// declaring an interface
public interface MyInterface
   {
   // just the signature, no body, implied instance and public.
   int aMethod();
    // ...
   }

// ---------------

// declaring a class that implements some interfaces
public class MyClass implements MyInterface, AnotherInterface
   {

   // with body, or else declared abstract. Must be explicitly declared public.
   public int aMethod()
      {
      return 0;
      }
   // ...
   }

// ---------------

// class reference
public static MyClass mc = new MyClass();

// interface reference
public static MyInterface mi= new MyClass();

// you CANNOT!!! say
public static MyInterface mi = new MyInterface();