Dan's assertion question:

[Barkat Mardhani]

Question 20
An assert statement can be used to check a control-flow invariant to verify which of the following?
a. A particular assumption is true when the flow of control enters a method.
b. The flow of control does not reach a particular point in the program.
c. The normal flow of control has reached a particular point in the program.
d. The normal flow of control has reached the end of a method.
e. The default case of a switch statement is not reached.
f. The else block of an if/else statement is not reached.

I think all of the above answer are correct. But given ansers are b,e, and f. What do you think?

[Jose Botella]

Assertions can be used for checking a conditional branch that should not be reached...

public void method() {
int a = getValue(); // returns 0, 1, or 2
if (a==0) {
// deal with 0 ...
} else if (a==1) {
// deal with 1 ...
} else {
assert a==2 : "Impossible: a is out of range";
// deal with 2 ...
}
}
////////////////////////////////////////////////////////////////////
public void method() {
int a = getValue(); // returns 0, 1, or 2
switch( a ) {
case 0:
// deal with 0 ...
break;
case 1:
// deal with 1 ...
break;
case 2:
// deal with 2 ...
break;
default:
assert false : "Impossible: a is out of range";
break;
}
}

This makes for e and f. b is a generalization of both.
Notice that with the assertion we check a conditional result not that we have reached the beginning or end of a method.
In Control flow invariants from Programming with Assertions we check a conditional, not any other point in a method.
The examples above are from The Java 1.4 Tutorial by Gregory M. Travis , which says "Do use (assertions) to check for conditional cases that should
never happen" . Not for the flow of control reaching any point in a method.
a is true as a general assertion guideline, but not for the "control flow invariant"