101
THE COMPSCI UNIVERSITY OF AUCKLAND
SECOND SEMESTER, 2002
Campus: City and Tamaki
COMPUTER SCIENCE
Principles of Programming
(Time allowed: TWO hours)
NOTE: Attempt ALL questions.
Write your answers in the space provided.
There is space at the back for answers that overflow the allotted space
There is also a page at the back for rough working. This page will not be marked.
No Calculators are permitted
Surname
Forenames
Student ID
Login name
Question
Marks
Out of
Question 1 (Short answer)
10
Question 2 (Writing methods)
10
Question 3 (Desk-checking methods)
10
Question 4 (Classes)
15
Question 5 (ActionListener, MouseListener)
15
Question 6 (Bresenham's line algorithm)
20
Question 7 (Ethics)
20
Total
100
CONTINUED
Candidate's Name:___________________
1.
(a)
2
COMPSCI 101
What is the output shown by each of the following code fragments?
System.out.println(2+3+"^2+3^"+2+3);
(1 mark)
(b)
System.out.println(2/4*4.0+"^"+2.0/4*4);
(1 mark)
(c)
int a = 7;
int b = 3;
if( a % 3 == b % 2 )
System.out.println("Equal");
if( !(a != 3) || !(b == 3) )
System.out.println("Not");
(d)
int a = 7;
int b = 3;
if( a==7 && ( a!=4 && b+4==a) )
System.out.println("And");
if( a==3 || (a==7 && b==4) || (b!=7 || b==7) )
System.out.println("Or");
(e)
System.out.println("Before");
for(int i=0; i<0; i++)
System.out.println("Test" + i);
System.out.println("After");
(2 marks)
(2 marks)
(1 mark)
CONTINUED
Candidate's Name:___________________
(f)
3
COMPSCI 101
int a = 4;
int b = 5;
int c = 6;
int d = 7;
if( a > b && b > c )
System.out.println("a>c");
else
if( (a+d) == (b+c) ){
if( a-b < d-c)
if( a == d )
System.out.println("b > c");
else
if( a > d )
System.out.println("c > b");
else
System.out.println("unknown");
}
else
System.out.println("Confused yet?");
System.out.println("I am");
(2 marks)
(g)
int k=0;
int i=0;
for(i=0; i<3; i++);
{
System.out.println("Test" + i);
if(k == 0)
k = 2;
else
k = 0;
System.out.println(k);
}
(1 mark)
CONTINUED
Candidate's Name:___________________
4
COMPSCI 101
2. Write a method called scramble() which is used to rearrange the letters in a given
String. The letters should be rearranged into random order, based on a "key" value which is
used as the "seed" for the pseudo-random number generator used by Java.
Your method should accept a S tring and an i nt as parameters, and should return a
String which contains the same letters, but rearranged into random order. If the
scramble() method is called on two separate occasions with the same parameters, then the
characters will be arranged in the same order on both occasions. All of the letters in the
original String should be used (including all spaces and punctuation).
Example: Executing the statements:
System.out.println(
System.out.println(
System.out.println(
System.out.println(
scramble(
scramble(
scramble(
scramble(
"Hello", 100
"Hello", 200
"Have a nice
"Hello", 100
) );
) );
day", 1234 ) );
) );
would produce the output:
Hlloe
olelH
ie Hd ncyvaeaa
Hlloe
You should use the Random class in order to select the letters in the same order given the same
key value. The following extract from the Java API might prove useful here (note that you do
not have to use all the methods listed below):
java.util.Random
Constructor Summary
Random()
Creates a new random number generator.
Random(long seed)
Creates a new random number generator using a single long seed:
Method Summary
int nextInt()
Returns the next pseudorandom, uniformly distributed int value from this
random number generator's sequence.
int nextInt(int n)
Returns a pseudorandom, uniformly distributed int value between 0
(inclusive) and the specified value (exclusive), drawn from this random number
generator's sequence.
void setSeed(long seed)
Sets the seed of this random number generator using a single long seed.
