This page contains all the solutions to the different exercises in
the on-line notes pages of the PROG10082 course.
Solutions to textbook questions or programming exercises are not listed here
(ask your professor where these might be found).
public class FavouriteFoods
{
public static void main(String[] args)
{
// print my favourite foods
System.out.println("Wendi's Favourite Foods:");
System.out.println("Strawberries");
System.out.println("Chocolate");
System.out.println("Perch");
}
}
2. The minimum number of statements for Question 1 is one!
For example:
public class FavouriteFoods
{
public static void main(String[] args)
{
// print my favourite foods
System.out.println("Wendi's Favourite Foods\nStrawberries"
+ "\nChocolate\nPerch);
}
}
3.
public class Tree
{
public static void main(String[] args) {
// print a little tree
System.out.println(" *");
System.out.println(" ***");
System.out.println(" *****");
System.out.println("*******");
System.out.println(" #");
System.out.println(" #");
}
}
1. Reformat the following code segments by hand so that they follow
proper standards:
a)
public class BadCode {
public static void main(String[] args) {
// print the title of a story/book
System.out.println("Flowers for Algernon");
}
}
b)
public class BadCode {
public static void main(String[] args){
// do some calculations and print the result
System.out.print("6/4*2 is ");
System.out.println(6 / 4 * 2);
}
}
2. Add documentation to each of the corrected code segments
above.
a)
/* BadCode
*
* Version 1.0
*
* September 2012
*
* This program displays a book title on the screen.
* Programmed by Wendi Jollymore
*/
public class BadCode {
public static void main(String[] args) {
// display book title
System.out.println("Flowers for Algernon");
}
}
b)
/* BadCode
*
* Version 1.0
*
* September 2012
*
* This program displays an arithmetic
* expression on the screen with its result.
* Programmed by Wendi Jollymore
*/
public class BadCode {
public static void main(String[] args){
// display the expression
System.out.print("6/4*2 is ");
// calculate and display the result
System.out.println(6 / 4 * 2);
}
}
1. Modulus is often used to find out if a number is even or odd.
How would this work?
Answer: Any number N % 2 will be equal to 0 if the number is even, and
equal to 1 if the number is odd.
2. Rewrite each of the following expressions in proper Java syntax:
a. 3 x 4 Answer: 3 * 4
b. (x + 2)(x - 3) Answer: (x + 2) * (x - 3)
c. 10 ÷ 2 10 / 2
d. 2x - 4 2 * x - 4
1. In the table below there are 5 sets of algebraic expressions and a
corresponding incorrect Java expression. Find the errors in the Java expressions
and rewrite them correctly.
Algebraic Expression
Incorrect Java Expression
1.
(2)(3) + (4)(5)
(2)(3) + (4)(5)
2.
6 + 18 2
6 + 18 / 2
3.
4.5 12.2 - 3.1
4.5 / 12.2 - 3.1
4.
4.6(3.0 + 14.9)
4.6(3.0 + 14.9)
5.
