Implicit interfaces

Every class implicitly defines an interface containing all the instancemembers of the class and of any interfaces it implements. If you want tocreate a class A that supports class B’s API without inheriting B’simplementation, class A should implement the B interface.

A class implements one or more interfaces by declaring them in animplements clause and then providing the APIs required by theinterfaces. For example:

// A person. The implicit interface contains greet().
class Person {
  // In the interface, but visible only in this library.
  final _name;
  // Not in the interface, since this is a constructor.
  Person(this._name);
  // In the interface.
  String greet(String who) => 'Hello, $who. I am $_name.';
}
// An implementation of the Person interface.
class Impostor implements Person {
  get _name => '';
  String greet(String who) => 'Hi $who. Do you know who I am?';
}
String greetBob(Person person) => person.greet('Bob');
void main() {
  print(greetBob(Person('Kathy')));
  print(greetBob(Impostor()));
}

Here’s an example of specifying that a class implements multipleinterfaces:

class Point implements Comparable, Location {...}