多态之笔记本案例

USB 接口

package com.myc.day05.laptop;

public interface USB {
    void open(); // 开启
    void close(); // 关闭
}

Mouse 类

package com.myc.day05.laptop;

public class Mouse  implements USB{
    @Override
    public void open() {
        System.out.println("鼠标已开启");
    }

    @Override
    public void close() {
        System.out.println("鼠标已关闭");
    }
    public void click(){
        System.out.println("鼠标被点击");
    }
}

KeyBoard 类

package com.myc.day05.laptop;

public class KeyBoard implements USB{


    @Override
    public void open() {
        System.out.println("键盘开启");
    }

    @Override
    public void close() {
        System.out.println("键盘关闭");
    }
    public void type(){
        System.out.println("键盘打字");
    }
}

Laptop 类

package com.myc.day05.laptop;

public class Laptop {
    // 开机
    public void run(){
        System.out.println("笔记运行。。。。");
    }
    // 定义使用usb设备的方法
    public void useUSB(USB usb){
        if (usb != null){
            usb.open();
            // 判断（插入设备的类型）是鼠标还是键盘
            // instanceof 判断是否属于同一种类型
            if (usb instanceof KeyBoard){
                // 将usb类型强制转换为 KeyBoard类型  (向下转型)
                KeyBoard kb = (KeyBoard)usb;
                // 调用 KeyBoard特有的方法
                kb.type();
            }else if (usb instanceof Mouse){
                Mouse mouse = (Mouse)usb;
                mouse.click();
            }
            usb.close();
        }
    }
    // 关机方法
    public void shutdown(){
        System.out.println("关机");
    }
}

测试类

package com.myc.day05.laptop;

public class Test {
    public static void main(String[] args) {
        Laptop laptop = new Laptop();
        laptop.run();
        // 使用鼠标
        Mouse mouse = new Mouse();
        laptop.useUSB(mouse);
        // 使用键盘
        KeyBoard keyBoard = new KeyBoard();
        laptop.useUSB(keyBoard);
        laptop.shutdown();
    }
}

Java操作数据库(JDBC)

package com.myc.day05.JDBC;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;

public class JDBCDemo1 {
    public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jade", "root", "root");
//        String sql = "update account set balance = 20000 where id = 1";
//        String sql = "insert into account values (220 , null )";
        String sql = "delete from account where id = 1";

//        String sql = "update emp set sal = 1800 where empno = 7369";
        Statement statement = conn.createStatement();
        int row = statement.executeUpdate(sql);
        System.out.println("row = "+ row);
        statement.close();
        conn.close();

    }
}

查询

package com.myc.day05.JDBC;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class JDBCDemo2 {
    public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jade", "root", "root");

        String sql = "select * from emp ";

        Statement statement = conn.createStatement();
        ResultSet rs = statement.executeQuery(sql);
//        boolean next = rs.next();
//        System.out.println("next"+ next);
        while (rs.next()){
            int empno = rs.getInt(1);// 通过列名和索引序号都可以获得数据
            String ename = rs.getString(2);

//        int empno = rs.getInt("empno");
//        String ename = rs.getString("ename");

            System.out.println(empno+"   " + ename);

        }


        statement.close();
        conn.close();

    }
}