(12.1 + 18.9)(15.3 - 3.8)
(12.1 + 18.9)(15.3 - 3.8)
2 * 3 + 4 * 5
(6 + 18) / 2
4.5 / (12.2 - 3.1)
4.6 * (3.0 + 14.9)
(12.1 + 18.9) * (15.3 - 3.8)
2. Evaluate each of the following integer expressions:
a. 20 - 5 / 2 + 3 = 20 - 2 + 3 = 21
b. 20 - 5 / (2 + 3) = 20 - 5 / 5 = 20 - 1 = 19
c. 10 * (1 + 7 * 3) = 10 * (1 + 21) = 10 * 22 = 220
d. 15 % 3 = 0
e. 10 + 5 % 2 = 10 + 1 = 11
f. 10 * 5 % 2 = 50 % 2 = 0
3. Evaluate each of the following expressions:
a. 6.0 / 4.0 = 1.5
b. 20.0 - 5.0 / 2.0 + 3.0 = 20.0 - 2.5 + 3.0 = 20.5
c. 20.0 - 5.0 / (2.0 + 3.0) = 20.0 - 5.0 / 5.0 = 20.0 - 1.0 = 19.0
d. (20.0 - 5.0) / (2.0 + 3.0) = (15.0) / (2.0 + 3.0) = 15.0 / 5.0 = 3.0
For each of the following statements below, declare a variable and
initialize it to a null value. Use the most appropriate data types and
identifier names. a. to store a customer's last name String custLastName = ""; b. to record the number of customers int numCustomers = 0; c. to record the customer's outstanding balance double custBalance = 0.0; d. to store the customer's phone number String custPhone = ""; bonus: to record a single keystroke made by the user char keystroke = '\0';
1. Find the errors in each of the following code listings:
// 1. a)
public class Qu2PartA
{
public static void main(String[] args)
{
width = 15 // missing semi-colon, data type
area = length * width; // area, length not declared
System.out.println("The area is " + area);
}
}
Corrected version:
// 1. a)
public class Qu2PartA
{
public static void main(String[] args)
{
double width = 15;
double length = 10;
double area = length * width;
System.out.println("The area is " + area);
}
}
// 1. b)
public class Qu2PartB
{
public static void main(String[] args)
{
int length, width, area;
area = length * width;
length = 20; // both of these 2 stmts should be
width = 15; // before area = length * width
System.out.println("The area is " + area);
}
}
Corrected version:
// 1. b)
public class Qu2PartB
{
public static void main(String[] args)
{
int length, width, area;
length = 20;
width = 15;
area = length * width;
System.out.println("The area is " + area);
}
}
// 1. c)
public class Qu2PartC
{
public static void main(String[] args)
{
int length = 20, width = 15, area;
length * width = area; // backwards!!
System.out.println("The area is " + area);
}
}
Corrected version:
// 1. c)
public class Qu2PartC
{
public static void main(String[] args)
{
int length = 20, width = 15, area;
area = length * width;
System.out.println("The area is " + area);
}
}
2. Do question 2.5 on page 41 and question 2.6 on page 43.
Question 2.5: Identify and fix the errors:
Line 3: the variable k is not defined anywhere. To fix: Declare the
variable k before the variable i:
int k = 3; // or whatever value you want
int i = k + 2;
Question 2.6: Identify and fix the errors:
Line 3: only i is being defined, j and k don't exist and are not being
defined in this statement. To fix:
int i = 2, int j = 2, int k = 2;
OR...
int i = 2;
int j = 2;
int k = 2;
OR...
int i = 2, int j, int k;
j = k = i;
...and there's probably a few other similar solutions, too.
3. Write a program that calculates the amount of money to tip a wait
person by coding the
following tasks:
Define a variable for the bill amount and initialize it to 35.10.
Define a variable for the tip percentage and initialize it to 15.
Define a variable for the tip amount.
Calculate the tip as the bill amount multiplied by the tip percentage
(remember that 15% = 0.15) and assign and store the result in the tip amount variable.
public class ConstTest {
// constant for the name of the college
public static final String COLLEGE_NAME = "Sheridan College";
public static void main(String[] args) {
// print out where we work/attend school
System.out.println("You attend " + COLLEGE_NAME + ".");
// change the name! o.O NOPE
COLLEGE_NAME = "Sheridan College Institute of Technology and Advanced Learning";
// print it out again!
System.out.println("You should really call it " + COLLEGE_NAME);
}
}
You should get an error when you compile
("Error: cannot assign a value to final variable COLLEGE_NAME").
The values of constant variables can never change once they're
declared and assigned!
2. Examine the code listing below. What do you think the output
should be? Write this down. Then run the program and see if you're correct.
public class Question2
{
public static void main(String[] args)
{
int factor = 2;
int sum = 10;
System.out.println("sum is " + sum);
sum *= factor;
System.out.println("sum is now " + sum);
sum *= factor;
System.out.println("sum is now " + sum);
sum *= factor;
System.out.println("sum is now " + sum);
}
}
Output should be:
sum is 10
sum is now 20
sum is now 40
sum is now 80
3. How do you think the output would change if you wrote
the program in question 2 like this:
public class Question3
{
public static void main(String[] args)
{
int factor = 2;
int sum = 10;
System.out.println("sum is " + sum);
sum *= factor;
sum *= factor;
sum *= factor;
System.out.println("sum is now " + sum);
System.out.println("sum is now " + sum);
System.out.println("sum is now " + sum);
}
}
Output will be:
sum is 10
sum is now 80
sum is now 80
sum is now 80
4.
Question 2.25:
False: not all expressions can be used as statements. For example,
the expression 5 + x is an expression, but is not a proper Java
statement. To turn it into a statement, you could assign the expression
to a variable, e.g: int y = 5 + x;
True
True (it's an assignment expression)
False (it's confusing but it is legal)
Question 2.26:
7
6
7
7
(In line 2, b receives the value of a before a is incremented)
1. What is the output from each of the following print statements?
**NOTE: using the ■ to denote a space
System.out.printf("%3d", 5);
■■5
System.out.printf("%3d", 12345);
12345
System.out.printf("%5.2f", 7.24);
■7.24
System.out.printf("%5.2f", 7.277);
■7.28
System.out.printf("%5.2f", 123.456);
123.46
System.out.printf("%5.2f", 123.4);
123.40
System.out.printf("%-5.2f", 7.277);
7.28■
System.out.printf("%-5.2f", 123.456);
123.46
2. What are the errors in each of the following print statements?
System.out.printf("%d", 23)
Missing a sem-colon!
System.out.printf("%f", 5);
%f is for floating-point numbers, but 5 is an int literal.
System.out.printf("%4d", 123.4);
%4d is an int format specifier, but 123.4 is a floating-point literal.
System.out.printf("value 1: %d value 2: d", 5, 10);
The second "d" is missing the % sign - it's treated as just the letter "d"
and the compiler will tell you that the value 10 is missing a format
specifier.
1. Write the code to declare and initialize two variables for the
numerator and denominator of a fraction (initialize each to whatever values
you wish, or use the values in the example, below). Write the code
that displays the following message dialog:
The result of numerator / denominator should be formatted to 3 decimal places.
import javax.swing.JOptionPane;
public class Exercise1 {
public static void main(String[] args) {
int numerator = 1;
int denominator = 3;
JOptionPane.showMessageDialog(null, String.format("%d/%d = %.3f",
numerator, denominator, ((double)numerator / denominator),
"Fractions", JOptionPane.INFORMATION_MESSAGE);
}
}
2. Write the code to display the values below in a single
message dialog box, one value per line. Each value should be formatted
to be right-justified, lined up at the decimal point, and showing only one
digit after the decimal point:
35
28.29
143.12
.8899
import javax.swing.JOptionPane;
public class Exercise1 {
public static void main(String[] args) {
String output = String.format("%6.2f%n%6.2f%n%6.2f%n%6.2f",
35.0, 28.29, 143.13, .8899);
JOptionPane.showMessageDialog(null, output,
"Question 2", JOptionPane.INFORMATION_MESSAGE);
}
}
1. Use Chapter 5.10 of your textbook or the Math class documentation
as a reference. What Math class methods
would you use to perform the following tasks:
find the square root of 13
Math.sqrt(13)
find the minimum value of the two numbers stored in the variables
dblNum1 and dblNum2
Math.min(dblNum1, dblNum2)
find the ceiling of -123.45
Math.ceil(-123.45)
find the floor of -123.45
Math.floor(-123.45)
find the absolute value of -123.45
Math.abs(-123.45)
2. Write a single statement to perform each of the following
calculations and store each result in a variable
of the appropriate type:
The square root of x - y
double root = Math.sqrt(x - y);
The absolute value of a2 - b2
double value = Math.abs(Math.pow(a, 2) - Math.pow(b, 2));
The area of a circle (pi multiplied by radius-squared)
double radius = Math.PI * Math.pow(radius, 2);
3. Write each of the following expressions as a single Java statement:
a.
double c = Math.sqrt(Math.pow(a, 2) + Math.pow(b, 2));
1. Define the inputs, processing, and outputs for a program that
gives the surface area and volume of a cylinder.