CONTINUED
Candidate's Name:___________________
5
COMPSCI 101
Complete the application written here:
//import any required packages here
public class TestScramble{
//Write your method here
//Given here is some code which might be used to test your
//method
//Your method *must* produce the correct answer when different
//test cases are used
public static void main(String[] args){
System.out.println( scramble( "Hello", 100 ) );
System.out.println( scramble( "Hello", 200 ) );
System.out.println( scramble( "Have a nice day", 1234 ) );
System.out.println( scramble( "Hello", 100 ) );
}
}
(10 marks)
CONTINUED
Candidate's Name:___________________
6
COMPSCI 101
3. Desk-check the following code using the technique of diagrams shown in lectures. Show
both the diagram used to desk-check the code (on facing page) and the output produced
(below).
public class Test{
private static int method01(){
System.out.println("Method 01");
return 6;
}
private static int method02(int i){
System.out.println("Method 02");
int a = 5;
if( i % 2 == 0 )
a = method01();
return a;
}
private static int method03(int i){
System.out.println("Method 03");
int a = method02( i + 1 );
return i*a;
}
private static int method04(int a, int b){
System.out.println("Method 04");
int i = method03(a);
b = method02( method01() );
return i+b;
}
public static void main(String[] args){
System.out.println( method04(2,3) );
}
}
Show your output here:
(4 marks)
CONTINUED
Candidate's Name:___________________
7
COMPSCI 101
Show the diagram here:
(6 marks)
CONTINUED
Candidate's Name:___________________
8
COMPSCI 101
4. Below is the TestQ class definition which you need to complete. An application which
uses the TestQ class is shown on the next page. This TestQ class represents test questions.
Each new TestQ instance has a unique questionID number set from the static variable
nextID.
public class TestQ {
//static variable used to assign an id to each new Question
private static int nextID = 1;
private int questionID;
//id of question
private int marksOutOf; //number of marks question is out of
private double averageMk;
//average mark for question
private int level;
//level of difficulty of question
private String description; //description of question
public TestQ(int marksOutOf, double ave, String desc, int lev){
}
public .
getMarksOutOf(){
}
public ..
getAverageMk(){
}
public . .
toString(){
CONTINUED
Candidate's Name:___________________
9
COMPSCI 101
}
public .
hasSameLevel( .
){
}
public .
descriptionContainsWd( .
){
}
}
The Q4 application shown below uses the TestQ class. Complete the TestQ class definition
above so that the Q4 application compiles and gives the output shown on the next page.
public class Q4{
public static void main(String[] args){
TestQ q1, q2, q3;
q1 = new TestQ(10,8.5,"declaring variables",1);
q2 = new TestQ(20,14.6,"method parameter passing",3);
q3 = new TestQ(10, 6.5, "method return types",3);
System.out.println(q1.toString());
System.out.println(q2.toString());
System.out.println(q3.toString());
System.out.println();
System.out.println("Questions with better average than 70%:");
if (q1.getAverageMk()/q1.getMarksOutOf()>0.7)
System.out.println(q1.toString());
if (q2.getAverageMk()/q2.getMarksOutOf()>0.7)
System.out.println(q2.toString());
if (q3.getAverageMk()/q3.getMarksOutOf()>0.7)
System.out.println(q3.toString());
System.out.println();
System.out.println("Questions on methods");
if (q1.descriptionContainsWd("method"))
System.out.println(q1.toString());
CONTINUED
Candidate's Name:___________________
10
COMPSCI 101
if (q2.descriptionContainsWd("method"))
System.out.println(q2.toString());
if (q3.descriptionContainsWd("method"))
System.out.println(q3.toString());
System.out.println();
if (q1.hasSameLevel(q2) && q1.hasSameLevel(q3))
System.out.println("q1, q2, q3 have the same level of
difficulty");
else {
if (q1.hasSameLevel(q2))
System.out.println("q1, q2 have the same level of
difficulty");
if (q1.hasSameLevel(q3))
System.out.println("q1, q3 have the same level of
difficulty");
if (q2.hasSameLevel(q3))
System.out.println("q2, q3 have the same level of
difficulty");
}
}
}
The output obtained when the Q4 application is executed with the completed TestQ class is
shown below.
