1. CS 200
Branches
Jim Williams, PhD

2. This Week Team Lab: Using Objects, take paper Thursday:
P3 due
Pre-Exam 1: bring WISC ID, #2 Pencils
6 questions, 15 minutes
Consulting hours: Request Help Queue
Lecture: Branches

3. Best statement? x = rand.nextInt(10)-2;
What is the best statement to get a value between 2 and 10, inclusive of both 2 and 10?
Assume:
Random rand = new Random();
int x;
//x = ???
x = rand.nextInt(10)-2;
x = rand.nextInt(9)+1;
x = rand.nextInt(8)+2;
x = rand.nextInt(9)+2;
Other
try it.

4. What are values of variables?
String note = " C S\n2 \n33\n end\n";
Scanner input = new Scanner( note);
String str1 = input.nextLine();
int num1 = input.nextInt();
String str2 = input.next();
String str3 = input.nextLine();
num1: 2
str2: "33"
str3: ""
str2: " \n33"
str3: "\n end"
str3: " end"

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

6. Relational and Equality Operators
< <= > >= == !=
int n = 6;
boolean result = n != 5;
result: true
result: false

7. Logical Operators && (AND) both sides true to be true, else false
|| (OR) either side true then true, else false
! (NOT) if true then false, and vice-versa
!(a && b) == !a || !b //is this true or false?

8. What is result? boolean result = flag = false || flag; Truth Table:
try it.

9. Does !(a && b) == !a || !b Truth Table: a b a && b !(a && b) !a !b

10. Are these equivalent? boolean tired = true; boolean tired = true;
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 }

11. Floating Down a River

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

13. 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”);

14. Today pre-midterm 1 Lecture: continue with Branches
6 questions, 15 minutes
Lecture: continue with Branches

15. 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

16. Switch: What is printed out?
char choice = 'a';
switch (choice) {
case 'a': System.out.print("a");
case 'b': System.out.print("b");
break;
default: System.out.print("other"); } a b ab
other

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

18. Comparing: == vs equals()
Primitive data types
use == for comparing primitive values
No equals() method for primitive data types
(but there is equals() method in wrapper classes)
Reference data types
use == for comparing references
use equals() for comparing instance/object contents
The meaning of equals() depends on the class it is defined in.

19. What is printed out? true *compiler error false int i = 6; int j = 6;
System.out.println( i == j);
System.out.println( i.equals( j));
Integer k = new Integer( 7);
Integer m = new Integer( 7);
System.out.println( k == m);
System.out.println( k.equals( m));
true
*compiler error
false

20. 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);

21. String: == vs equals() String str1 = "hello"; String str2 = "hello";
String str3 = new String("hello");
String str4 = "hello";
System.out.println( str1 == "hello" );
System.out.println( str1 == str2);
System.out.println( str1.equals("hello"));
System.out.println( str3 == str1);
System.out.println( str3.equals( str2));

22. Scanner Scanner input = new Scanner("1 \ntwo \n 2\n\n");
int a = input.nextInt();
if ( input.hasNextInt()) {
int b = input.nextInt();
} else {
input.nextLine(); }
String line = input.nextLine();
System.out.println("#" + line + "#");

23. Scanner num: 0 str4: 3 str4: line note. num: 3 str4:
String note = "Hmm\na \na\n3\n\nline note.";
Scanner input = new Scanner( note);
int num = 0;
String str1 = input.nextLine();
String str2 = input.next();
if ( input.hasNextInt()) {
num = input.nextInt(); }
String str4 = input.nextLine();

24. Debugging with Print statements
See what is going on.
Divide and conquer.