101
THE COMPSCI UNIVERSITY OF AUCKLAND
SECOND SEMESTER, 2008
Campus: City
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
No calculators are permitted
Surname:
Forenames:
Student ID number:
Login name:
Q1
Q4
(/32)
Q2
Q7
(/7)
Q5
(/11)
Q3
(/7)
Q8
(/7)
Q6
(/6)
Q10
Q11
(/7)
Q9
(/7)
(/6)
(/7)
Total
(/3)
/100
CONTINUED
-2Question/Answer Sheet
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Question 1 (32 marks)
a) What is the output produced by the following code?
System.out.println("Min is: " + Math.min(1, Math.min(0, -1)));
(2 marks)
b) What is the output produced by the following code?
int value = 13;
System.out.println( ! (6 < value) );
(2 marks)
c) What is the output produced by the following code?
int i = 5;
int[] numbers = {4, 2, -7, 5, 1, 6, 3};
System.out.println(numbers[i] + numbers[i+1]);
(2 marks)
CONTINUED
-3Question/Answer Sheet
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d) What is the output produced by the following code?
String name = "intuitive";
name = name.substring(2);
int position = name.indexOf('i');
System.out.println(name.substring(0, position + 1));
(2 marks)
e) What is the output produced by the following code?
double d = 23.7, e = 3.1;
System.out.println((int)(Math.round(d - e)));
(2 marks)
f) Complete the output which is produced by the following code.
Point p1 = new Point(4, 6);
Point p2 = new Point(3, 5);
p1.move(10, 4);
p2.translate(10, 4);
System.out.println("1: " + p1.x + ", " + p1.y);
System.out.println("2: " + p2.x + ", " + p2.y);
1:
2:
(2 marks)
CONTINUED
-4Question/Answer Sheet
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g) Complete the output which is produced by the following code.
Point p1 = new Point(4, 6);
Point p2 = new Point(4, 6);
Point p3 = p2;
p2 = new Point(p3.x, p3.y);
System.out.println("1: " + p1.equals(p2));
System.out.println("2: " + (p2 == p3));
1:
2:
(2 marks)
h) What is the output produced by the following code?
Rectangle rect = new Rectangle(20, 30, 50, 40);
Point p = new Point(rect.x + 5, rect.y + 2);
if (rect.contains(p)) {
System.out.println("Yes");
} else {
System.out.println("No");
}
(2 marks)
CONTINUED
-5Question/Answer Sheet
i)
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Complete the following code so that it produces the output:
No
Rectangle rect1 = new Rectangle(20, 30, 50, 40);
Rectangle rect2 = new Rectangle(10, 20,
,
);
if (rect1.intersects(rect2)) {
System.out.println("Yes");
} else {
System.out.println("No");
}
(2 marks)
j) What is the output when the start() method below is executed?
public void start() {
Point p1 = new Point(3, 5);
doSomething(p1);
System.out.println("1: " + p1.x + ", " + p1.y);
}
private void doSomething(Point p) {
p.x = p.x + 10;
System.out.println("2: " + p.x + ", " + p.y);
}
(2 marks)
CONTINUED
-6Question/Answer Sheet
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k) Declare a constant for the Greek letter pi and assign to it the value 3.14159.
(2 marks)
l) Write a while loop that adds together the first n positive integers, i.e.,
1 + 2 + 3 + ... + n
and stores the result in the variable, sum.
int sum = 0;
(2 marks)
m) Rewrite the following while loop into an equivalent for loop.
int i = 0;
while (i < exp) {
total = total * base;
i++;
}
(2 marks)
CONTINUED
-7Question/Answer Sheet
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n) Declare a String array variable, months.
(2 marks)
o) Construct the months array declared in n) above, so that it is large enough to hold the names
of all the months, one name per element.
months =
(2 marks)
p) Why don't you need to worry about aliasing when dealing with String objects?
(2 marks)
CONTINUED
-8Question/Answer Sheet
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Question 2 (11 marks):
Complete each of the methods below as specified in the comment preceding each method.
a)
//method to return an int twice as large as n
private int twice(int n){
}
(2 marks)
b)
//method to decide whether n1 and n2 are in ascending
//order (or of equal value)
private boolean areInOrder(int n1, int n2){
}
(2 marks)
c)
//method to tell whether one String, s1, has the same
//last character as another String, s2
private boolean sameFinish(String s1, String s2){
int lastS1 = s1.length()-1;
int lastS2 = s2.length()-1;
}
(3 marks)
CONTINUED
-9Question/Answer Sheet
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d)
//method to replicate a String, s, the number of
//times given by the int, n. For example
//reiterate("ho", 3) should return "hohoho"
private String reiterate(String s, int n){
result = "";
return result;
}
(4 marks)
CONTINUED
- 10 Question/Answer Sheet
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Question 3 (6 marks)
Complete the output produced when the following start() method is executed.
public void start() {
int n = 1;
String s = "Hello World";
String[] car = new String[3];
car[2] = "Morgan";
method1(n, s, car);
System.out.println("n: " + n);
System.out.println("s: " + s);
System.out.println("car[2]: " + car[2]);
}
private void method1(int i, String word, String[] name) {
i = 3;
word = "Goodbye";
name[2] = "Corvette";
}
n:
s:
car[2]:
(6 marks)
CONTINUED
- 11 Question/Answer Sheet
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Question 4 (7 marks)
a) Given the array definition below:
String[] monthNames =
{ "January", "February", "March",
"April", "May", "June", "July",
"August", "September","October",
"November", "December"
};
what is printed by the following statement?
