在下列E类中【代码】输出结果是_____.import java.awt.*;import java.awt.event.*;public class E implements Runnable {StringBuffer buffer=new StringBuffer();Thread t1,t2;E() { t1=new Thread(this);t2=new Thread(this);}public synchronized void addChar(char c) {if(Thread.currentThread()==t1) {while(buffer.length()==0) {try{ wait();}catch(Exception e){}}buffer.append(c);}if(Thread.currentThread()==t2) {buffer.append(c);notifyAll();}}public static void main(String s[]) {E hello=new E();hello.t1.start();hello.t2.start();while(hello.t1.isAlive()||hello.t2.isAlive()){}System.out.println(hello.buffer); //【代码】}public void run() {if(Thread.currentThread()==t1)addChar('A') ;if(Thread.currentThread()==t2)addChar('B') ;}}

A. BA
B. A
C. B
D. AB