Angular 2 @Injectable() vs. @Inject() ?

Why @Injectable ()?

@Injectable () marks a class as available to an injector for instantiation. An injector reports an error when trying to instantiate a class that is not marked as @Injectable ().

Injectors are also responsible for instantiating components. At the run-time the injectors can read class metadata in the JavaScript code and use the constructor parameter type information to determine what things to inject.

Example as,

import { Injectable, InjectionToken } from '@angular/core';
import { Http, Response } from '@angular/http';

@Injectable()
export class UserService {
    constructor(private _http: Http) {
    }

    getAPIUsers(apiUrl) {
        return this._http.get(apiUrl).map((data: Response) => data.json());
    }
}

Why @Inject()?

Angular 2 @Inject() is a special technique for letting Angular know that a parameter must be injected.

Example as,

import { Inject} from '@angular/core';
import { Http, Response } from '@angular/http';

class UserService {
    users: Array<any>;

    constructor( @Inject(Http) _http: Http) {       
    }
}

Angular2 - Related Concepts

When use @Inject()?	When Use @Injectable ()?	@Injectable() vs. @Inject() ?
How to use Dependency Injection (DI) correctly in Angular 2?	Dependency Injection (DI) in Angular 2?

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