Clock类的代码：

public class Clock {

Display hour=new Display(24);
Display minute=new Display(60);
Display second=new Display(60);

public Clock(int a, int b, int c){
    hour.setvalue(a);
    minute.setvalue(b);
    second.setvalue(c);
}
public void tick(){
    
        second.increase();
        if(second.getvalue()==0){
            minute.increase();
            if(minute.getvalue()==0){
                hour.increase();
            }
        }
    }

public String toString(){
    return String.format("%02d:%02d:%02d\n",hour.getvalue(),minute.getvalue(),second.getvalue());
}

Display类部分的代码：
public class Display {

private int value=0;
private int limit=0;

public Display(int limit){
    this.limit=limit;
}
public void setvalue(int value){
    this.value=value;
}

public void increase(){
    value++;
    if(value==limit){
        value=0;
    }
}

public int getvalue(){
    return value;
}String.format("%02d:%02d:%02d\n",hour.getvalue(),minute.getvalue(),second.getvalue());
}