AP Computer Science Exam Question

Consider the following code snippet:

public class NumberReader {
    
    public static void main(String[] args) {
        try {
            int[] numbers = {1, 2, 3, 4, 5};
            System.out.println("Enter an index to retrieve a number: ");
            int index = Integer.parseInt(args[0]);
            
            int number = numbers[index];
            
            System.out.println("Number at index " + index + " is: " + number);
        } catch (NumberFormatException e) {
            System.out.println("Invalid input format. Please enter a valid index.");
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Index out of bounds. Please enter a valid index within the range.");
        } finally {
            System.out.println("End of program.");
        }
    }
}

Explain the purpose and function of the try-catch blocks in the given code snippet. Describe the possible exceptions that can occur and how they are handled. Also, describe the behavior of the finally block.

Answer

The purpose of the try-catch blocks in the given code snippet is to handle possible exceptions that may occur during the execution of the program.

1. The first catch block, catch (NumberFormatException e), catches the exception that may occur when parsing the command-line argument (args[0]) as an integer. If the user enters a non-numeric value, such as a string, this exception will be thrown. The catch block then executes the code within it, printing the message "Invalid input format. Please enter a valid index."

2. The second catch block, catch (ArrayIndexOutOfBoundsException e), handles the exception that may occur if the user enters an index that is out of bounds of the numbers array. If the user enters an index greater than or equal to 5 (the length of the array) or a negative index, this exception will be thrown. The catch block executes the code within it, printing the message "Index out of bounds. Please enter a valid index within the range."

The purpose of the finally block is to always execute some code, regardless of whether an exception occurs or not. In this case, the finally block prints the message "End of program." This block is executed after the try block and any applicable catch blocks, providing a final piece of code that will be executed before the program terminates.

In summary, the try-catch blocks in the given code handle the exceptions related to parsing the command-line argument as an integer and accessing elements in the array by index. The finally block is used to execute code that should always be executed, regardless of exceptions.