Inputs
cylinder radius cylinder height
Processing
surface area = 2 * PI * radius2
+ height * 2 * PI * radius volume = height * PI * radius2
Output
surface area volume
2. Define the inputs, processing, and outputs for a program that
displays the future value of an investment for a
principal P at a rate R compounded yearly for n years. The formula
for compound interest is final amount = P(1+R/100)n.
a) Develop a solution for a program that converts
a temperature from Fahrenheit to Celsius. (Celsius
temperature = 5.0/9.0 * (Fahrenheit temperature - 32.0).
Input
Fahrenheit temperature
Processing
celsius = 5.0/9.0 * (fahrenheit
- 32.0)
Output
Celsius temperature
b) Develop a solution for a program that calculates
a person's target heart rate (a target heart rate is the
heart rate you should aim to maintain while you're working
out). Use the following formula: Target Heart Rate = .7
* (220 - your age) + .3 * Resting Heart Rate (your resting
heart rate is your heart rate while you're not participating
in any physical activity).
c) Write a tip calculator that allows a restaurant or
bar customer to calculate the amount of a tip to give their
wait person. The program should allow the customer to
specify the bill amount and the percentage of tip they
would like to give.
Input
bill amount, tip percentage
Processing
tip amount = tip percentage / 100 * bill amount
Output
tip amount
d) The three ingredients required to make a bucket
of popcorn in a movie theatre are popcorn, butter, and a
bucket. Write a program that requests the cost of these
three items and the price of a serving of popcorn (assume
we have only one size). The program should then display
the profit.
Input
cost of bucket cost of butter
cost of popcorn selling price
Processing
profit = selling price - (cost of
bucket + cost of butter + cost of popcorn)
Output
profit for one bucket of popcorn
e) You would like to be able to calculate your
average grade for all the courses you've taken in first
semester. Write a program that prompts you for the grades
for the five courses you would have completed in first
term. After recording all five grades, display the
average grade on the console.
Sample output using sample data:
You entered your five grades as: 85.6 78.9 75.5 90.0 86.5
Your average grade: 83.3
1. How would you use casting to solve the problem in the
TestData example in the first section? Cast one or both of val1 and val2 into a
double value; you'll also have to declare result as a double:
double result = (double)val1 / val2
2. Using the declaration/initialization statements below,
determine the result of each of the following
explicit casts.
Scanner in = new Scanner(System.in);
System.out.print("Enter name: ");
String name = in.nextLine();
System.out.println("Do we have the same name? " +
name.equalsIgnoreCase("Freddie"));
b * d == c * c = 2 * 5 == 4 * 4 = 10 == 16 = FALSE
d % b * c > 5 || c % b * d < 7
= 5 % 2 * 4 > 5 || 4 % 2 * 5 < 7 = 1 * 4 > 5 || 0 * 5 < 7
= FALSE || TRUE = TRUE
d % b * c > 5 && c % b * d < 7
= 5 % 2 * 4 > 5 && 4 % 2 * 5 < 7
= 1 * 4 > 5 && 0 * 5 < 7 = FALSE && TRUE = FALSE
2. Given that:
a = 5
b = 2
c = 4
d = 6
e = 3
What is the result of each of the following relational expressions?
