class Waiting implements Runnable { boolean flag = false; public synchronized void run() { if (flag) { flag = false; System.out.print("1 "); try { this.wait(); } catch (Exception e) { } System.out.print("2 "); } else { flag = true; System.out.print("3 "); try { Thread.sleep(2000); } catch (Exception e) { } System.out.print("4 "); notify(); } } public static void main(String [] args) { Waiting w = new Waiting(); new Thread(w).start(); new Thread(w).start (); } } 以下哪两项是正确的?()
A. 代码输出 1 3 4
B. 代码输出 3 4 1
C. 代码输出 1 2 3 4
D. 代码不会完成