Worksheet
4 by Kim Ludwig
Where in a class would
the following statements normally be?
1.) import java.util.ArrayList;
(Gain access to the library)
____________________________
2.) private ArrayList notes;
(Define field notes as type ArrayList class)
____________________________
3.) notes = new ArrayList()
(Create an instance of ArrayList)
____________________________
4.) Circle
the result of the following:
int x = 0; a. X = 12
while(x
< 12) { b. X = 11
x+=3;
c. an Error
} d. x = 0
5.)
int x; a. X = 12
while(x
< 12) { b. X = 11
x+=1;
c. an Error
} d. x = 0
6.) Identify
and correct the errors in the following code. (Hint: There are 3 errors)
public void indexPrintLibrary (){
int index;
while(index > library.size()){
System.out.println("Book Number: " + (index));
((Book)library.get(Book)).printBook();
i++;
}
7.) What
will be returned by code below? ____________________
(Since you do not know the contents of myArray,
don’t be specific -- just decide what the method is doing!)
public int total (){
ArrayList myArray = new
ArrayList();
int x = 0;
Iterator iter =
myArray.iterator();
while(iter.hasNext()){
(iter.next()).print();
x++; // same as x = x + 1;
}
return x;
}
8.) Why is
it necessary to initialize a variable to a specific value before using it?
____________________________________________________________
9.) What
does an uninitialized variable contain? Do we know?
____________________________________________________________
10.) Tell the value of x after each time the following loop is executed.
int x; a. ) x =
___________
x = 3; b. ) x = ___________
y = 10; c. ) x = ___________
while ( x < y) {
d. ) x =
___________
x += y - 2; e. ) x = ___________
}
11.) Explain (specifically)
what each line of the following code is doing.
a.) String Books[ ] = new String[3]; ___________________________
b.) Books[ 0 ] = "Instant ASP
Components";_______________________
c.) Books[ 1 ]
= “Mastering XML”; ___________________________
d.) System.out.println(Books[1]); ___________________________
12.) When is
it appropriate to use a for loop?
______________________________________________________
13.) When is
it appropriate to use a while loop?
_____________________________________________________________
14.) Write a
for loop that will print all the days of the week.
String
days[ ] = new String[7];
days
[ 0 ] = "Sun"; days
[ 4 ] = “Thurs”;
days
[ 1 ] = "Mon"; days
[ 5 ] = “Fri”;
days
[ 2 ] = “Tue”; days [ 6 ] =
“Sat”;
days
[ 3 ] = “Wed”;
Answers
1. Before the class header
2. Where fields are defined or in a method
3. In a constructor or method
4. a – the loop will execute 4 times resulting
in x = 12
5. c – because x was not initialized to a
value
6.
public void
indexPrintLibrary () {
int index; int
while(index > library.size()){ index < library.size()
System.out.println("Book Number: " + (index));
((Book)library.get(Book)).printBook(); get(index)
i++;
}
7. The number of items in the array
8. Because the variable will hold some unknown
value
9. We do not know because it is not
initialized to a value.
10.
a. x = 4
b. x = 6
c. x = 10
d. x = 18
e. x = 34
11.
a. Creates an array of size 3 named Books.)
b. Adds
the String “Instant ASP Components" to the array at index
0
c.) Adds the String “Mastering XML " to
the array at index 1
d.) Prints “Mastering XML” to the terminal
window
12. When we know exactly how many times the loop
will execute
13. When we do not know exactly how many times
the loop will execute
14. for (int i = 0; i < 7; i++) {
System.out.println("Day:
" + days[i]);
}