In Dart, interfaces are not explicitly declared like in some other languages. Instead, you define an interface by creating an abstract class with abstract methods. Let's see how we can code an interface in Dart using an example:
<pre><code class="lang-dart">// Define an interface for a shape
abstract class Shape {
 // Abstract method to calculate area
 double calculateArea();

 // Abstract method to calculate perimeter
 double calculatePerimeter();
}
</code></pre>
In this example, we've defined an interface called <code>Shape</code> using an abstract class.
The <code>Shape</code> interface declares two abstract methods: <code>calculateArea()</code> and <code>calculatePerimeter()</code>.
Any class that wants to be considered a shape must implement these methods.

In Dart, interfaces are not explicitly declared like in some other languages. Instead, you define an interface by creating an abstract class with abstract methods. Let's see how we can code an interface in Dart using an example:

```dart
// Define an interface for a shape
abstract class Shape {
  // Abstract method to calculate area
  double calculateArea();
  
  // Abstract method to calculate perimeter
  double calculatePerimeter();
}
```

In this example, we've defined an interface called `Shape` using an abstract class.

The `Shape` interface declares two abstract methods: `calculateArea()` and `calculatePerimeter()`.

Any class that wants to be considered a shape must implement these methods.

Dart Interfaces: Coding an Interface in Dart