在Angular中，如何访问在生命周期中初始化的全局变量？

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

@Injectable({
  providedIn: 'root'
})
export class GlobalService {
  globalVariable: string;

  constructor() { }

  setGlobalVariable(value: string) {
    this.globalVariable = value;
  }

  getGlobalVariable() {
    return this.globalVariable;
  }
}

import { Component, OnInit } from '@angular/core';
import { GlobalService } from './global.service';

@Component({
  selector: 'app-root',
  template: `
    <h1>{{ globalVariable }}</h1>
  `
})
export class AppComponent implements OnInit {
  globalVariable: string;

  constructor(private globalService: GlobalService) { }

  ngOnInit() {
    this.globalService.setGlobalVariable('Hello, world!');
    this.globalVariable = this.globalService.getGlobalVariable();
  }
}