Java Practices->Exceptions and control flow

Exceptions and control flow

When an exception occurs within a method, the control flow defined by Java can take several forms.

If an exception occurs outside a try..catch block, the exception simply propagates "up" to the caller.

If an exception occurs inside a try..catch block, then the control flow can take different forms. Here are the cases, along with indicators for which code blocks are included in the control flow:

Case	try	catch	finally	bottom
`try` throws no exception	y	-	y	y
`try` throws a handled exception	y	y	y	y
`try` throws an unhandled exception	y	-	y	-

Here, "bottom" refers simply to any code which follows the finally block, as shown here :

final class Bottom {

  void doStuff() {
    try {
      //..elided
    }
    catch( Exception ex ) {
      //..elided
    }
    finally {
      //..elided
    }
    //any code appearing here, after the finally
    //block, is "bottom" code
  }
}

There is a misconception - especially common among C programmers migrating to Java - that exceptions can be used to define ordinary control flow. This is a misuse of the idea of exceptions, which are meant only for defects or for items outside the direct control of the program.