Perspective for Java technologies : implementing interface on late.

Question

In Java, to implements the adapter pattern's; we have to create a new class that have a link with the adaptee class and implements the adapter interface.
class MyAdapter implements IAdapter
      public MyAdapter( Adaptee a );
}or, if we need protected methods :
class MyAdapter extends implements IAdapter
     public MyAdapter( Adaptee a );
}then, to call the method void foo( IAdapter i ); ;
we have to do xxx.foo( new MyAdapter( adaptee ) );it could be simpler if java allowed to implement interfaces after defining the java class.
public class Adaptee
}and then, in another file, something like,
implementation of  IAdapter for class Adaptee
}would be equivalent to
public class Adaptee implements IAdapter
}The advantage of the first method is that you can adapt very easy external classes from external jar file.
thank's for coments.

Answer 1

An interface is a contract which tells the compiler
that a class that implements it implements a set of
method signature which perform certain actions.That's right, but my idea is not to change the interface, but to change the external class, making it implements the existing interface.
If you overlay an interface on someone else's class,
the signature match (if there is one) could happen by
coincidence. There's no guarantee that a method with
a signature that matches one in your interface
actually has the same function.I didn't say that an external class should be viewed as an interface without a specific implementation of this interface for the external class. But, instead of making a new class extending the first and implementing the interface, just define a specific implementation of the interface for this class, as if it was make at class declaration.