public class AbstractTest {    public static void main(String[] args) {                //一旦Person类抽象了，就不可实例化//        Person p1 = new Person();//        p1.eat();            }}abstract class Creature{    public abstract void breath();}abstract class Person extends Creature{    String name;    int age;        public Person(){            }    public Person(String name,int age){        this.name = name;        this.age = age;    }        //不是抽象方法：//    public void eat(){//        //    }    //抽象方法    public abstract void eat();        public void walk(){        System.out.println("人走路");    }        }class Student extends Person{        public Student(String name,int age){        super(name,age);    }    public Student(){    }        public void eat(){        System.out.println("学生多吃有营养的食物");    }    @Override    public void breath() {        System.out.println("学生应该呼吸新鲜的没有雾霾的空气");    }}