多线程面试题一道，请写出输出结果

 

public class ThreadRun extends Thread{
	
	public static void main(String agrs[]) throws Exception {
		
		ThreadRun tr = new ThreadRun();
		System.out.print("b");
		tr.start();
		System.out.print("c");
		tr.join();
		System.out.print("d");
	}
	
	public void run() {
		System.out.print("a");
	}

}