Custom Exceptions

While Java provides a wide range of built-in exception classes, sometimes you need to represent an error condition that is specific to your application's domain. In such cases, you can create your own custom exception classes. This makes your code more readable and your error handling more specific. To create a custom exception, you simply define a new class that extends one of the existing exception classes in the `java.lang` package. As a general rule, if you are creating a checked exception (one that the caller should be forced to handle), your class should extend `Exception`. If you are creating an unchecked exception (representing a programming error), your class should extend `RuntimeException`. It's good practice to provide at least two constructors for your custom exception class: a default constructor with no arguments, and a constructor that accepts a `String` message. This message can then be passed up to the superclass's constructor using `super(message)`, allowing the error message to be stored and later retrieved using the `getMessage()` method. For example, in a banking application, you could create a custom `InsufficientFundsException`. When a withdrawal method detects that the balance is too low, it can `throw new InsufficientFundsException("Not enough funds to complete transaction.");`. The calling code can then have a specific `catch (InsufficientFundsException e)` block to handle this precise error scenario gracefully, perhaps by displaying a user-friendly message.