public class Lao {
 
 String pifu="黑黑的";

    String yachi;

    public Lao(){

           yachi="白白的";

    }

      String jishu(){
         
           return "会种小麦和大米";
    
      }

      String yule(){

           return "会唱信天游";

      }

}

public class Xiao extends Lao{
 
 public Xiao() {
                          super();

                     this.pifu=super.pifu;
                    
 }

                     String  jishu(){

                          return super.jishu()+"还会种菜";

                    }

                     
                    String yule(){
 
                          return super.yule()+ "还会表演";

                     }
            }

public class Nongmin {

 public static void main(String[] args) {
 
  Lao x=new Lao();

        Xiao y=new Xiao();

        x.jishu();

        x.yule();
       
        y.jishu();

        y.yule();
    
       System.out.println("程序运行结束");
 }

}

老师，麻烦帮我看一下这个程序写的有问题么，为啥运行时直接输出：程序运行结束