Exception

In Java, there are two types of exceptions: checked exceptions and un-checked exceptions. A checked exception must be handled explicitly by the code, whereas, an un-checked exception does not need to be explicitly handled.

For checked exceptions, you either have to put a try/catch block around the code that could potentially throw the exception, or add a “throws” clause to the method, to indicate that the method might throw this type of exception (which must be handled in the calling class or above).

Any exception that derives from “Exception” is a checked exception, whereas a class that derives from RuntimeException is un-checked. RuntimeExceptions do not need to be explicitly handled by the calling code.

The Final Block

The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling — it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated.

Note: If the JVM exits while the try or catch code is being executed, then the finally block may not execute. Likewise, if the thread executing the try or catch code is interrupted or killed, the finally block may not execute even though the application as a whole continues.