Javascript 在 Angular 中获取当前 url

我怎么才能得到4号角的当前url呢？我在网上找了很久，但还是找不到解决方案.

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { RouterModule, Router } from '@angular/Router';

import { AppComponent } from './app.component';
import { TestComponent } from './test/test.component';
import { OtherComponent } from './other/other.component';
import { UnitComponent } from './unit/unit.component';

@NgModule ({
  declarations: [
    AppComponent,
    TestComponent,
    OtherComponent,
    UnitComponent
  ],

  imports: [
    BrowserModule,
    RouterModule.forRoot([
        {
            path: 'test',
            component: TestComponent
        },
        {
            path: 'unit',
            component: UnitComponent
        },
        {
            path: 'other',
            component: OtherComponent
        }
    ]),
  ],

  providers: [],
  bootstrap: [AppComponent]
})

export class AppModule { }

app.component.html个

<!-- The content below is only a placeholder and can be replaced -->
<div>
    <h1>Welcome to {{title}}!!</h1>

    <ul>
        <li>
            <a routerLink="/test">Test</a>
        </li>
        <li>
             <a routerLink="/unit">Unit</a>  
        </li>
        <li>
            <a routerLink="/other">Other</a>
        </li>
    </ul>
</div>
<br/>
<router-outlet></router-outlet>

app.component.ts

import { Component} from '@angular/core';

@Component ({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})

export class AppComponent{
    title = 'Angular JS 4';
    arr = ['abcd','xyz','pqrs'];
}

other.component.ts个

import { Component, OnInit } from '@angular/core';
import { Location } from '@angular/common';
import { Router } from '@angular/router';

@Component({
  selector: 'app-other',
  templateUrl: './other.component.html',
  styleUrls: ['./other.component.css']
})

export class OtherComponent implements OnInit {

    public href: string = "";
    url: string = "asdf";

    constructor(private router : Router) {}

    ngOnInit() {
        this.href = this.router.url;
        console.log(this.router.url);
    }
}

test.component.ts

import { Component, OnInit } from '@angular/core';
import { Location } from '@angular/common';
import { Router } from '@angular/router';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})

export class TestComponent implements OnInit {
    route: string;
    currentURL='';

    constructor() { 
        this.currentURL = window.location.href; 
    }

    ngOnInit() { }
}

现在我在点击other链接后发现了控制台问题

ERROR Error: Uncaught (in promise): Error: No provider for Router!