Use of interface, abstract

Question

Hi all
A simple question, I have been read some books or web sites about the use of interface, abstracts, but I still don't quite get it such as when should we use it, how should we apply it in terms of programming design..
Can someone teach me or show me some example....
Thanks!

Answer 1

user978043 wrote:
A simple question, I have been read some books or web sites about the use of interface, abstracts, but I still don't quite get it such as when should we use itAlmost always, especially in non-trivial cases.
how should we apply it in terms of programming design..Jverd's already given you a good example, but just to reinforce it for you: an interface describes the WHAT; a class defines the HOW.
An abstract class is somewhere between the two, and is often used for 'skeleton implementations' (you may want to Google it), which allow you to build your own concrete (non-abstract) classes very easily.
Can someone teach me or show me some example.... This one is filched from "Effective Java" and converts an array of any reference type into a fixed-length List:public static final <T> List<T> asList(final T[] array) {
   return new AbstractList<T>() {
      public T get(int index) {
         return array[index];
      public T set(int index, T value) {
         T oldValue = get(index);
         array[index] = value;
         return oldValue;
      public int size() {
         return array.length;
}In fact it's highly likely that Arrays.asList() does something very similar to the above.
Given all the neat things that a List can do, it's a pretty powerful bit of code, and only possible because of the existence of AbstractList.
HIH
Winston