a > b = 5 > 2 = true
a != b = 5 != 2 = true
d % b == c % b = 6 % 2 == 4 % 2 = 0 == 0 = true
a * c != d * b = 5 * 4 != 6 * 2 = 20 != 12 = true
d * b == c * e = 6 * 2 == 4 * 3 = 12 == 12 = true
a * b < a % b * c = 5 * 2 < 5 % 2 * 4 = 10 < 1 * 4 = false
c % b * a == b % c * a = 4 % 2 * 5 == 2 % 4 * 5 = 0 * 5 == 2 *
5 = false
b % c * a != a * b = 2 % 4 * 5 != 5 * 2 = 2 * 5 != 10 = false
d % b * c > 5 || c % b * d < 7 = 6 % 2 * 4 > 5 || 4 % 2 * 6 < 7 = 0 * 4 > 5
|| 0 * 6 < 7 = 0 > 5 || 0 < 7 = true
d % b * c > 5 && c % b * d < 7 = 6 % 2 * 4 > 5 && 4 % 2 * 6 < 7 =
0 * 4 > 5 && 0 * 6 < 7 = 0 > 5 && 0 < 7 = false
3.
A customer's age is 65 or more: custAge >= 65
The temperature is less than 0 degrees: temperature < 0
A person's height is over 6 feet: hight > 6.0
The current month is 12 (December): month == 12
The user enters the name "Fred": userName.equals("Fred") or
userName.equalsIgnoreCase("Fred")
The user enters the name "Fred" or "Wilma"
userName.equals("Fred") || userName.equals("Wilma") OR
userName.equalsIgnoreCase("Fred") || userName.equalsIgnoreCase("Wilma")
The person's age is 65 or more and their sub total is more than $100
age >= 65 && subTotal > 100
The current day is the 7th of the 4th month
day == 7 && month == 4
A person is older than 55 or has been at the company for more than 25 years
age > 55 || numYears > 25
A width of a wall is less than 4 metres but more than 3 metres
width > 3 && width < 4
An employee's department number is less than 500 but greater than 1,
and they've been at the company more than 25 years
deptNum < 500 && deptNum > 1 && numYears > 25
4.
3.2: (try this by hand before checking your answer in your editor!)
true
false
false
true
true
true
3.3:
Neither set of statements is valid. If you go back to the lesson on
Casting and Converting, you'll notice
in the conversion chart that you can't cast a boolean into any primitive
type, and you can't cast any primitive type into a boolean.
x > y > 0: not legal - each operator requires 2 operands
x = y && y: not legal - y && y results in a boolean, which can't
be assigned to an int
x /= y: legal
x or y: not legal - or is not a valid Java operator
x and y: not legal - and is not a valid Java operator
(x != 0) || (x = 0): not legal - x = 0 is an assignment statement
3.22:
a. x % 2 == 0 && x % 3 == 0
b. x % 6 == 0
In other words, is a number that is both evenly divisible by
2 and evenly divisible by 3, also evenly divisible by 6? Yes, since
2 and 3 are both factors of 6.
3.23:
x >= 50 && x <= 100 if x is 45, 67, or 101
x is 45:
45 >= 50 && 45 <=100 = false && true = false
x is 67:
67 >= 50 && 67 <= 100 = true && true = true
x is 101:
101 >= 50 && 101 <= 100 = true && false = false
3.24:
(x < y && y < z) is true
(x < y || y < z) is true
!(x < y) is false
(x + y < z) is true
(x + y > z) is false
3.25:
age > 13 && age < 18
3.26:
weight > 50 || height > 60
3.27:
weight > 50 && height > 60
3.28:
weight > 50 ^ height > 60
6.
d
d
false
-4
7.
a)
false
2
This is probably what you would expect to get:
The entire expression evaluates to false, and x has a value of 2 after
the statement executes: (x >= 1) is true, but (x > 1) is false, so the entire
expression is false. After the evaluation of the conditions are complete, x
increments by 1 and becomes 2.
b)
false
1
This may not be the output you expected:
The expression evaluates to false, but notice that the value of x after
this expression executes is 1. This is because of the short-circuiting of the
Java && operator: Since the first condition (x > 1) is false, Java doesn't
even bother checking the second condition, so therefore the x++ is never
executed.
1. a. What would the output be if the user entered a final grade of 48?
F
1. b. What would the output be if the user entered a final grade of 55?
D
1. c. What would the output be if the user entered a final grade of 85?
D
1. d. Why doesn't this program do what it's supposed to do?
