Interfaces and Classes

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Intro to Interfaces and Classes

Interfaces define contracts that classes can implement. They specify what methods and properties a class must have, without providing the implementation.

interface Flyable {
	fly(): void
}

class Bird implements Flyable {
	fly(): void {
		console.log('Flying!')
	}
}

Implementing Interfaces

When a class implements an interface, it must provide all required members:

interface Drawable {
	draw(): void
}

class Circle implements Drawable {
	draw(): void {
		console.log('Drawing a circle')
	}
}

Multiple Interfaces

A class can implement multiple interfaces:

interface Swimmable {
	swim(): void
}

interface Flyable {
	fly(): void
}

class Duck implements Swimmable, Flyable {
	swim(): void {
		console.log('Swimming')
	}
	fly(): void {
		console.log('Flying')
	}
}

Programming to Abstractions

Use interfaces as types to write flexible code:

function processAnimal(animal: Flyable) {
	animal.fly() // Works with any class that implements Flyable
}

processAnimal(new Bird())
processAnimal(new Duck())

Interfaces enable polymorphism—you can treat different classes the same way if they implement the same interface.

In this exercise, you'll implement interfaces and program to abstractions.