Programming: Exception Handling

Exception Handling Overview

Exception handling is a process in programming that responds to the occurrence of exceptions during the execution of a program.
An exception is an event or an error that occurs during the execution of a program and disrupts its normal flow.
The goal of exception handling is to provide a way to detect and report error occurrences so that appropriate action can be taken.

Exceptions are categorized as either checked or unchecked exceptions.
- Checked exceptions: These are exceptional conditions that a well-written application should anticipate and recover from.
- Unchecked exceptions: These are exceptional conditions that are external to the application, and recovery from these is usually not possible.

The try-catch-finally construct is used in exception handling.
Try block: potenially error-prone code is placed within the try block. If an exception arises, it is thrown.
Catch block: exceptions thrown from the try block are caught here. They are handled by an exception handler - a block of code that is written to manage the exception.
Finally block : comes after a try-catch block and is executed regardless of whether or not an exception is thrown. It is used to perform cleanup activities, such as closing a file or releasing a resource, ensuring that these tasks are always completed.

The throw keyword is used to explicitly throw an exception from a method or any block of code.
The throws keyword is used in method declarations where the method might throw checked exceptions, but doesn’t handle them. The calling code should handle these exceptions.

In a call stack, if a method throws an exception and it’s not caught within that method, it propagates down the call stack, and so on, until it is caught or until it reaches the bottom of the call stack. This is termed as exception propagation.

Checked exceptions are enforced at compile time, while unchecked exceptions are detected at runtime.
Checked exceptions are declared in the method’s throws clause, for example, FileNotfoundException, whereas unchecked exceptions do not need to be declared in the throws clause, for example, NullPointerException.

Exception handling is crucial to make a program robust and to prevent unexpected termination of the program.
It improves the code’s readability and flow of execution and gives an opportunity to debug issues or errors easily.