How would you rewrite it correctly?
It doesn't work because the range check
is not done properly. Since you're starting from the bottom and going up to higher
values, you should be comparing grade to the highest value in each range.
Rewrite
grades program
Question 2:
Question
2. determine interest
Question 3:
Question
3. calculate sales commission (img a, continued below...)Question
3. calculate sales commission (img b)
1. What is the output of each of the following code segments:
a)
int x = 5;
int y = 10;
int z = 2;
if (x > y) {
System.out.println("twice x is " + (x * 2));
if (x * z == y) {
System.out.println("xz equals y");
}
} else {
System.out.println(y /= z);
}
0
(the first condition x > z is false, therefore it jumps to that
if's matching else block and prints y /= z)
b)
int x = 5;
int y = 10;
int z = 2;
if (x > y) {
System.out.println("twice x is " + (x * 2));
}
if (x * z == y) {
System.out.println("xz equals y");
} else {
System.out.println(y /= z);
}
xz equals y
(the braces have moved around in this question: the if (x * z == y) is no
longer inside the if (x > y) block, so it's evaluated regardless of
the truth value of x > y)
Question 2:
Question
2. dvd rentals
Question 3:
Question
3. student residence
Question 4:
Question
4. medical fee reimbursement
Question 5:
Question
5. date validation part aQuestion
5. date validation part b
Code segment (a) is hard to read so you might want to re-write
it using proper indentation, first!
Which are equivalent? (a), (c), and (d) are equivalent to
each other.
(a) and (d) are not correctly indented (they should look
exactly like (c)); (b) and (c) are correctly
indented.
3.12
boolean newLine = count % 10 == 0;
3.13
Both (a) and (b) are correct syntactically and logically.
(b) is better because it's more efficient. With (a), the
computer will execute both if-statements and thus evaluate both
conditions, whereas in (b) it will evaluate only one condition
and only have to move to the else if the condition is false:
Therefore, (a) is more work than (b).
3.14
Segment (a):
If number is 14: 14 is even
If number is 15:
15 is is a multiple of 5 If number is 30:
30 is even 30 is a multiple of 5
Segment (b):
If number is 14: 14 is even
If number is 15: 15 is a multiple of 5
If number is 30: 30 is even
(The key here is that in (a) both if statements can be executed
if both conditions are true. In (b), the if-else block is only
executed if the if-block condition is false.)
1. For what values do each of these loops terminate?
while (recCount != 10) when recCount contains the value 10)
while (userInput.equals("")) when the userInput String object
contains characters (when it isn't empty)
while (x >= 5) when x's value becomes less
than 5
while (x < 5) when x's value becomes 5 or more
while ( (x < 5) && (y > 10) ) when x's value becomes 5 or more
OR when y's value becomes 10 or less
2. a. What do you think is the output of this loop if the user enters the value
4?
System.out.print("Enter a value to count to:");
int number = keysIn.nextInt();
int counter = 1;
while (counter <= number) {
System.out.print(counter + " ");
counter++;
}
System.out.println("\nDone!");
Solution: 1 2 3 4
Done!
2. b. How would you modify this program so that the output appears instead as:
1
2
3
4
Done!
Solution: Change the print() inside the loop to a println().
3. What is the output of the following code segment?
int counter = 1;
int sum = 0;
while (counter <= 5)
sum += counter++;
System.out.println(sum);
Solution:
15
4. What's wrong with the following program?
public class LoopProblem
{
public static void main(String[] args)
{
// print from 1 to 10 by 2's
int counter = 1;
while (counter != 10)
{
System.out.println(counter);
counter += 2;
}
}
}
Solution: You have an endless loop because counter will never be equal to 10.
5. a. Write a loop that prints the numbers from 1 to 10 with their squares, like this:
1 1
2 4
3 9
4 16
5 25
6 36
7 49
8 64
9 81
10 100
Solution:
public class Question5a {
public static void main(String[] args) {
int counter = 1;
while (counter <= 10) {
System.out.printf("%d %10d%n", counter, Math.pow(counter));
counter++;
}
}
}
5. b. How would you make the loop do the same output backwards (from 10 to 1)?
