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Invariants: Postconditions
Point Move Postcondition
Task: Pass tests.PointMovePostcondition
.
A postcondition of the move
operation of a Point
is that the coordinates should change accordingly. If a call to move
didn't actually move a point by the desired offset, then the point is in an illegal state and so an IllegalStateException
should be thrown.
around
advice. Note that because we're dealing with how the coordinates change during move, we need access to the coordinates both before and after the move, in one piece of advice.
When the access to the old coordinates and move arguments has been established, the check comes down to essentially the following code: (where dx
and 'dy are the arguments given to the
move operation)
<code aspectj>
if(p.getX() - oldx != dx || p.getY() - oldy != dy)
throw new IllegalStateException();
</code>
With a correct implementation, you should pass the tests of suite
tests.PointMovePostcondition.
===== Bounds Move Postcondition =====
Task: Pass
tests.BoundsMovePostcondition.
FigureElement objects have a
getBounds() method that returns a
java.awt.Rectangle representing the bounds of the object. An important postcondition of the general
move operation on a figure element is that the figure element's bounds rectangle should move by the same amount as the figure itself. Write an aspect to check for this postcondition – throw an
IllegalStateException if it is violated.
<note tip>
The check can be less technical than in the previous case if you employ the
Rectangle API:
- Employ the copy constructor to create a clone of the original bounds.
- Replay the move on the clone with the
translate method.
- Compare the result to the actual new bounds using the
equals method.
</note>
A correct implementation should pass the tests of suite
tests.BoundsMovePostcondition''.
When done, remove the aspect from the build path and continue with the Authentication track.