>java Q4
1: Level 1 Question:
2: Level 3 Question:
3: Level 3 Question:
declaring variables, average: 8.5/10
method parameter passing, average: 14.6/20
method return types, average: 6.5/10
Questions with better average than 70%:
1: Level 1 Question: declaring variables, average: 8.5/10
2: Level 3 Question: method parameter passing, average: 14.6/20
Questions on methods
2: Level 3 Question:
3: Level 3 Question:
method parameter passing, average: 14.6/20
method return types, average: 6.5/10
q2, q3 have the same level of difficulty
(15 marks)
CONTINUED
Candidate's Name:___________________
11
COMPSCI 101
5. The following application creates an instance of a class called Q5Frame:
public class Q5{
public static void main(String[] theFrame args){
Q5Frame = new Q5Frame("Question 5",10, 20, 250,150);
}
}
Below is the definition of the Q5Frame class which you need to complete. The behaviour of
the Q5Frame is discussed on the pages following the Q5Frame class definition shown
below.
import java.awt.*;
import java.awt.event.*;
public class Q5Frame extends Frame implements ActionListener,
MouseListener{
private final int SIZE = 20; //size of circle and square at
//each end of the line
private int x1,y1; //x,y position of the start point of the line
private int x2,y2; //x,y position of the end point of the line
private TextField x1T, y1T; //TextFields which store the x,y
//values of the start point of the line
private boolean isSelected;
//-------------------------------------------------------------//-------------- Constructor for the Frame --------------------//--------------------------------------------------------------
public Q5Frame(String title, int top, int left, int width, int
height){
setTitle(title);
setBounds(top,left, width, height);
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
dispose();
System.exit(0);
}});
setLayout(new FlowLayout());
x1T = new TextField(6);
//create the 2 TextFields
y1T = new TextField(6);
CONTINUED
Candidate's Name:___________________
reset();
show();
}
12
COMPSCI 101
//-------------------------------------------------------------//------------------------- Set the initial state -------------//--------------------------------------------------------------
public void reset(){
x1 = 150;
//set initial value for x1, y1
y1 = 100;
x2 = 200;
//set initial value for x2, y2
y2 = 60;
x1T.setText("150");//set initial values for the 2 TextFields
y1T.setText("100");
isSelected = false;
}
//-------------------------------------------------------------//------------------------- Handle ActionEvents ---------------//--------------------------------------------------------------
public void actionPerformed(ActionEvent e){
}
//-------------------------------------------------------------//------------------------- Handle MouseEvents ----------------//--------------------------------------------------------------
public void mousePressed(MouseEvent e){
}
public void mouseReleased(MouseEvent e){
CONTINUED
Candidate's Name:___________________
13
COMPSCI 101
}
public void mouseEntered(MouseEvent e){ }
public void mouseExited(MouseEvent e){ }
public void mouseClicked(MouseEvent e){ }
//-------------------------------------------------------------//----------- Display the line in the Frame -------------------//--------------------------------------------------------------
public void paint(Graphics g){
g.setColor(Color.blue);
}
}
Complete the Q5Frame class definition above so that the Q5Frame behaves as follows:
The Q5Frame first appears displaying a line from the point (x1, y1) [the start point of the line
which is surrounded by a filled circle of size 20] to the point (x2, y2) [the end point of the line
which is surrounded by a filled square of size 20]. Initially (x1, y1) which is the start point
for the line has values (150, 100) and (x2, y2) which is the end point for the line has values
(200, 60). Initially the line, the circle and the square are all displayed in the colour blue. The
Q5Frame contains two TextFields [called x1T, y1T in the Q5Frame class definition]; these
two TextFields always contain the values of the start point for the line [initially these values
are 150 for x1 and 100 for y1].
CONTINUED
Candidate's Name:___________________
14
COMPSCI 101
When the user enters new values for the start point of the line in the two TextFields and
presses ENTER in either TextField the start position of the line is set to the new values
entered by the user in the two TextFields. The left hand TextField, x1T, contains the x value
for the start point of the line.and the right hand TextField , y1T, contains the y value for the
start point of the line. Note: the end point of the line does not change when the user changes
the values for the start point of the line. The two screenshots below show the Q5Frame when
the user enters new values for the start point of the line.
Here the user has entered 50, 130 in
the two TextFields and has pressed
ENTER in one of the TextFields.
The line displayed now begins at
position (50,130).
Note: the end of the line has not
changed.
Here the user has entered 220, 120 in
the two TextFields and has pressed
ENTER in one of the TextFields.
The line displayed now begins at
position (220,120).