Initialize the counter to 10
Change the loop condition to counter >= 1
Change the increment to a decrement (counter--)
6. Write a while loop that counts from 1 to 20 by 2's on one line:
2 4 6 8 10 12 14 16 18 20
public class Question6 {
public static void main(String[] args) {
int counter = 2;
while (counter <= 20) {
System.out.printf("%d ", counter);
counter += 2;
}
}
}
This will work, too:
public class Question6 {
public static void main(String[] args) {
int counter = 0;
while (counter < 20) {
counter += 2;
System.out.printf("%d ", counter);
}
}
}
7. What is the output of each of the following loops?
2. If you try to pass a String into the guessAge() method,
you get an error because the method is expecting an integer, but
instead you passed it a String.
public void getPrice(int type, double yield, double maturity): an int
value, and then 2 double values
public void getInterest(char flag, double price, double time): a char
value, and then 2 double values
public void backwards(String sentence): a single string value
2.
6.12: On line 3, the 2 arguments are reversed: the method accepts
a String, then an int (see line 6) but line 3 is passing in an
int argument, then a String argument. To correct it, use:
nPrintln("Welcome to Java!", 5);
Additionally, inside the nPrintln() method, the int argument
is named "n" but there is a new local variable "n" being
declared on line 7. I will assume they don't need the local variable
at all so to fix it, remove line 7.
6.13: Pass-by-value means that a copy of an argument's value is
passed into a method parameter variable, not the original. The effect
is that you can then modify the parameter variable inside the method
and it has no effect at all on the original argument variable.
Output of a) 2
Output of b)
2
2 4
2 4 8
2 4 8 16
2 4 8 16 32
2 4 8 16 32 64
Output of c)
Before the call, variable times is 3
n = 3
Welcome to Java!
n = 2
Welcome to Java!
n = 1
Welcome to Java!
After the call, variable times is 3
1. If you change the "perim" variable's data type to an
int or to String, your program won't compile because calcPerimSquare()
returns a double, and you can't put a double into an int or a String.
2. The two statements are different in that the first one
doesn't store the return value anywhere - the perimeter returned by
the method is not stored or output. The second statement does store
the method's return value in a variable, so it can be used later.
Question 3a:
Question
3a. get alpha grade
Question 3b:
Question
3b. area and circumference of circle
4. You can find the solutions to these questions on the
textbook web site.
You get this output because when you pass the argument
"num" into the doSomething() method into parameter "n",
you are only passing a copy of the value ("pass by value").
When you modify the parameter n inside the doSomething()
method, the argument num is not affected.
This is true of all primitive variables: they are passed
by value.
2. b)
2
4
6
You get this output because when you pass an object into
a method (remember, an array is a type of object), the argument's
memory address is passed into the parameter. So for example,
if the nums array is stored at address FF88, then FF88 is passed
into the parameter "array". This means that when you access
the parameter "array" inside the doSomething() method, you are
going to the same array in memory that nums is pointing to.
In the case of objects, you "pass by reference", which means
you pass the argument's address/reference into the parameter.
The effect of this is that you can modify the object inside
the method via its parameter variable.
6.16: Ambiguous Invocation: both methods have a single int
parameter.
6.17: a) the second method is the best match because we're
passing 2 ints and the second method accepts an int and a
double. b) will also execute the second method, since it's
an exact match. c) will execute the first method, since it's
an exact match.
2.
Ambiguous Invocation for the first and third doStuff()
method: both accept a single String argument.
Question 3:
Question
3. constants I added to the programQuestion
3. the methods I added to the program
2. c) In (a), the argument values are copied into the
parameter variables, so when the parameter variables are swapped,
it has no effect on the original arguments. In (b), you're passing
the memory address of the array, not a copy of the array values.
Therefore, when you swap the 2 array elements, you're modifying the
actual array declared in the main() method.
