1. CS Week 4
Jim Williams, PhD

2. Lab this Week Debugging Skills Planet Explorer 1st team
work on either Terrain or Humidity map
2nd team
split up and work with others integrating your maps.

3. This and next week Challenges Conditionals, Loops, Scanner Arrays
Way of storing multiple values of same type
Single dimension, multiple dimension

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

5. What is the value of sum? 3 9 12 other int sum= 0;
boolean done = false;
for ( int i = 1; i < 4 && !done; i++) {
for ( int j = 6; j > 3; j--) {
if ( j > 4) continue;
sum += 1; }
if ( i == 3) break;
System.out.println("sum=" + sum); 3 9 12
other

6. What is the difference in the loops?
int a = 1;
while ( a < 5) {
System.out.println("hello");
a++; }
not much
not appropriate for while
for is better
for ( int a = 1; a < 5; a++) {
System.out.println("hell o"); }

7. 3 loops - Different Purposes
do { //indefinite - body executes at least once
} while ( !finished);
while ( !finished) { //indefinite - body may never execute }
for ( int i=1; i < 5; i++) { //definite

8. UML Activity Diagram (Flow Chart)

9. Arrange Code to Match Diagram
//declarations...
off = true;
System.out.println("RING, RING”);
System.out.println(“Sleeping”);
} while ( !off);
System.out.print(“Enter to snooze or ‘off’");
if ( response.equals("off")) {
off = false; }
do {
//declarations are assumed...
off = false;
do {
System.out.println(“Sleeping”);
System.out.println("RING, RING”);
System.out.print(“Enter to snooze or ‘off’");
response = input.nextLine();
off = response.equals("off");
} while ( !off);

10. Scanner num: 0 str4: 3 str4: line note. num: 3 str4:
String note = "Hmm\na \n3\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();

11. Arrays A reference type (not primitive) Hold multiple values
Access individual values with an index

12. Key Array Concepts Variable to hold array reference
Allocation of memory for the array
Initialization of the array
Accessing Array Elements

13. Which are valid ways to create arrays?
1, 2, 3, 4
1, 2, 4
3, 4 2
int [] list1; //1
int [] list2 = new int[5]; //2
int list3 = new int[]{1,2,3}; //3
int [] list4 = new int[1,2,3,4];//4

14. Which array initializations are valid?
int [] listA = new int[4]; //1
int [] listB = new int[]{8, 7, 6}; //2
Scanner input = new Scanner( System.in);
int sizeC = input.nextInt();
int [] listC = new int[ sizeC]; //3
1, 2, 3
1,3
1,2
none

15. What will this print? int [] list; list[0] = 10;
System.out.print( list[1]); 30
1020
compiler error
runtime error

16. Will these show the contents of the arrays?
both will
both won't
one but not the other
char [] chars = {'a','b','c','d','e'};
System.out.println(chars);
int [] list = {10, 2, 23, 64};
System.out.println(list);

17. What is the value of sum? int sum; int [] list = {1,3,5};9 3
compiler error
runtime error
int sum;
int [] list = {1,3,5};
sum = list[0] + list[1] + list[2];

18. What is the value of z? int [] list = new int[3]; list[1] = 6;
int z = list[3]; 3
compiler error
runtime error

19. What is the data type of listG?
String
array of String
compiler error
JVM error
String [ ] listG = {"first","middle","last"};
Try to draw a memory diagram of this.

20. Which are true? 1,2,3,4 String []arr = new String[3];
arr[0] = "hello";
arr[1] = "hello";
arr[2] = new String("hello");
System.out.println( arr[1] == "hello" ); //1
System.out.println( arr[1].equals( "hello")); //2
System.out.println( arr[2] == arr[1]); //3
System.out.println( arr[2].equals(arr[1])); //4
1,2,3,4
1,2,4
2,3,4
2,4

21. Which are true? 1,2,3,4 String []arr = new String[4];
arr[0] = "hello";
arr[1] = "hello";
arr[2] = new String("hello");
arr[3] = arr[2];
System.out.println( arr[2] == "hello" ); //1
System.out.println( arr[2].equals( "hello")); //2
System.out.println( arr[3] == arr[2]); //3
System.out.println( arr[3].equals(arr[2])); //4
1,2,3,4
1,2,4
2,3,4
2,4

22. Which are true? 1,3,4 String []arr = new String[4];
arr[0] = new String("party");
arr[1] = "party";
System.out.println( arr[0] == arr[1] ); //1
String line = scan.nextLine();
arr[2] = line;
System.out.println( arr[2] == arr[1]); //2
System.out.println( arr[2] == arr[0]); //3
System.out.println( arr[2].equals(arr[0])); //4
1,3,4
1,2,4
3,4 4

23. Which are true? 1,2 String prefix = "par"; String suffix = "ty";
String combine = prefix + suffix;
String str = "party";
System.out.println( str == combine ); //1
System.out.println( str.equals( combine)); //2
1,2 1 2
neither 1 or 2