC = randGen.nextInt( 5);

27. Calling String methods
answer:true
answer:false
String strA = "This is a string";
char aChar = strA.charAt( 3);
boolean answer;
answer = aChar == 'i';

28. java.lang.String String strA = "This is a string"; //String literal
int lengthA = strA.length();
int lengthB = "This is a string".length();

29. Values of a1 and a2? String str1 = "Hello";
a1: true
a2: true
a1: false
a2: false
String str1 = "Hello";
String str2 = new String( "Hello");
boolean a1 = str1 == str2;
boolean a2 = str1.equals(str2);

30. Values of a1 and a2? char ch1 = 'H'; String str = "Hello";
a1: true
a2: true
a1: false
a2: false
char ch1 = 'H';
String str = "Hello";
char ch2 = str.charAt(0);
boolean a1 = ch1 == ch2;
boolean a2 = ch1.equals(ch2);

31. Calling java.lang.Math methods
double max(
double a,double b)
float max(
float a, float b)
int max(int a, int b)
double numInts = Math.pow( 2, 32);
double root = Math.sqrt( 16);
int age1 = 5;
int age2 = 25;
double big = Math.max( age1, age2);

32. Are these equivalent? boolean tired = true; if ( tired) {
Same result in all cases
Different result sometimes
Error
boolean tired = true;
if ( tired) {
//take break
tired = false; }
if ( !tired) {
//keep working
boolean tired = true;
if ( tired) {
//take break
tired = false;
} else {
//keep working }

33. Floating Down a River

34. Side Trip, maybe multiple side trips
boolean tired = true;
if ( tired) {
System.out.println(“take break”); }

35. One side of the Island or the other
boolean sunny = false;
if ( sunny) {
System.out.print(“sunny”);
} else {
System.out.print(“not sunny”); }
System.out.println( “ and back together”);

36. Equivalent? Yes No char chr = //any valid char out = 'W';
if ( chr == 'A') {
out = 'X';
} else if ( chr == 'B') {
out = 'Y';
} else {
out = 'Z'; }
char chr = //any valid
char out = 'W';
if ( chr == 'A') {
out = 'X';
} if ( chr == 'B') {
out = 'Y';
} if ( chr != 'A' || chr != 'B') {
out = 'Z'; }
Yes No

37. Dangling Else - What is out?
int value = 0;
String out = "abc";
if ( value >= 1 ) if ( value <= 10) out = "1 to 10";
else out = "else";
out: abc
out: 1 to 10
out: else
out: abcelse

38. What is the value of msg? boolean flag = true;
String msg = "before if";
if ( flag = false); {
msg = "" + flag; }
before if
true
false