In general, when you pass primitives, you're passing a copy of the
values into the parameter variables (pass by value). When you pass
objects, you're passing the address/reference of the argument object
into the parameter variables, which means the parameter and argument
are both referring to the same object in memory (pass by reference).
Revisit your program that calculates the difference between 2 amounts of
time.
What inputs could cause your program to crash or not function
properly?
Any value fpr hh, mm, or ss
that contains a non-digit (a symbol other than
a single decimal, a letter, etc) E.g. "ho:ho:ho" or
"1a:bc:33".
A time value with one or more missing colon symbols, E.g.
"123", "12:12", or "1.1.1".
Any value for hh, mm, or ss that is negative.
Which of those problems could be fixed with if statements or loops?
Could be fixed with ifs/loops: extract hh, mm, and ss as
String values and then manually check each character to see if
it's a non-digit.
Could be fixed with ifs/loops: get the time string and then
use String functions to check and make sure it has exactly
2 colons (this would be easy using regex).
Could be fixed with ifs/loops: extract hh, mm, and ss
and make sure each is greater than or equal to 0.
Which of those problems could not be fixed with if statements or loops?
They all could, but some of them would be a bit cumbersome.
a) What is the name of the exception that is
thrown when this code runs, and what line causes the
exception?
NumberFormatException, on the
parseInt() line.
b) What happens if you use strValue1 as the
parseInt() method's argument instead of strValue2?
Why does this happen?
You get the same exception, because
strValue1 is a floating-point number; a floating-point number can't be
parsed into an int because of the decimal point (ints can only have digits).
c) What exception is caused if you change the
last line to:
double dblValue = Double.parseDouble(strValue2);
Same exception. A double can only be digits
and one decimal point, so parseDouble() will throw a NumberFormatException
if you try to pass it anything invalid.
MP3 Player Properties:
status (on/off), current track, # of tracks,
colour, model, brand, etc. Methods:
play(), stop(), skip(), turnOn(), turnOff(), etc. Sample objects:
the old player you bought 13 years ago, your
mom's mp3 player she wears in the gym
Car Properties:
make, model, colour, number of doors,
engine type, engine status, etc. Methods:
accelerate(), decelerate(), start(),
changeGear(), etc. Sample objects:
your car, your dad's car, the car you crashed
into a snow bank
Student Properties:
student id, first name, last name, program,
gpa, address, phone number, email address,
current term, etc. Methods:
changeProgram(), register(), calculateGpa(),
dropCourse(), printTranscript(), etc. Sample objects:
you!
1. What would make 2 Room objects equal?
It can depend on context. For example, in a program that
is planning blueprints, two rooms would only be considered
equal if the length of one room equaled the length of the
second room, and the width of one room equaled the width
of the second room. For example, if room1 had a length
of 10 and a width of 20 and room2 had a length of 10 and
a width of 20, then those 2 rooms would be equal:
Note that we have to use the accessors for the room
variable because the width and length instance variables
have private access inside the room class. However, for
the current (this) room, we're inside the class itself so
it's ok to refer to length and width directly.
What if room1 had a length of 5 and a width
of 15, and room2 had a length of 15 and a width of 5?
In this case, they would not be equal because you can't take
a 5 x 15 room and replace it on a blueprint with a 15 x 5
room: they occupy the space differently. However, what if your
room class was being used in a Health & Safety application
that kept track of rooms and their occupancy? In that case
a 5 x 15 room would be the same as a 15 x 5 room because
they would both have the same occupancy, required number of
doors and emergency exits, etc. In that case, you could
simply compare the areas of the 2 rooms:
There are probably other answers, but there's the 2 most common
ones.
2. What would make 2 Time objects equal? Since this
Time class models a time on a clock, 2 times would be equal
if both of their hours were equal, both their minutes were
equal, and both their seconds were equal. Even better, you could
just compare the total seconds of each time and you'd have
a little less work to do:
public boolean equals(Object obj) {
Time time = (Time)obj;
return time.calcTotalSeconds() == this.calcTotalSeconds();
}
