Question

*IN JAVA*

EXCEPTION HANDLING

Concept Summary:

1. Use of try… catch in a program

2. Define an exception class and call it from the driver program.

For this lab you will complete two parts.

Part (a) of the lab implements try… catch and uses an existing exception in C# or in Java. Write a program that implements an ArrayIndexOutOfBounds error.

Part (b) writes a program that converts a time from 24-hour notation to 12-hour notation. Assume the user will enter the time as a 4-digit number with no colon.

Submission Guidelines: You will turn in 3 program files.

Part (a) has one program file

Part (b) requires two program files. (Note: C# Students can turn in one program file)

Specifications: Part (a):

Write a program in Java or C# that declares an array of 5 elements and displays the contents of the array. Your program should attempt to access the 6th element in the array (which does not exist) and using try.. catch your program should prevent the run-time error and display your error message to the user. Sample output including error message is provided below.

SAMPLE OUTPUT:

Part (a)

Printing an element out of bounds

5

7

11

3

0

You went out of limits in the array

Part (b): Define an exception class called InvalidTimeFormatException. If the user enters an invalid time like 1065 or 2515, the program should throw and handle an InvalidTimeFormatException. NOTE: Assume the user will enter the time as a 4-digit number with no colon.

SAMPLE OUTPUT:

Part (b)

Enter time in 24-hour notation:

1614

That is the same as 4:14 PM

Again? (y/n)

y

Enter time in 24-hour notation:

0245

That is the same as 2:45 AM

Again? (y/n)

y

Enter time in 24-hour notation:

1215

That is the same as 12:15 PM

Again? (y/n)

y

Enter time in 24-hour notation:

2612

Error: Hour can only be between 0 and 23

Again? (y/n)

y

Enter time in 24-hour notation:

1562

Error: Minutes can only be between 0 and 59

Again? (y/n)

n

Answer 1

a.

// IndexOutOfBoundsDemo.java : Java program to catch IndexOutOfBoundsException

public class IndexOutOfBoundsDemo {

   public static void main(String[] args)
   {

       // create an array of 5 integers
       int[] arr = {5, 7, 11, 3, 0};
       System.out.println("Printing an element out of bounds");

       // loop 6 times to try display an element at index beyond the array
       for(int i=0;i<6;i++)
       {
           try
           {
               System.out.println(arr[i]);
          
           }catch(IndexOutOfBoundsException e)
           {
               // this is executed when we try to access an element at index which is beyond the size of the array
               System.out.println("You went out of limits in the array.");
           }
       }
   }
}

//end of IndexOutOfBoundsDemo.java

Output:

b.

// InvalidTimeFormatException.java: Custom exception class which is thrown when an invalid time is encountered

public class InvalidTimeFormatException extends Exception
{
   // constructor that takes as input the exception message
   public InvalidTimeFormatException(String msg)
   {
       super(msg); // calls Exception constructor passing the message
   }
}

//end of InvalidTimeFormatException.java

// InvalidTimeExceptionDemo.java : Java program to catch InvalidTimeFormatException

import java.util.Scanner;

public class InvalidTimeExceptionDemo{

   public static void main(String[] args)
   {
       String choice;
       int time24, hour, minute;
       String tz;
       Scanner sc = new Scanner(System.in);
      
       // loop that continues till the user wants
       do
       {
           // input the time in 24 hour format as 4-digit number with no colon.
           System.out.println("Enter time in 24-hour notation: ");
           time24 = sc.nextInt();
          
           // extract the hour and minute from the input
           hour = time24/100;
           minute = time24%100;
          
           try {
               // invalid hour
               if(hour < 0 || hour > 23)
                   throw new InvalidTimeFormatException("Error: Hour can only be between 0 and 23");
               else if(minute < 0 || minute > 59) // invalid minute
                   throw new InvalidTimeFormatException("Error: Minutes can only be between 0 and 59");
               else
               {
                   // valid time, convert it to 12-hour format
                   if(hour >= 0 && hour < 12)
                   {
                       tz = "AM";
                       if(hour == 0)
                           hour = 12;
                   }else
                   {
                       tz = "PM";
                       if(hour > 12)
                           hour = hour-12;
                   }
                   // display the time in 12-hour format
                   System.out.println("That is the same as "+hour+":"+minute+" "+tz);
               }
           }catch(InvalidTimeFormatException e)
           {
               // executed when user entered time is invalid (hour/ minute)
               System.out.println(e.getMessage());
           }
          
           // ask if the user wants to input again
           System.out.println("Again? (y/n) ");
           choice = sc.next();
          
       }while(choice.equalsIgnoreCase("y"));
   }
}

//end of InvalidTimeExceptionDemo.java

Output: