Newbie: Method should or should not have side effects

Question

Hi experts,
What does it really mean when I read for the InputVerifier class that the method 'shouldYieldFocus' can have side effects but the method 'verify' should not have side effects.
Thanks for you comments.
tuckie

Answer 1

I am but a newbie only asked to learn and maintain. The reason I ask about side effects is that the shouldYieldFocus() method is invoked twice for the same tab key event. When the tab key (or mouse click) wants to move focus to another input the current input's shouldYieldFocus() is invoked, it in turn invokes verify() which validates data returning true or false and checks to see if a warning should be issued that the data is legal but high. If the data is not high it also returns true and the focus is yielded. Also shouldYieldFocus() is only invoked once. It is when the data is high and the showConfirmDialog() is put up that I get the second shouldYieldFocus() invocation. The previous coder put in a de-bouncing mechanism and I think this is where/how the problems with the next field are created. Sometimes the next field's focusLost() is invoked without the operator making any input. The focusLost() does some fill in the blank things that are reasonable only if the operator really wanted not to fill in any data in the field.
Back to my original point, I was wondering if the fact that the verify() method may have a dialog box put up before it returns to shouldYieldFocus() is the kind of thing that shouldn't be done - no side effects. If so then it could be the likely cause of the problem with the next field sometimes being automatically filled in as if it had received a focusLost() event.
tuckie