Interfaces are only at compile time. This allows only you to check that the expected data received follows a particular structure. For this you can cast your content to this interface: this.http.get(‘…’) .map(res => <Product[]>res.json()); See these questions: How do I cast a JSON object to a typescript class How to get Date object from … Read more
The static keyword in the above example is redundant (a nested interface is automatically “static”) and can be removed with no effect on semantics; I would recommend it be removed. The same goes for “public” on interface methods and “public final” on interface fields – the modifiers are redundant and just add clutter to the … Read more
Consider just using composition instead of trying to simulate Multiple Inheritance. You can use Interfaces to define what classes make up the composition, eg: ISteerable implies a property of type SteeringWheel, IBrakable implies a property of type BrakePedal, etc. Once you’ve done that, you could use the Extension Methods feature added to C# 3.0 to … Read more
The entire point of interfaces is to give you the flexibility to have your class be forced to implement multiple interfaces, but still not allow multiple inheritance. The issues with inheriting from multiple classes are many and varied and the wikipedia page on it sums them up pretty well. Interfaces are a compromise. Most of … Read more
Though many of the other answers are correct at the semantic level, I find it interesting to also approach these sorts of questions from the implementation details level. An interface can be thought of as a collection of slots, which contain methods. When a class implements an interface, the class is required to tell the … Read more
An abstract class is a class which cannot be instantiated. An abstract class is used by creating an inheriting subclass that can be instantiated. An abstract class does a few things for the inheriting subclass: Define methods which can be used by the inheriting subclass. Define abstract methods which the inheriting subclass must implement. Provide … Read more
If a type implements two interfaces, and each interface define a method that has identical signature, then in effect there is only one method, and they are not distinguishable. If, say, the two methods have conflicting return types, then it will be a compilation error. This is the general rule of inheritance, method overriding, hiding, … Read more
The JLS makes this clear: It is permitted, but discouraged as a matter of style, to redundantly specify the public and/or abstract modifier for a method declared in an interface.
No one has really explained in plain terms how interfaces are useful, so I’m going to give it a shot (and steal an idea from Shamim’s answer a bit). Lets take the idea of a pizza ordering service. You can have multiple types of pizzas and a common action for each pizza is preparing the … Read more
From the Java interface design FAQ by Philip Shaw: Interface variables are static because Java interfaces cannot be instantiated in their own right; the value of the variable must be assigned in a static context in which no instance exists. The final modifier ensures the value assigned to the interface variable is a true constant … Read more