Exceptions and Error Handling

Exception

An event occurring during program execution that disrupts the normal flow of instructions.

Checked exception

A category of exceptions that the compiler mandates must either be caught or declared with the throws keyword.

Unchecked exception

A runtime exception that the compiler does not require you to explicitly catch or declare.

Handling difference between checked and unchecked exceptions

Checked exceptions require mandatory handling or declaration at compile time, whereas unchecked exceptions do not.

Common examples of unchecked exceptions

NullPointerException, ClassCastException, and ArithmeticException.

Defining a custom exception

Create a new class that extends Exception or one of its relevant subclasses.

throw keyword

Explicitly triggers and raises an exception from within a method or block of code.

throws keyword

Specifies in a method signature which exceptions the method can propagate to its caller.

Purpose of a try block

Encloses a segment of code that has the potential to raise an exception.

Purpose of a catch block

Catches and handles a matching exception thrown by an associated try block.

Choosing try/catch over throws

Use try/catch to resolve the problem locally; use throws to pass handling responsibility back to the caller.

Testing whether a method throws an exception

Execute assertThrows() by supplying the expected exception class alongside the executable code.