Adapters

class MyClass implements Interface2
{
 private Interface1 object;
 MyClass(Interface1 object)
 {
  this.object = object;
 }
// This is where we put the Interface2 methods 
// that call Interface1 methods
}

The basic idea is that the MyClass class converts (adapts) one interface to the other.

interface AlphaList
{
 void add(int value);
 void insert(int index, int value);
 int get(int index);
 void set(int index, int value);
 int count();
 void remove(int index);
}

AlphaList is one of the interfaces that allows the framework code to interact with the code that uses the framework.

class AlphaListManager
{
 public static AlphaList createList()
 {
  //some code to create an object
 }
}

interface BetaList
{
 int getValue(int index);
 void setValue(int index, int value);
 int getSize();
 void setSize(int newSize);
}
class BetaSaveManager
{
 public static void saveList(BetaList list)
 {
  //some code to save a BetaList object
  //to a file on disk
 }
}

BetaList is one of the interfaces that allows the framework code to interact with the code that uses the framework.

BetaSaveManager is a class in the framework. Its saveList method saves a BetaList object

class ListAdapter implements BetaList
{
 private AlphaList list;
 ListAdapter(AlphaList list)
 {
  this.list = list;
 }

 int getValue(int index)
 {
  return this.list.get(index);
 }

 void setValue(int index, int value)
 {
  this.list.set(index, value);
 }

 int getSize()
 {
  return this.list.count();
 }

 void setSize(int newSize)
 {
  if (newSize > this.list.count()
  {
   while (this.list.count() < newSize)
  {
   this.list.add(null);
  }
 }
 else if (newSize < this.list.count() {
   while (this.list.count() > newSize)
   {
    list.remove(list.count() - 1);
   }
  }
 }
}

The ListAdapter class implements the BetaList interface from the second framework.

When someone calls these methods, the class code «forwards» the calls to the list variable, which is an AlphaList from the first framework.

An AlphaList object is passed to the ListAdapter constructor

The setSize method operates according to the following rules: if the size of the list must be increased, add empty (null) items. If the size of the list needs to be reduced, delete items at the end.

public static void main(String[] args)
{
 AlphaList listAlpha = AlphaListManager.createList();
 BetaList listBeta = new ListAdapter(listAlpha);
 BetaSaveManager.saveList(listBeta);
}