Assignment A3: Exception Handling, Text I/O

Assignment A3 (45 marks)
Focus: Exception Handling, Text I/O
Q1. [15 marks] Write a program that creates an integer array with 50 random values, prompts
the user to enter the index of an element in the array between 0 and 49, then displays the
corresponding element value. If the specified index is out of bounds, display an error
message (e.g. “Out of Bounds”) and ask the user to enter another index. Use a while loop
that will keep prompting the user until a valid input is received. To handle invalid inputs, write
two versions of your program: one that uses exception handling, and one that uses
defensive programming. Assume a user will always enter numbers.
Sample run
Q2. [10 marks] “An InputMismatchException is thrown by a Scanner to indicate that the
token retrieved does not match the pattern for the expected type, or that the token is out of
range for the expected type”. For example, if you use the nextDouble to read a token that
is not of the type double.
Write a program that prompts the user to enter a mathematical formula (e.g., 4.3 + 5.1) and
then displays the result. Your program should prompt the user to try again if the input has an
invalid number or invalid operator (i.e., valid operators are: +, -, /, and *). Assume the user
enters spaces between the operands and the operator. Read the numbers using the
Scanner’s nextDouble method, and the operator using the next method.
Hints:
 Use a while loop that will keep prompting the user for input as long as it is invalid.
 Use a try-catch statement to check for the numbers’ validity.
 Use a selection statement (e.g., if, switch, etc.) to check for the operator’s validity.
Sample run
Q3. [10 marks] Repeat Q2 using the Scanner’s next method to read the numbers as strings and
then convert them to double using Double.parseDouble(). Run your program again and
enter an invalid number (e.g., 4.5a). What is the type of Exception that is thrown? When does
this exception happen? Modify your code to catch and handle the new exception.
Q4. [10 marks] Consider the program skeleton below:
import java.io.*;
import java.util.*;
public class CopyFileCapitalized {
 public static void main(String[] args) throws Exception {
String censoredWords[] = {"ABC", "XYZ"};
//add code (1)
 }
 private static String replaceCensoredWords(String line, String[] censoredWords){
//add code (2)
 }
}
 Write code at (2) to check line word by word and replace those which are listed in the
censoredWords array with "..." (three dots). The method should eventually return the same
line of text after replacing the censored words. One way to check the words in line is to use the
following statement and then read the words from the input stream using next().
Scanner input = new Scanner(line);
 Write code at (1) to read the contents of a text file (e.g., source.txt) line-by-line, replace censored
words using the replaceCensoredWords method, convert the text to uppercase, and write it to
a destination file (e.g., destination.txt).
Don’t worry too much about writing code to handling exceptions (just declare them in method headers).
Samples for source.txt and destination.txt can be downloaded from Canvas.
Grading:
Q1:
+7 for defensive programming,
+8 for exception handling
Q2 to Q4:
15% for logic explanation
70% for % for proper code structure and logic
15% for correct syntax and formatting

Submission Instructions
For programming questions, explain in few, simple sentences the algorithm you used to tackle the
problem. Add these sentences as a block comment at the beginning of your program. For coding
questions, make sure to use appropriate code formatting and structure (e.g., indentation, brackets, etc.).
For this assignment, you need to do the following:
1- Create a Java project of which name consists of your student number followed by the assignment
number, e.g., “1234567_A3”.
2- Create one class for each question and write your answer inside that class. Your classes should
have the same name as the question number (e.g., Q1)
3- After solving all questions, open Windows Explorer (or any other file explorer).
4- Navigate to your Java project folder (can be found inside your Eclipse workspace folder).
5- Locate the “src” folder for this project (the folder that includes the source code for all questions).
6- Zip the “src” folder and rename the zipped file to match your project name (e.g.,
1234567_A2.zip).
7- Submit the zipped file to Canvas.
Note that you can resubmit an assignment, but the new submission overwrites the old submission and
receives a new timestamp.