Adapter

The adapter pattern "adapts" one class to another.

To see the value imagine that you only have access to 
binaries for DanceJudges and Person classes.



This is a class that uses the IDanceFilter interface.
-----------------------------------------------------
class DanceJudges{

    public boolean canDance(IDanceFilter iDanceFilter){
        return iDanceFilter.canDance();
    }
}
-----------------------------------------------------


This is a class that does not implemnt the IDanceFilter 
interface.
-----------------------------------------------------
class Person{

    public int graceLevel;

    public Person(int grace){
        this.graceLevel = grace;
    }
}
-----------------------------------------------------


Here is the interface.
-----------------------------------------------------
public interface IDanceFilter{
    public boolean canDance();
}
-----------------------------------------------------


This is the adapter class. This class will enable the
DanceJudges class to use the Person class as if it had
implemented the IDanceFilter interface.
-----------------------------------------------------
class PersonAdapter implements IDanceFilter{
    private Person person;    

    public PersonAdapter(Person person){
        this.person = person;
    }

    public boolean canDance(){
        if(person.graceLevel > 13)
            return true;
        else
            return false;
    }
}
-----------------------------------------------------


Test stub to show it all work.
-----------------------------------------------------
class Test{

    public static void main(String[] args){
        System.out.println("class: Test, method: main");

        Vector generalPopulace = new Vector();
        int count =0;

        DanceJudges danceJudges = new DanceJudges();

        for(int i =0; i<20; i++){
            generalPopulace.add(new Person(i));
        }
        
        for(int i=0;i<generalPopulace.size();i++){
            IDanceFilter iDanceFilter = new PersonAdapter((Person)generalPopulace.elementAt(i));
            if(danceJudges.canDance(iDanceFilter))
                count++;
        }
        System.out.println(count + " people can dance");
    }
}
-----------------------------------------------------


Here is a tar with the above java classes in it. 
adapter.tar