AP Computer Science Exam Question

You are given the following Java code:

public class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public class ExceptionTester {
    public void testMethod(int num) throws CustomException {
        if (num < 0) {
            throw new CustomException("Number must be positive");
        } else if (num > 100) {
            throw new CustomException("Number must be less than or equal to 100");
        }
    }

    public static void main(String[] args) throws CustomException {
        ExceptionTester tester = new ExceptionTester();
        try {
            tester.testMethod(-5);
            tester.testMethod(500);
            tester.testMethod(50);
        } catch (CustomException e) {
            System.out.println(e.getMessage());
        }
    }
}

Explain the output of the above code when executed.

Answer

The output of the above code when executed will be:

Number must be positive
Number must be less than or equal to 100

Explanation:

The ExceptionTester class defines a method testMethod that takes an integer num as a parameter and throws a CustomException depending on the value of num. If num is less than 0, the method throws a CustomException with the message "Number must be positive". If num is greater than 100, the method throws a CustomException with the message "Number must be less than or equal to 100".

In the main method, an instance of ExceptionTester is created. Then, the testMethod is called three times with different values: -5, 500, and 50. Each of these calls is wrapped inside a try-catch block where the catch block catches the CustomException and prints its message using e.getMessage().

When the testMethod is called with -5 as the argument, it throws a CustomException with the message "Number must be positive". This exception is caught by the first catch block, and the message "Number must be positive" is printed.

Next, when the testMethod is called with 500 as the argument, it throws a CustomException with the message "Number must be less than or equal to 100". This exception is caught by the second catch block, and the message "Number must be less than or equal to 100" is printed.

Finally, when the testMethod is called with 50 as the argument, no exception is thrown. Hence, nothing is printed for this call.

Therefore, the output of the code is:

Number must be positive
Number must be less than or equal to 100