angular2 把TypeScript像写java那样面向接口编程 哈哈

import {Component} from 'angular2/core';
import {User} from "./User";
import {UserService} from "./user-service";


@Component({
    selector: 'appTest',template: `
            <ul>
                <li *ngFor="#user of users"><span>{{user.name}}</span>{{user.age}}</li>
            </ul>
    `,providers: [
        UserService
    ]
})

export class App {
    users: User[];
    constructor(private userService: UserService) {
        this.users = userService.getUsers();
    }
}  

/**
 * Created by dell on 2016/9/8.
 */
import {Injectable} from 'angular2/core';
import {Users} from "./user-data";
import {LogHelper} from "./log-help";

@Injectable()
export class UserService {

    getUsers() {
        LogHelper.getInstance().log("get user.");
        return Users;
    }
}

/**
 * Created by dell on 2016/9/9.
 */
import {ILog} from "./ILog";
import {LogImpl1} from "./LogImpl1";
import {LogImpl2} from "./LogImpl2";

export class LogHelper {

    private static loghelper:LogHelper = null;

    private currentTag:number = 0;

    private logobj:ILog;

    private LogHelper() {

    }

    public static getInstance() {

        if (this.loghelper == null) {
            this.loghelper = new LogHelper();
        }
        return this.loghelper;
    }

    public log(info:string){
        if(this.currentTag == 0){
            this.logobj = new LogImpl1();
        }else{
            this.logobj = new LogImpl2();
        }
        this.logobj.info("哈哈" + info)
    }
}

/**
 * Created by dell on 2016/9/9.
 */

export interface ILog{
    info(info: string);
}

/**
 * Created by dell on 2016/9/9.
 */
import {ILog} from "./ILog";

export class LogImpl1 implements ILog{
    public info(info: string){
        console.log(info + ":LogImpl1 ")
    }
}

/**
 * Created by dell on 2016/9/9.
 */
import {ILog} from "./ILog";

export class LogImpl2 implements ILog{
    public info(info: string){
        console.log(info + ":LogImpl2 ")
    }
}