System.out.println(monthNames[6]);
(2 marks)
b) Complete the printShortestMonth() method, which looks at each element in the String
array, months, and prints the element with the fewest letters in its name.
private void printShortestMonth(String[] months) {
}
(5 marks)
CONTINUED
- 12 Question/Answer Sheet
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Question 5 (7 marks):
As accurately as possible, show what would be drawn in the window by the following program. Grid
lines have been drawn on the window to help you.
The gap between adjacent gridlines is 10 pixels.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MyJPanel extends JPanel {
public void paintComponent(Graphics g){
super.paintComponent(g);
drawThing(g, 20, 40, 20);
}
public void drawThing(Graphics g, int x, int y, int size) {
g.drawOval(x, y, size * 2, size * 2);
g.drawLine(x, y + size * 3, x + size * 2, y + size * 2);
g.fillRect(x + size / 2, y + size * 3, size, size);
g.drawString("101", x + size * 3 / 2, y + size * 4);
}
}
CONTINUED
- 13 Question/Answer Sheet
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(7 marks)
CONTINUED
- 14 Question/Answer Sheet
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Question 6 (7 marks):
Complete the getAverageHeight() method which has one parameter, an array of Rectangle
objects. The method returns the average height of the Rectangles in the parameter array.
public void start() {
Rectangle[] rects = {
new Rectangle(20, 30, 50, 40),
new Rectangle(50, 60, 10, 20),
new Rectangle(10, 90, 20, 45)
};
double average = getAverageHeight(rects);
System.out.println("Average height: " + average);
}
When the above start() method is executed with the completed getAverageHeight()
method the output is:
Average height: 35.0
Notes:
The Rectangle array passed as a parameter may have any number of elements.
You may assume that there is at least one element in the parameter array and that none of
the elements are null.
CONTINUED
- 15 Question/Answer Sheet
private
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getAverageHeight (
){
}
(7 marks)
CONTINUED
- 16 Question/Answer Sheet
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Question (7 7 marks)
The following JPanel responds to MouseEvents.
Initially the JPanel displays a filled rectangle on the right hand side of the window, referred to as
the base rectangle. When the user presses the mouse, a red horizontal bar is displayed from the base
rectangle to the x position where the user pressed the mouse. If the user presses the mouse inside the
base rectangle or to the right of the base rectangle, the horizontal bar should not appear in the
JPanel.
The following screen shots show the behaviour of the completed JPanel.
The following 14 statements are part of the code. Place each number in the correct place in the
AJPanel definition on the next page so that the JPanel executes as described above.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
MouseEvent e
implements MouseListener
repaint();
private int barLeft;
addMouseListener(this);
Graphics g
public void mouseClicked(MouseEvent e) {}
barLeft = e.getX();
extends JPanel
import java.awt.event.*;
if (barLeft >= BASE_LEFT) {
barLeft = BASE_LEFT;
}
barLeft = BASE_LEFT;
g. fillRect(barLeft, BAR_Y, barWidth, BAR_HEIGHT);
int barWidth = BASE_LEFT - barLeft;
CONTINUED
- 17 Question/Answer Sheet
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import java.awt.*;
import javax.swing.*;
public class AJPanel
{
private static final int BAR_Y = 60;
private static final int BAR_HEIGHT = 20;
private
private
private
private
static
static
static
static
final
final
final
final
int
int
int
int
BASE_TOP = BAR_Y - 40;
BASE_LEFT = 350;
BASE_HEIGHT = 100;
BASE_WIDTH = 10;
public AJPanel() {
}
public void mousePressed(
){
}
public void paintComponent(
){
super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(BASE_LEFT, BASE_TOP, BASE_WIDTH, BASE_HEIGHT);
g.setColor(Color.RED);
}
public void mouseReleased(MouseEvent e){}
public void mouseEntered(MouseEvente){}
public void mouseExited(MouseEvent e){}
}
(7 marks)
CONTINUED
- 18 Question/Answer Sheet
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Question 8 (7 marks):
The JPanel defined on the next page contains one JTextField component and two JButton
components:
valueT a JTextField which contains an int value,
increaseB a JButton displaying the String, INCREASE,
decreaseB a JButton displaying the String, DECREASE.
Below is a screenshot of the JPanel when it is first displayed. The valueT JTextField
displays the number 0.
