listuser.component.ts

import Component, OnInit from '@angular/core';
import User from 'src/app/user';
import UserService from 'src/app/shared_service/user.service';

@Component(
 selector: 'app-listuser',
 templateUrl: './listuser.component.html',
 styleUrls: ['./listuser.component.css']
)
export class ListuserComponent implements OnInit 
 private users:User;
 _userService: any;
 constructor(private_userService:UserService) 

 ngOnInit() 
 this._userService.getUsers().subscribe((users)=>
 console.log(users);
 this.users=users;
 ,(error)=>
 console.log(error);
 )
 

user.service.ts

import Injectable from '@angular/core';
import Http, Response, Headers, RequestOptions from '@angular/http';
import Observable from 'rxjs';
import 'rxjs/add/operator/map';
import 'rxjs-compat';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

import User from '../user';

@Injectable(
 providedIn: 'root'
)
export class UserService 
 private baseUrl:string="http://localhost:8080/api";
 private headers = new Headers('Content-Type':'application/json');
 private options = new RequestOptions(headers:this.headers);
 _http: any;
 constructor(private_http:Http) 

 getUsers()
 
 return this._http.get(this.baseUrl+'/users',this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 getUser(id:Number)
 
 return this._http.get(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 deleteUser(id:Number)
 
 return this._http.delete(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 createUsers(user:User)
 
 return this._http.post(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 updateUsers(user:User)
 
 return this._http.put(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 errorHandler(error:Response)'SERVER ERROR');
 

after Run this ..the error:
ERROR TypeError: Cannot read property 'getUsers' of undefined
at ListuserComponent.push../src/app/components/listuser/listuser.component.ts.ListuserComponent.ngOnInit (listuser.component.ts:16)
at checkAndUpdateDirectiveInline (core.js:18620)
at checkAndUpdateNodeInline (core.js:19884)
at checkAndUpdateNode (core.js:19846)
at debugCheckAndUpdateNode (core.js:20480)
at debugCheckDirectivesFn (core.js:20440)
at Object.eval [as updateDirectives] (ListuserComponent_Host.ngfactory.js? [sm]:1)
at Object.debugUpdateDirectives [as updateDirectives] (core.js:20432)
at checkAndUpdateView (core.js:19828)
at callViewAction (core.js:20069)

Looks like you have forgotten to add blank space after private and before _userService in your constructor:

constructor(private _userService:UserService) 

you need to add space between private and _userService, so this

constructor(private_userService:UserService) 

should be

constructor(private _userService: UserService) 

There are couple issues in your service class -

1. Space between private and _http
   


2. Remove additional declared instance variable _http: any;
   

Modified code

import Injectable from '@angular/core';
import Http, Response, Headers, RequestOptions from '@angular/http';
import Observable from 'rxjs';
import 'rxjs/add/operator/map';
import 'rxjs-compat';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

import User from './user';

@Injectable(
 providedIn: 'root'
)
export class UserService 
 private baseUrl:string="http://localhost:8080/api";
 private headers = new Headers('Content-Type':'application/json');
 private options = new RequestOptions(headers:this.headers);
 constructor(private _http:Http) 

 getUsers()
 
 return this._http.get(this.baseUrl+'/users',this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 getUser(id:Number)
 
 return this._http.get(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 deleteUser(id:Number)
 
 return this._http.delete(this.baseUrl+'/user/'+id,this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 createUsers(user:User)
 
 return this._http.post(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 updateUsers(user:User)
 
 return this._http.put(this.baseUrl+'/users',JSON.stringify(user), this.options).map((response:Response)=>response.json())
 .catch(this.errorHandler);

 
 errorHandler(error:Response)'SERVER ERROR');