理解Java对象的交互：时钟显示程序

 1 package clock;
 2 
 3 public class Display {
 4     int value = 0;
 5     int limit = 0;
 6     
 7     Display(int limit) {
 8         this.limit = limit;
 9     }
10 
11     void increase() {
12         ++ value;
13         if(value == limit){
14         value = 0;
15         }
16     }
17     
18     int getvalue() {
19         return value;
20     }
21     
22     public static void main(String[] args) {            //test
23         Display min = new Display(60);
24         for(;;) {
25             min.increase();
26             System.out.println(min.getvalue());
27         }
28     }
29     
30 }

 1 package clock;
 2 
 3 public class Clock {
 4     Display min = new Display(60);
 5     Display hour = new Display(24);
 6     
 7     void start() {
 8         min.increase();
 9         if(min.getvalue()==0) {
10             hour.increase();
11         }
12     }
13     
14     public static void main(String[] args) {
15         Clock clock = new Clock();
16         for(;;) {
17             clock.start();
18             System.out.printf("%02d:%02d\n",clock.hour.getvalue(),clock.min.getvalue());
19         }
20     }
21 
22 }