Why use finally

Question

I never properly understood the use of the finally statement. Can anyone tell me what the difference is between:

try {     a;     block;     off;     statements; } catch (Exception e) {     handle;     exception;     e; } finally {     do;     some;     cleanup; } 

on the one hand and:

try {     a;     block;     off;     statements; } catch (Exception e) {     handle;     exception;     e; } do; some; cleanup; 

On the other

Answer 1

They differ if

• the try-block completes by throwing a java.lang.Throwable that is not a java.lang.Exception, for instance because it is a java.lang.Error such as AssertionError or OutOfMemoryError.
• the try-block completes abruptly using a control flow statement such a continue, break or return
• the catch-block completes abruptly (by throwing any throwable, or using a control flow statement)

More generally, the java language guarantees that a finally block is executed before the try-statement completes. (Note that if the try-statement does not complete, there is no guarantee about the finally. A statement might not complete for a variety of reasons, including hardware shutdown, OS shutdown, VM shutdown (for instance due to System.exit), the thread waiting (Thread.suspend(), synchronized, Object.wait(), Thread.sleep()) or being otherwise busy (endless loops, ,,,).

So, a finally block is a better place for clean-up actions than the end of the method body, but in itself, still can not guarantee cleanup exeuction.