public class  Example5_1{
    public static void main(String args[]){
        Son son=new Son();
        Grandson grandson=new Grandson();
        son.setWeight(62);
        son.setHand("一双大手");
        grandson.setWeight(29);
        grandson.setHand("一双小脚");
        System.out.println("儿子体重:"+son.getWeight());
        System.out.println("孙子的体重:"+grandson.getWeight());
        System.out.println("儿子的手:"+son.getHand());
        System.out.println("孙子的手:"+grandson.getHand());
        System.out.println("孙子的脚:"+grandson.getFoot());
    }
}
帮忙看看  为什么有错误？