1. CS Week 7
Jim Williams, PhD

2. This Week Exam 1 Results Team Lab: Loops & Eclipse Debugging
Lecture: Arrays

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

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

5. 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

6. 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

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

8. 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);

9. 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];

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

11. 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.

12. 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

13. Will this set all elements to 3?
final int START_VALUE = 3;
int [] list = new int[5];
for ( int i = 0; i < list.length -1; i++) {
list[i+1] = START_VALUE; }
Yes
Not first
Not last
Error

14. What does this code do? double value = 0.0;
find minimum value
find maximum value
compiler error
logic error
double value = 0.0;
double [] nums= {3.0,5.0,2.3,4.1};
for ( int i = nums.length; i > 0; i--) {
if ( nums[i-1] > value) {
value = nums[i-1]; }

15. Which swaps the ith and i+1th values?
temp = list[i];
list[i] = list[i+1];
list[i+1] = temp;
temp = list[i+1];
list[i] = temp;
list[i+1] = list[i];

16. What is print out? char [] list1 = new char[]{'a', 'b', 'c'};
true
false
char [] list1 = new char[]{'a', 'b', 'c'};
char [] list2 = new char[]{'b', 'b', 'c'};
System.out.println(
list1.length == list2.length);
System.out.println( list1[1] == list2[1]);

17. What is print out? System.out.println( list1 == list2);
true
false
char [] list1 = new char[]{'a', 'b', 'c'};
char [] list2 = new char[]{'a', 'b', 'c'};
System.out.println( list1 == list2);
System.out.println( list1.equals( list2));
java.util.Arrays( list1, list2);

18. Multi-Dimensional Arrays

19. Which picture of 2-D array is more accurate?
int [][] board = new int[3][2];

20. How many elements will this array hold?5 10 25
Error
int [][] board = new int[5][5];

21. What is the data type of board[3][1]?
int [][] board = new int[5][5];
int
int []
reference to int
can't access board[3][1]

22. What is the data type of board[2]?
int [][] board = new int[5][5];
int
int []
reference to int
can't access board[2]

23. What values will this array have, initially?
boolean [][] board;
board = new boolean[5][5];
false
true
none, they must be initialized first.

24. Which is correct way to set an element value?
int [][] board = new int[5][5];
board[0][0] = 5;
board[0,0] = 5;
board{0,0} = 5;
error

25. How many elements in this array?
int [][] board = {{1,2},{4,5,6}}; 5 6
ragged arrays are not valid
error

26. How would you access "Hi."? responses[1][1][1]
Error
String [ ][ ][ ] responses = {
{{"hello"},
{ "How do you do.", "Hi."}},
{{"always"},
{ "When?", "Really, always?"}} };

27. Write code to print out as a grid
4 5
int [][]grid = {{1,2,3},{4,5},{7,8,9}};
for ( int r = 0; r < grid.length; r++) {
for ( int c = 0; c < grid[r].length; c++) {
System.out.print( grid[r][c]); }
System.out.println();

28. Common Algorithms for Arrays
Searching
Sorting