Control Flow as Graph

Represent execution paths through a method or function as a graph

This notional machine represents method bodies as graphs. Statements are represented as rectangles and conditions as diamonds.

This makes the possible execution paths through the different statements of a method visible and is particularly useful for explaining compound statements (loops and conditional statements), conditional expressions, and exception handling.

24 Misconceptions Expressible in this Notional Machine

A notional machine focuses on a subset of the syntax and semantics of a programming language. The following misconceptions are related to the language features expressible in this notional machine.

CatchAlwaysExecutes

Catch blocks always get executed

CatchProvidesOptions

Only the part of a catch block necessary to fix the cause of an exception is executed

ConditionalIsSequence

If-else is equivalent to sequence of two ifs

DeferredReturn

A return statement in the middle of a method doesn't return immediately

ElsIf

There is an elsif keyword for multi-way conditional statements

ElseAlwaysExecutes

The else branch of an if-else statement always executes

ForIsConditional

The body of a for statement executes at most once

IfIsLoop

The body of an if statement executes repeatedly, as long as the condition holds

IfRequiresElse

Every if statement requires an else

LoopTerminatingCondition

For and while loops end when the condition becomes true

NoShortCircuit

&& and || always evaluate both operands

PreIncrementBeforeLoop

Pre-increment in update part of for loop means increment before loop body

RecursiveCallSiteNoReturn

Tail-recursive call sites of non-void methods need no return statement

RecursiveMethodNeedsIfElse

A recursive method needs to contain an if-else statement

SuperNotFirstStatement

super() can be called anywhere in the constructor of a subclass

TryFinishes

Exceptions get thrown at the end of the try block

DeferredReturn

A return statement in the middle of a function doesn't return immediately

IfIsLoop

The body of an if-statement executes repeatedly, as long as the condition holds

NoShortCircuit

and/or always evaluate both operands

ConditionalIsSequence

If-then-else block is equivalent to sequence of two if-then blocks

ElseAlwaysExecutes

The else branch of an if-then-else block always executes

MissingElseTerminates

Blocks following an if without else will not execute if the condition is false

RepeatDistributes

Each block in a loop is repeated individually

ResetStateEachLoopIteration

The computation of all loop iterations starts from the state before the loop