java多线程第三天死锁问题

package com.company.javaThreadTest;

/**
* Created by likailong on 2016/10/24.
*   username=a
username=b
出现死锁
*/
public class DeathLock  implements Runnable
{
public String username;
private Object lock1=new Object();
private Object lock2=new Object();
public void setFlag(String username){
this.username=username;
}
@Override
public void run() {
if(username.equals("a")){
synchronized(lock1){
try {
System.out.println("username=" + username);
Thread.sleep(3000);
}catch (InterruptedException e){
e.printStackTrace();
}
synchronized(lock2){
System.out.println("按照lock1  lock2执行");
}
}
}if(username.equals("b")){
synchronized(lock2){
try {
System.out.println("username=" + username);
Thread.sleep(3000);
}catch (InterruptedException e){
e.printStackTrace();
}
synchronized(lock1){
System.out.println("按照lock2  lock1执行");
}
}
}
}
public static void main(String [] args) throws InterruptedException {
DeathLock deathLock=new DeathLock();
deathLock.setFlag("a");
Thread t=new Thread(deathLock);
t.start();
Thread.sleep(100);
deathLock.setFlag("b");
Thread t2=new Thread(deathLock);
t2.start();
}
}