03_java基础（八）之static关键字与代码块

2021.static关键字

　　/**
* static关键字
* 1.用static修饰后的方法,称为静态方法.
* 2.静态的方法特点,可以使用类名.方法名称调用方法
* 3.静态方法只能调用静态方法/字段,非静态方法,既可以调用静态方法/字段,也可以调用非静态方法/字段
* 4.被static 修饰后的字段是共享的
*/

　　堆栈简单分析:

　　代码:

 1 package com.day01.station.staticDemo;
 2 
 3 /**
 4  * Created by Administrator on 2018/3/23.
 5  *
 6  * 类:  方法   (普通方法   构造方法)
 7  *      字段/属性
 8  *      代码块
 9  */
10 public class StaticObj {
11     private  String name;
12     private  Integer age;
13     private static String conuntry;
14 
15 
16     /**
17      * static关键字
18      * 1.用static修饰后的方法,称为静态方法.
19      * 2.静态的方法特点,可以使用 类名.方法名称 调用方法
20      * 3.静态方法只能调用静态方法/字段,非静态方法,既可以调用静态方法/字段,也可以调用非静态方法/字段
21      * 4.被static 修饰后的字段是共享的
22      */
23     public static void say(){//修饰的是放方法
24         //System.out.println("-----我是一个方法---------"+name);
25         say3();
26     }
27 
28     public  void say2(){
29         System.out.println("-----我是一个方法2---------"+name+age);
30         say();
31     }
32 
33     public static void say3(){
34         System.out.println("-----我是一个方法3---------");
35     }
36 
37     public String getName() {
38         return name;
39     }
40 
41     public void setName(String name) {
42         this.name = name;
43     }
44 
45     public Integer getAge() {
46         return age;
47     }
48 
49     public void setAge(Integer age) {
50         this.age = age;
51     }
52 
53     public  String getConuntry() {
54         return conuntry;
55     }
56 
57     public  void setConuntry(String conuntry) {
58         StaticObj.conuntry = conuntry;
59     }
60 }

View Code

　　测试

 1 package com.day01.station.staticDemo;
 2 
 3 import org.junit.Test;
 4 
 5 /**
 6  * Created by Administrator on 2018/3/23.
 7  */
 8 public class TestStaticObj {
 9     /**
10      * 测试目的:  验证加了static修饰的字段只用一份,是共享的
11      *  创建两个对象  第一个设置国家为中国   第一个设置国家为美国,如果后面的可以覆盖前面的,那么确实是共享的
12      */
13     @Test
14     public void test3(){
15        // 创建两个对象
16         StaticObj staticObj1 = new StaticObj();
17         StaticObj staticObj2 = new StaticObj();
18 
19         staticObj1.setConuntry("中国");
20 
21 
22         staticObj2.setConuntry("美国");
23         String conuntry2 = staticObj2.getConuntry();
24         System.out.println("conuntry2= "+conuntry2);
25 
26 
27 
28         String conuntry1 = staticObj1.getConuntry();
29         System.out.println("conuntry1= "+conuntry1);
30 
31        // System.out.println(" staticObj1= "+staticObj1);
32       //  System.out.println(" staticObj2= "+staticObj2);
33     }
34     @Test
35     public void test2(){
36        StaticObj.say();
37     }
38     @Test
39     public void test(){
40         //以前
41         StaticObj staticObj = new StaticObj();
42         staticObj.say();
43 
44 
45     }
46 }

View Code

22.构造代码块与静态代码块

　　代码:

 1 package com.day01.station.model;
 2 
 3 /**
 4  * Created by lidongping on 2018/5/2.
 5  */
 6 public class LoginUser2 {
 7     private Integer id;
 8     private String userName;
 9 
10     /**
11      * 静态代码块  作用:初始化对象
12      * 1.只执行一次,不论创建多少个对象
13      */
14     static {
15         System.out.println("------我是静态代码块-----");
16     }
17 
18     /**
19      * 构造代码块
20      * 1.每次创建对象都执行一次
21      * 2.可以有多个构造代码块,但是生产上一般只有一个
22      */
23     {
24         System.out.println("-------我是构造代码块1------");
25     }
26 
27     /**
28      * 构造方法
29      */
30     public LoginUser2() {
31         System.out.println("-------我是构造方法-----");
32     }
33 
34     public Integer getId() {
35         return id;
36     }
37 
38     public void setId(Integer id) {
39         this.id = id;
40     }
41 
42     public String getUserName() {
43         return userName;
44     }
45 
46     public void setUserName(String userName) {
47         this.userName = userName;
48     }
49 }

