Control Flow

Why do we have control flow in programs at all? There are languages like Prolog that don’t have an explicit notion of a flow of control. Bits of logic float around in a soup, waiting for the right conditions before becoming active.

Java is a member of the family of languages in which the sequence of control is a fundamental organizing principle. Adjacent statements execute one after the other. Conditionals cause code to execute only in certain circumstances. Loops execute code repeatedly. Messages are sent to activate one of several subroutines. Exceptions cause control to jump up the stack.

All of these mechanisms add up to a rich medium for expressing computations. As an author/programmer, you decide whether to express the flow you have in mind as one main flow with exceptions, multiple alternative flows each of which is equally important, or some combination. You group bits of the control flow so they can be understood abstractly at first, for the casual reader, with greater detail available for those who need to understand them. Some groupings are routines in a class, some are by delegating control to another object.