使用Runnable接口创建并启动两个线程一个线程输出1-50的数字另一个线程输出A-Z的大写和小写字母。2、在程序的main方法中先输出mainbegins分别创建和启动这两个线程然后输出mainends观察结果。

代码如下：

public class ThreadDemo implements Runnable {
    private int type; // 1表示输出数字，2表示输出字母
    private static Object lock = new Object();
    
    public ThreadDemo(int type) {
        this.type = type;
    }
    
    @Override
    public void run() {
        synchronized (lock) {
            if (type == 1) {
                for (int i = 1; i <= 50; i++) {
                    System.out.print(i + " ");
                }
            } else {
                for (char c = 'A'; c <= 'Z'; c++) {
                    System.out.print(c + " ");
                }
                System.out.println();
                for (char c = 'a'; c <= 'z'; c++) {
                    System.out.print(c + " ");
                }
            }
            System.out.println();
        }
    }
    
    public static void main(String[] args) {
        System.out.println("main begins,");
        Thread t1 = new Thread(new ThreadDemo(1));
        Thread t2 = new Thread(new ThreadDemo(2));
        t1.start();
        t2.start();
        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("main ends.");
    }
}

输出结果：

main begins,
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
a b c d e f g h i j k l m n o p q r s t u v w x y z 
main ends.

可以看到，先输出了"main begins,"，然后依次输出了数字和字母，并换行。最后输出了"main ends."。两个线程的输出顺序不一定完全一致，但是数字和字母的输出是交替的