代码

　　测试代码

 1 package com.day01.station.testDao;
 2 
 3 import com.day01.station.model.LoginUser2;
 4 import org.junit.Test;
 5 
 6 /**
 7  * Created by lidongping on 2018/5/2.
 8  */
 9 public class TestLoginUser2 {
10     //测试构造代码块
11     @Test
12     public void  test(){
13         LoginUser2 loginUser2 = new LoginUser2();
14         System.out.println("loginUser2="+loginUser2);
15 
16         LoginUser2 loginUser3 = new LoginUser2();
17         System.out.println("loginUser2="+loginUser3);
18     }
19 }

测试

23.接口简单使用

接口

 1 package com.day01.station.dao;
 2 
 3 import com.day01.station.model.Product;
 4 
 5 public interface IProductDao {
 6     //增
 7     public void save(String productName, int salePrice);
 8     //删
 9     public void delete(int id);
10     //改
11     public void update(int id,int salePrice,int costPrice);
12     //查
13     public Product query(int id);
14 }

接口

　　实现

  1 package com.day01.station.dao.impl;
  2 
  3 import com.day01.station.dao.IProductDao;
  4 import com.day01.station.model.Product;
  5 
  6 import java.sql.Connection;
  7 import java.sql.DriverManager;
  8 import java.sql.PreparedStatement;
  9 import java.sql.ResultSet;
 10 
 11 
 12 public class ProductDao implements IProductDao {
 13     @Override
 14     public void save(String productName, int salePrice) {
 15         System.out.println("--------我是增加方法---------");
 16         System.out.println(" productName = " + productName + " , salePrice =" + salePrice);
 17         try {
 18             //1. 加载
 19             Class.forName("com.mysql.jdbc.Driver");
 20             // * 2. 连接
 21             Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test_web", "root", "admin");
 22             // PreparedStatement prepareStatement(String sql)
 23             // 创建一个 PreparedStatement 对象来将参数化的 SQL 语句发送到数据库。
 24             String sql = "INSERT INTO product (product_name,sale_price) VALUES (?,?)";
 25             //3.创建 预编译语句
 26             PreparedStatement preparedStatement = connection.prepareStatement(sql);
 27             // void setString(int parameterIndex, String x)将指定参数设置为给定 Java String 值。
 28             preparedStatement.setString(1, productName);
 29             preparedStatement.setInt(2, salePrice);
 30             //添加参数
 31             //preparedStatement.set
 32             //4.执行
 33             preparedStatement.executeUpdate();//重要提醒 不需要传入sql语句
 34             //5.释放资源
 35             preparedStatement.close();
 36             connection.close();
 37 
 38 
 39         } catch (Exception e) {
 40             e.printStackTrace();
 41         }
 42     }
 43 
 44     @Override
 45     public void delete(int id) {
 46         System.out.println(" --------我是删除方法--------- ");
 47         System.out.println("---id=" + id);
 48 
 49         try {
 50             //1.加载
 51             Class.forName("com.mysql.jdbc.Driver");
 52             //2.连接
 53             Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/station_demo", "root", "admin");
 54             //3.创建 预 编译语句
 55             String sql = "DELETE FROM product WHERE id=?";
 56             PreparedStatement preparedStatement = connection.prepareStatement(sql);
 57             //设定参数
 58             preparedStatement.setInt(1, id);
 59             //4.执行语句
 60             preparedStatement.executeUpdate();
 61             //5.释放资源
 62             preparedStatement.close();
 63             connection.close();
 64 
 65         } catch (Exception e) {
 66             e.printStackTrace();
 67         }
 68     }
 69 
 70     @Override
 71     public void update(int id, int salePrice, int costPrice) {
 72         System.out.println("--------我是修改方法---------");
 73         try {
 74             //1.加载
 75             Class.forName("com.mysql.jdbc.Driver");
 76             //2.连接
 77             Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/station_demo", "root", "admin");
 78             //3.创建编译语句
 79             String sql = "UPDATE product SET sale_price=?,cost_price=? WHERE id= ? ";
 80             PreparedStatement preparedStatement = connection.prepareStatement(sql);
 81             preparedStatement.setInt(1, salePrice);
 82             preparedStatement.setInt(2, costPrice);
 83             preparedStatement.setInt(3, id);
 84             //4.执行语句
 85             preparedStatement.executeUpdate();
 86             //5.释放资源
 87             preparedStatement.close();
 88             connection.close();
 89 
 90         } catch (Exception e) {
 91             e.printStackTrace();
 92         }
 93     }
 94 
 95     @Override
 96     public Product query(int id) {
 97         System.out.println("------我是查询方法----------");
 98         Product product = new Product();//袋子
 99         try {
100             //1.加载
101             Class.forName("com.mysql.jdbc.Driver");
102             //2.连接
103             Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/station_demo", "root", "admin");
104             //3.创建编译语句
105             String sql = "SELECT id,product_name,sale_price FROM product WHERE id=?";
106             PreparedStatement preparedStatement = connection.prepareStatement(sql);
107             preparedStatement.setInt(1, id);
108             //4.执行语句
109             ResultSet resultSet = preparedStatement.executeQuery();
110             //解析结果
111             while (resultSet.next()) {//如果有在执行里面
112                 int id1 = resultSet.getInt("id");
113                 String productName = resultSet.getString("product_name");
114                 int salePrice = resultSet.getInt("sale_price");
115                 //封装  袋子
116                 //装
117                 product.setId(id1);
118                 product.setProductName(productName);
119                 product.setSalePrice(salePrice);
120             }
121             //5.释放资源
122             resultSet.close();
123             preparedStatement.close();
124             connection.close();
125         } catch (Exception e) {
126             e.printStackTrace();
127         }
128         return product;
129     }
130 }