When the user presses the "INCREASE" JButton, the value in the valueT JTextField
increases by a random number between 1 and 5 (inclusive). When the user presses the
"DECREASE" JButton, the value in the valueT JTextField decreases by a random number
between 1 and 5 (inclusive).
You are required to complete the JPanel definition on the next page so that the JPanel behaves
as described above. You MUST use the variables given in the code.
The screenshots below show an example of the JPanel when the user presses the "INCREASE"
JButton twice and then presses the "DECREASE" JButton twice.
CONTINUED
- 19 Question/Answer Sheet
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import javax.swing.*;
import java.awt.*;
public class AJPanel extends JPanel
{
private JTextField valueT;
private JButton increaseB, decreaseB;
public AJPanel() {
valueT = new JTextField(5);
increaseB = new JButton("INCREASE");
decreaseB = new JButton("DECREASE");
add(increaseB);
add(valueT);
add(decreaseB);
}
public void
(
e) {
CONTINUED
- 20 Question/Answer Sheet
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}
}
(7 marks)
Question 9 (3 marks):
The Time24Hour class has two int instance variables, hour and minutes. Complete the
equals() method for the Time24Hour class. This method returns true if both objects
represent the same time, false otherwise.
public boolean equals(Time24Hour other) {
}
(3 marks)
CONTINUED
- 21 Question/Answer Sheet
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Question 10 (6 marks):
In the following Bank class:
public class Bank {
//put instance variables here
public Bank(Person manager, Time24Hour openTime, int
tellers) {
//put the constructor code here
}
... other code omitted ...
}
(6 marks)
a) declare three instance variables:
an instance variable, manager, of type Person,
an instance variable, openingTime, of type Time24Hour, specifying the
bank opening time,
and
an instance variable, maxTellers, of type int, specifying the maximum
number of teller positions.
b) complete the constructor which has the following 3 parameters:
a Person parameter which specifies the person who is the manager,
a Time24Hour object which specifies when the bank opens,
and
an int which specifies the maximum number of tellers.
CONTINUED
- 22 Question/Answer Sheet
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Question 11 (7 marks)
You are required to complete the following JPanel which uses a Timer object. The Timer object is
created with a delay of 100 milliseconds. Initially nothing is displayed inside the JPanel except a
thin rectangle down the right hand side of the window. The Timer starts when the user first presses
the UP arrow key.
When the Timer starts, a black line, which increases in length, appears from the left hand side of the
JPanel. The length of the line increases by ten pixels with each tick of the Timer, i.e. the end of the
line increases by ten pixels each time as the line grows to the right. When the end of the line
reaches 200, the line starts shrinking, i.e. the end of the line decreases by ten pixels. When the
length of the line is zero, the line starts growing again.
By pressing the UP and DOWN arrow keys, the user controls when the line starts and stops
growing/shrinking. When the user presses the UP arrow key, the Timer should start and the line
continues growing/shrinking. When the user presses the DOWN arrow key, the Timer should stop.
When the user presses the UP arrow key again, the Timer starts again and the line continues
growing/shrinking, etc.
Below are some screenshots of the JPanel in action.
The first screenshot shows the JPanel when it is first displayed.
The next five screenshots show the JPanel after the user has pressed the UP arrow key and the line
has started growing.
The next three screenshots show the line shrinking after the end of the line has reached 200 pixels.
The last two screenshots show the line growing again after the end of the line has shrunk to 0 pixels.
Notes:
The start of the line is ALWAYS given by the constants:
public static final int LINE_LEFT = 0;
public static final int LINE_DOWN = 50;
You MUST use the variables and constants given in the code.
When the user first presses the UP arrow key the line starts increasing its length.
CONTINUED
- 23 Question/Answer Sheet
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import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class AJPanel extends JPanel
{
//The start of the line
public static final int LINE_LEFT = 0;
public static final int LINE_DOWN = 50;
private int lineEnd;
private boolean isIncreasing;
private Timer t;
public AJPanel() {
isIncreasing = true;
lineEnd = LINE_LEFT;
}
public void actionPerformed(ActionEvent e) {
}
CONTINUED
- 24 Question/Answer Sheet
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public void keyPressed(KeyEvent e) {
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
//the thin rectangle displayed on the right
//hand side of the window
g.fillRect(200, 0, 4, 150);
}
public void keyReleased(KeyEvent e) {}
public void keyTyped(KeyEvent e) {}
}
(7 marks)
CONTINUED
- 25 Question/Answer Sheet
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OVERFLOW PAGE
(If you have used this page, please indicate clearly under the
relevant question that you have overflowed to this page)
CONTINUED
- 26 Question/Answer Sheet
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OVERFLOW PAGE
(If you have used this page, please indicate clearly under the
relevant question that you have overflowed to this page)
CONTINUED
- 27 Question/Answer Sheet
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ROUGH WORKING (WILL NOT BE MARKED)
(You may use this page for rough working)
CONTINUED
- 28 Question/Answer Sheet
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ROUGH WORKING (WILL NOT BE MARKED)
(You may use this page for rough working)