Advanced Java Programming - Old Questions

2. Why do we need to handle the exception? Distinguish error and exception, Write a program to demonstrate your own exception class. [1+2+7]

An exception is an event that occurs during the execution of a program and that disrupts the normal flow of instructions. Java exceptions are specialized events that indicate something bad has happened in the application, and the application either needs to recover or exit.

Exception handling is important because it helps maintain the normal, desired flow of the program even when unexpected events occur. If Java exceptions are not handled, programs may crash or requests may fail. Suppose there are 10 statements in a program and an exception occurs at statement 5; the rest of the code will not be executed, i.e., statements 6 to 10 will not be executed. However, when we perform exception handling, the rest of the statements will be executed. That is why we use exception handling

Error vs Exception

In Java, we can create our own exceptions that are derived classes of the Exception class. Creating our own Exception is known as custom exception or user-defined exception. Using the custom exception, we can have your own exception and message. Here, we have passed a string to the constructor of superclass i.e. Exception class that can be obtained using getMessage() method on the object we have created.

Example:

class CustomException extends Exception {
   String message;
   CustomException(String str) {
      message = str;
   }
   public String toString() {
      return ("Custom Exception Occurred : " + message);
   }
}
public class MainException {
   public static void main(String args[]) {
      try {
         throw new CustomException("This is a custom message");
      } catch(CustomException e) {
         System.out.println(e);
      }
   }
}