实现

　　测试

 1 package com.day01.station.testDao;
 2 
 3 import com.day01.station.dao.impl.ProductDao;
 4 import org.junit.Test;
 5 
 6 /**
 7  * Created by lidongping on 2018/5/2.
 8  */
 9 public class TestDao {
10     @Test
11     public void test(){
12         //1.创建dao对象
13         ProductDao productDao = new ProductDao();
14         //2.调用dao的方法
15         productDao.save("苹果10",8000);
16 
17     }
18 }

实现

24.业务层实现

　　业务层接口代码

 1 package com.day01.station.service;
 2 
 3 /**
 4  * 课程笔记:http://www.cnblogs.com/newAndHui/category/1153640.html
 5  * 疑问咨询wx:851298348
 6  */
 7 
 8 import com.day01.station.model.Product;
 9 
10 /**
11  * 业务层接口命名规则:   I+模型名称+Service  例如:IProductService
12  */
13 public interface IProductService {
14     //增
15     public void save(Product product);
16     //删   根据id删除
17     public void delete(Integer id);
18     //改
19     public void update(Product product);
20     //查  根据id查询产品
21     public Product query(Integer id);
22 }

View Code

　　业务层实现代码

 1 package com.day01.station.service.impl;
 2 
 3 import com.day01.station.dao.impl.ProductDao;
 4 import com.day01.station.model.Product;
 5 import com.day01.station.service.IProductService;
 6 
 7 /**
 8  * 课程笔记:http://www.cnblogs.com/newAndHui/category/1153640.html
 9  * 疑问咨询wx:851298348
10  */
11 public class ProductService implements IProductService{
12     ProductDao productDao = new ProductDao();
13 
14     @Override
15     public void save(Product product) {
16         //1.创建dao对象
17 
18         //调用持久层保存方法
19         String productName = product.getProductName();
20         Integer salePrice = product.getSalePrice();
21         productDao.save(productName,salePrice);
22 
23     }
24 
25     @Override
26     public void delete(Integer id) {
27         productDao.delete(id);
28     }
29 
30     @Override
31     public void update(Product product) {
32         productDao.update(product.getId(),product.getSalePrice(),product.getCostPrice());
33     }
34 
35     @Override
36     public Product query(Integer id) {
37         Product prduct = productDao.query(id);
38 
39         return prduct;
40     }
41 }

View Code