problem of "[super dealloc]"

- (void)dealloc {
   [super dealloc];  
   [a release];
   [b release];
}


- (void)dealloc {
    [a release];
    [b release];
    [super dealloc];
}

What's the difference between them?

If a or b extends super!!!!! [super dealloc] at front will lead problems