1. CS Week 8
Jim Williams, PhD

2. This Week Team Lab: Arrays and Hangman Lecture:
drawing diagrams (bring paper and pencil)
Lecture:
More Arrays and Methods
Unit Testing

3. How To Study?

4. Question 37 / Lab 2, Exercise B, L.
String exprStr1 = " = 4 + 1";
String exprStr2 = "4 + 1 = " ;
String exprStr3 = "4 + 1 = " + (4 + 1);

5. Question 6 / Lab 3, Exercise B, K:
Random numGenerator = new Random();
int num1 = numGenerator.nextInt(10);
int num2 = numGenerator.nextInt(10);
int num3 = numGenerator.nextInt(10);
//Does the value returned from nextInt method call change each time?
//What are the possible values returned?

6. Question 9 / Lab 4, Exercise B, G:
boolean flag = false;
if ( flag = true) {
System.out.println("flag is true");
} else {
System.out.println("flag is false"); }

7. Question 11 / Lab 5, Exercise B, N:
String str2 = null;
if ( str2.length() >= 1 && str2 != null) {
System.out.println( str2);
} else {
System.out.println("null or zero length string"); }

8. Draw a picture
int [] items = new int []{5,6,7};

9. What does this do? int [] list = new int[4];
set each element to i * 2
0, 2, 4, 6
compiler error
runtime error
int [] list = new int[4];
for ( int i = 0; i <= list.length; i++) {
list[i] = i * 2; }
try it.

10. Is it possible for methodC to change the contents of the array?
public static void main(String []args) {
char [] items = new char[]{'c','b','a'};
methodC( items); }

11. Where in memory is variable z?
stack
heap
it is local
Error
public static void main(String []args) {
int r = 3;
int c = 4;
int [][] z = new int[r][c]; }
A and C are both correct. Local variables are those declared within methods and are stored in the stack.

12. Can you call this method to get the new array?
yes no
reference lost
Error
public static int [] createList(int size) {
return new int[size]; }
public static void main(String[]args) {
int [] list = createList( 10);
list[3] = 10;
try it.

13. Can main see the changed value within list?
yes no
reference lost
Error
public static void changeList(int [] list) {
if ( list.length > 0) {
list[0] = 10; }
public static void main(String []args) {
int [] z = new int[5];
changeList( z);
System.out.println( z[0]);
try it.

14. Can you call this method to get the new array?
yes no
reference lost
Error
public static void createList(int [] list) {
list = new int[10]; }
try it.

15. What prints out? num:10 list:[1, 2, 11] num:11 list:[1, 2, 3]
static void change( int num, int [] list) {
num = 11;
list[2] = num; }
public static void main( String [] args) {
int [] list = {1,2,3};
int num = 10;
change( num, list);
System.out.println("num:" + num
+ "\nlist:" + Arrays.toString( list));
num:10
list:[1, 2, 11]
num:11
list:[1, 2, 3]
list:[1, 2, 10]
try it.

16. What prints out? num:10 list:[1, 2, 11] list:[4,5,10] list:[1, 2, 3]
static void change( int num, int [] list) {
list = new int[]{4,5,6};
list[2] = num; }
public static void main( String [] args) {
int [] list = new int[] {1,2,3};
int num = 10;
change( num, list);
System.out.println("num:" + num
+ "\nlist:" + Arrays.toString( list));
try it.

17. Can you call this method to get the new array outside the method?
yes no
sometimes
Error
static void createBoard(int [][] board) {
board = new int[3][3]; }
try it.

18. Can you call this method to get the new array?
yes no
reference lost
Error
static int [][] createBoard(int r, int c) {
return new int[r][c]; }
try it.

19. Can main see the changed value within list?
yes no
reference lost
Error
public static void changeList(int [][] list) {
list[0] = new int[3];
list[0][1] = 9; }
public static void main(String []args) {
int [][] z = new int[5][5];
changeList( z);
System.out.println( z[0][1]);
try it.

20. Will this initialize the array to all 1's?
yes no
don't know
Error
public static void main(String []args) {
int [][] board = {{2,3},{4,3,2}};
initBoard( board); }
static void initBoard(int[][] board) {
for ( int i = 0; i < 2; i++)
for ( int j = 0; j < 3; j++)
board[ i ][ j ] = 1;
try it.

21. Will this initialize the array to all 1's?
yes no
don't know
Error
public static void main(String []args) {
int [][] board = {{2,3},{4,3,2}};
initBoard( board); }
static void initBoard(int[][] b) {
for ( int i = 0; i < b[i].length; i++)
for ( int j = 0; j < b[j].length; j++)
b[ i ][ j ] = 1;
try it.

22. Will this initialize the array to all 1's?
yes no
don't know
Error
public static void main(String []args) {
int [][] board = {{2,3},{4,3,2}};
initBoard( board); }
static void initBoard(int[][] b) {
for ( int i = 0; i < b.length; i++)
for ( int j = 0; j < b[ i ].length; j++)
b[ i ][ j ] = 1;
try it.

23. Unit Testing (method) Developer Writes method to meet specification
Tester
Verifies that method meets specification

24. Specification /** * This method returns the number of 9s in the table.
table a 2 dimensional array of int
the number of 9s in table */
public static int num9s(int [][]table) {
return -1; }