Instanceof in combination with switch

Question

Hi,
I have a vector that can contain Objects from
different classes. When the vector arrives in the
EJB I want to perform different actions dependend
of the Class of the object.
I want to do this in a switch statement using instanceof,
but I can't make it work.
Object aRecord = difRecords.elementAt(0)
switch(??)
case ??:
case ??:
Can anybody help me with this?
Regards,
Sven

Answer 1

You can't use switch in this way, only with primitives like int.
You'll have to take the wordy longsmith approach and use if... else..., unless you have an array of type Class whose ordinals are then used in the switch, e.g.:final Class[] CLASSES = {
  Class.forName("java.lang.String"),
  Class.forName("java.lang.Integer"),
  /*etc.*/,
  Class.forName("java.lang.String")
final int CLASS_STRING = 0;
final int CLASS_INTEGER = 1;
/*etc*/
final int CLASS_UNKNOWN = 9;  // or however big the array of class names
Object aRecord = difRecords.elementAt(0);
//Get the int value representing the class of this element...
//(Will be 9=UNKNOWN if not any of the other classes in CLASSES array)
for(int classOrd = 0; classOrd < CLASS_NAMES.length && aRecord.getClass() != CLASSES[classOrd]; classOrd++);
switch(classOrd){
  case CLASS_STRING:
    //Do stuff for String...
    break;
  case CLASS_INTEGER:
    //Do stuff for Integer...
    break;
  /*etc.*/
  case CLASS_UNKNOWN:
    //Handle unknown class
}The reason for having java.lang.String appear at the beginning and end of the array is that, if the object is a String, it will be recognised as CLASS_STRING (classOrd for the switch block); if it's any of the other classes in CLASSES array, it will be recognised as CLASS_XXX.
If it's not recognised, it will get to java.lang.String the second time; you now know it's not a recognised class so assign CLASS_UNKNOWN to classOrd.
Might be a bit over the top but I'm sat here pondering a pain-in-the neck Windows problem and took this as a welcome excuse for distraction!
Hope it helps, or maybe convinces you to stick with if... else... ;-)
Chris.