Problems with compareTo method

[Amit Chohan]

Hi all
hope all is well
would someone be kind enough to help me with the following query. The following compare to method throws the following exception -

 public int compareTo(Object obj){
Appointment app = (Appointment)obj;
if (slot > app.slot)
return slot - app.slot;
else if (slot < app.slot)
return slot - app.slot;
else if (slot == app.slot)
return slot - this.slot;
} 

Error - missing return statement
public int compareTo(Object obj){
^
Thanks

[Fred Close]

I think it's because the compiler expect that there could be an other else
so this would be ok
public int compareTo(Object obj){
Appointment app = (Appointment)obj;
if (slot > app.slot)
return slot - app.slot;
else if (slot < app.slot)
return slot - app.slot;
else // i.e. (slot == app.slot)
return slot - this.slot;

}

[John Dale]

The complier doesn't consider the inter-relationsihp between the three conditions in your if statements to determine that one of the returns will always be executed. So as far as the complier is concerned, it could evalutate all three of the if conditions, not get a match, and thus fall out the bottom. You could "fix" it by adding a return 0 at the bottom.
Is there any difference between your code and

public int compareTo(Object obj) {
  Appointment app = (Appointment) obj;
  return slot - app.slot;
}

Also, don't forget that when you provide compareTo(), you usually need to override equals() and hashCode().

[Amit Chohan]

Thank you very much :roll: