Adapter design pattern (II)

8 March 2008

This post is in continuation to Adapter design pattern (I). Do read that before this one.

Choosing between Facade and Adapter

There is a definite difference between the Facade and Adapter. A facade is a better choice when one wants an easier or simpler interface to work with. Where as the Adapter Design Pattern is used when wrapper must support a polymorphic behavior and wrapper must respect a particular interface.

The example below demonstrates the use of Adapter Design Pattern. The adaptee class is DoubleLinkedList. The client class DoubleLinkedListPushPull instanciates adapter objects.

interface PushPull<T>
{
  void push (T o);
  T pop ();
  T top ();
}
 
//adaptee class
class DoubleLinkedList<T>
{
  public void insert (DNode pos, T o) { // code to insert}
  public void remove (DNode pos) { // code to remove}
 
  public void insertHead (T o) { // code to insert head}
  public void insertTail (T o) { // code to insert tail}
 
  public T removeHead () { // code to remove head}
  public T removeTail () { // code to remove tail}
 
  public T getHead () { // code to get head}
  public T getTail () { // code to tail}
}
 
class DoubleLinkedListPushPull<T> extends DoubleLinkedList<T> implements PushPull<T>
{
  public void push (T o) {
    insertTail (o);
  }
 
  public T pop () {
    return removeTail ();
  }
 
  public T top () {
    return getTail ();
  }
}