Question

Hey guys im stuck on a problem.
Say I have an interface Animal. I then have classes that implement it such as Dog, Cat, Goat. say each of these classes has an update() function that they get from the interface.

I have an arraylist of Animal,that includes all different kinds of the animal classes (dog, cat, goat). If i was given a string that says “Goat” how would i search that arraylist and choose only the Goat update() function, ignoring Dog and Cat…

Answer 1

for ( Animal a : animals ) {
    if ( a instanceof Goat ) {
       a.update();
    }
}

If you really only have the String “Goat” to go on you could do something like this:

if ( a.getClass().getName().endsWith("Goat") ) {
    //...

Or if the String has nothing to do with the name of the class, you could map a String to an instance of Class:

Map<String, Class<? extends Animal>> map = new HashMap...
map.put("Goat", Goat.class);

//...
if ( map.get("Goat").isInstance(a) ) {
   a.update();
}

In my opinion Google’s Guava is the best choice:

 for ( Goat g : Iterables.filter(animals, Goat.class) ) {
    g.update();
 }