這是一道關於多執行緒的面試題，好久沒有做過這種多執行緒的題了，手有點生，那麼就來敲一敲

package threadDemo;

/*
 * 多執行緒的交叉列印
 */
public class threaddemo1 {
    public static void main(String[] args) {
        num num = new num();
        Thread t1 = new Thread(new thread1(num));
        Thread t2 = new Thread(new thread1(num));
        t1.start();
        t2.start();
    }
}

class
 
 num {
    public int count;
    public num() {
    }

}

class thread1 implements Runnable {
    private final num num;
    public thread1(num num) {
        this.num = num;
    }

    @Override
    public void run() {
            synchronized (num) {
            while (num.count <= 20) {
                for
 
 (int i = 0; i < 5; i++) {
                    System.out.println(Thread.currentThread().getName() + "-"
                            + num.count++);
                }
                num.notify();
                try {
                    num.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
 

                    e.printStackTrace();
                }
            }
        }

    }

}