Question

I’m not getting inner classes. What’s the reason for using inner classes in Java? Can you give me a good example of static and non static nested classes? What are the advantages / disadvantages of it?
Cheers

Answer 1

Anonymous inner classes are useful for defining one-shot classes with very few methods, for instance when implementing an event listener or a comparator. In these cases, a full-blown class would be overkill, given that it’s not going to be used anywhere else.

Here’s a simple example of a comparator for a string list implemented as an anonymous inner class:

Collections.sort(myArrayList, new Comparator() {
    public int compare(Object a, Object b) {
        return ((String) a).compareToIgnoreCase((String) b);
    }
});

Or if myArrayList happens to be a generic list, this is how it would look like:

Collections.sort(myArrayList, new Comparator<String>() {
    @Override
    public int compare(String a, String b) {
        return a.compareToIgnoreCase(b);
    }
});