子类

public class testper extends person {
    int grade;
    void study(){
        System.out.println("学习,年级是"+this.grade);
    }
}

测试下继承


public class ss {
public static void main(String[] args){
        testper testper=new testper();
        testper.grade=1;
        testper.name="北京";
        testper.age=10;
        testper.eat();
        testper.introduce();
        testper.study();
    }
}

interface Useb {
   void read();
   void write();
}

wifi接口
public interface WiFi {
    public void open();
    public void close();
}

实现
public class Usebpone  implements Useb,WiFi{
    public  void read() {
        System.out.println("useb  read");
    }
    public  void write() {
        System.out.println("useb  write");
    }
    public void open(){
        System.out.println("wifi  open");
    }
    public void close() {
        System.out.println("wifi  open");
    }
}

测试
public class test {
    public static void main(String agrs[]) {
        Usebpone usbPhone=new Usebpone();
        Useb sab=usbPhone;
        sab.read();
        sab.write();
        WiFi wiFi=usbPhone;
        wiFi.open();
        wiFi.close();
    }
}