是我面试的时候遇到的问题，线程问题，求解

Question

public class Program {     public  static Tuser  user = new Tuser();     public static void main(String[] args) throws InterruptedException {         new Thread(                 new Runnable(){                     public void run(){                         while(true){                             String s = get();                             if (user.getUsername().equals("hehe")) {                                 System.out.println("成功");                                 //break;                             }                         }                     }                 }         ).start();         Thread.sleep(1000);         new Thread(new Runnable(){             @Override             public void run(){                 user.setUsername("hehe");                 user=null;             }         }).start();     }     public static synchronized   String get(){         return user.getUsername();     } }三个渐进式问题： 1.执行后什么结果 2 为什么  3 去掉get方法的synchronized会怎么样？