Note: the end of the line has not
changed.
In the Q5Frame the end point for the line is enclosed in a filled square of size 20; whenever
the user presses the mouse inside this square area the square area should be displayed in red
showing that the end point is selected. If the user has selected the end point of the line b y
pressing the mouse inside the square and then releases the mouse in a new position inside the
Q5Frame then this release point of the mouse becomes the new end point for the line; the
square area surrounding the end point is now filled with blue showing that the end point is no
longer selected. Note: the start point of the line does not change when the user changes the
position of the end point for the line. The four screenshots below show Q5Frame when the
user presses and releases the mouse to change the position of the end point of the line.
CONTINUED
Candidate's Name:___________________
15
COMPSCI 101
Here t he u ser h as p ressed the
mouse i nside t he s quare area
surrounding the end point of the
line. T he s quare area i s now
displayed in red showing that the
end point is selected.
The user has now released the
mouse in a new position inside
the Q5Frame. The end point for
the line has changed t o the
position where the user released
the mouse. The square area is
now displayed in blue showing
that the end point is no longer
selected.
Note: the start point for the line
has not changed.
Here the user has pressed the
mouse i nside t he s quare area
surrounding the end point for the
line. The square area is now
displayed in red showing that the
end point is selected.
The user has now released the mouse
in a new position inside the Q5Frame.
The end point for the line has changed
to t he p osition w here t he u ser
released the mouse. The square area
is now displayed in blue showing that
the end point is no longer selected.
Note: the start point of the line has
not changed.
(15 marks)
CONTINUED
Candidate's Name:___________________
16
COMPSCI 101
6. Consider a line that is to be drawn between the points (0,0) and (10,3).
a) Using any method you choose, identify the eleven grid points that lie closest to this
line.
(6 marks)
b) Recall Bresenham's line algorithm discussed in lectures and studied in lab 9. Java
code for this algorithm is given below.
Warning: the code actually contains a subtle error, and so the program will NOT give
the "correct" output. You must show the values this program will produce.
void line( int x1, int y1, int x2, int y2 ) {
int dx = x2 - x1;
int dy = y2 - y1;
int e = 0;
int y = y1;
for( int x = x1; x <= x2; x++ ) {
plot( x, y );
if( 2*(e + dy) > dx )
e = e + dy;
else {
y = y + 1;
e = e + dy - dx;
}
}
}
CONTINUED
Candidate's Name:___________________
17
COMPSCI 101
Perform a "desk check" using the Bresenham code above, using the same input as in
part a); i.e., the call will be to line(0,0,10,3). Show the values of the variables
x, e and y at each iteration of the loop.
(10 marks)
c) Identify and correct the error in the algorithm.
(4 marks)
CONTINUED
Candidate's Name:___________________
18
COMPSCI 101
7. Ethics
a) Name a "prima facie" principle.
(1 mark)
b) One of the reasons computers raise new and serious problems for society is the
quantity and speed by which information can be stored, retrieved and transmitted. Give
TWO additional reasons for the problems computers raise.
(4 marks)
c) Newspaper headlines reported the Therac-25 incidents as being caused by a "software
bug". Identify THREE other causal factors identified by Leveson and Turner.
CONTINUED
Candidate's Name:___________________
19
COMPSCI 101
(3 marks)
d) Recall the ethical case you were assigned in assignment five.
i) Give a concise summary of the case
(4 marks)
ii) Briefly describe the ethical principles at stake
CONTINUED
Candidate's Name:___________________
20
COMPSCI 101
(4 marks)
iii) What decision did you come to, and what justification did you use?
(4 marks)
CONTINUED
Candidate's Name:___________________
21
COMPSCI 101
Overflow Sheet
Write the question number next to your answer.
You must ALSO indicate in the allotted space that you have used the overflow sheet.
CONTINUED
Candidate's Name:___________________
22
COMPSCI 101
Overflow Sheet
Write the question number next to your answer.
You must ALSO indicate in the allotted space that you have used the overflow sheet.
CONTINUED
23
Rough Working
COMPSCI 101
You may remove this page from the exam script if you wish. This page will not be marked.
CONTINUED
24
Rough Working
COMPSCI 101
You may remove this page from the exam script if you wish. This page will not be marked.
_______________________
CONTINUED