Java学习

博主： Keith
发布时间：2022 年 11 月 30 日
280 次浏览
3030字数
分类：默认分类

**# **Java复习

## 第一部分

```
/**
  * @author me
  * @since time
  */
 package Study;
 
 import java.util.Scanner;
 
 public class Main {
     public static void main(String[] args) {
         Scanner scanner = new Scanner(System.in);
         int a = scanner.nextInt();
         int b = scanner.nextInt();
         System.out.println(a + b);
         int c,d;
         final int e = 666;
         final int f;
 //        e = 2;
         f = 666;
         short g = (short) f;
         if(a> 0){
             b = 1;
         }
         switch (a){
             case 1:
                 System.out.println(a);
                 break;
             case 2:
                 System.out.println(f);
                 break;
             default:
                 System.out.println(e);
         }
         for (int i = 0;i <10; i ++){
 
         }
         int i = 0;
         while (i < 10){
             i ++;
             if (i == 1) continue;
             break;
         }
     }
 }
 
```

```

#创建数据库
 
 create database if not exists sqlpr default charset utf8 collate utf8_general_ci;
 
 # 学生表 Student：
 
 create table Student(
 
 SId varchar(10) ,
 
 Sname varchar(10),
 
 Sage datetime,
 
 Ssex varchar(10));
 
 insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
 
 insert into Student values('02' , '钱电' , '1990-12-21' , '男');
 
 insert into Student values('03' , '孙风' , '1990-05-20' , '男');
 
 insert into Student values('04' , '李云' , '1990-08-06' , '男');
 
 insert into Student values('05' , '周梅' , '1991-12-01' , '女');
 
 insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
 
 insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
 
 insert into Student values('09' , '张三' , '2017-12-20' , '女');
 
 insert into Student values('10' , '李四' , '2017-12-25' , '女');
 
 insert into Student values('11' , '李四' , '2017-12-30' , '女');
 
 insert into Student values('12' , '赵六' , '2017-01-01' , '女');
 
 insert into Student values('13' , '孙七' , '2018-01-01' , '女');
 
 # 课程表 Course
 
 create table Course(
 
 CId varchar(10),
 
 Cname nvarchar(10),
 
 TId varchar(10)); 
 
 insert into Course values('01' , '语文' , '02'); 
 
 insert into Course values('02' , '数学' , '01'); 
 
 insert into Course values('03' , '英语' , '03');
 
 # 教师表 Teacher
 
 create table Teacher(
 
 TId varchar(10),
 
 Tname varchar(10)); 
 
 insert into Teacher values('01' , '张三');
 
 insert into Teacher values('02' , '李四'); 
 
 insert into Teacher values('03' , '王五');
 
 # 成绩表 SC
 
 create table SC(
 
 SId varchar(10),
 
 CId varchar(10),
 
 score decimal(18,1)); 
 
 insert into SC values('01' , '01' , 80); 
 
 insert into SC values('01' , '02' , 90); 
 
 insert into SC values('01' , '03' , 99); 
 
 insert into SC values('02' , '01' , 70); 
 
 insert into SC values('02' , '02' , 60); 
 
 insert into SC values('02' , '03' , 80); 
 
 insert into SC values('03' , '01' , 80); 
 
 insert into SC values('03' , '02' , 80); 
 
 insert into SC values('03' , '03' , 80); 
 
 insert into SC values('04' , '01' , 50); 
 
 insert into SC values('04' , '02' , 30); 
 
 insert into SC values('04' , '03' , 20); 
 
 insert into SC values('05' , '01' , 76); 
 
 insert into SC values('05' , '02' , 87); 
 
 insert into SC values('06' , '01' , 31); 
 
 insert into SC values('06' , '03' , 34); 
 
 insert into SC values('07' , '02' , 89); 
 
 insert into SC values('07' , '03' , 98);
```

```

select * 
 from student a inner join sc b 
 on a.sid = b.sid 
 inner join sc c 
 on a.sid = c.sid and b.cid = 01 and c.cid = 02
 where b.score > c.score;
 
 select * 
 from sc a inner join sc b 
 on a.sid = b.sid 
 where a.cid = 01 and b.cid = 02;
 
 select * 
 from 
 (select * from sc where cid = 01) a inner join 
 (select * from sc where cid = 02) b 
 on a.sid = b.sid;
 
 select *
 from sc a left join sc b 
 on a.sid = b.sid and b.cid = '02'
 where a.cid = '01';
 
 select * 
 from sc 
 where sid not in (select sid from sc where cid = '01') and cid = 02;
 
 select a.sid,a.sname,avg_score 
 from student as a 
 inner join (select sid,AVG(score) as avg_score 
 from sc 
 group by sid 
 having avg_score > 60) as b 
 on a.sid = b.sid;
 
 select b.* 
 from (select sid from sc group by sid) as a 
 left join student as b 
 on a.sid = b.sid;
 
 select a.sid,a.sname,b.ct,b.sum_score 
 from student as a 
 left join (select sid,count(cid) as ct,sum(score) as sum_score 
 from sc 
 group by sid) as b 
 on a.sid = b.sid;
 
 #wrong
 select a.sid,a.sname,count(b.cid) as ct,sum(b.score) as sum_score 
 from student as a 
 left join sc as b 
 on a.sid = b.sid 
 group by a.sid;
 
 select * 
 from student 
 where sid in (select sid from sc);
 
 
 select count(*) 
 from teacher 
 where teacher.Tname like '李%';
 
 #important
 SELECT a.*
 FROM Student a left join SC b on a.sid=b.sid
 left join Course c on b.cid=c.cid
 left join Teacher d on c.tid=d.tid
 WHERE d.tname='张三'
 
 
```

![](https://pdai.tech/images/java_collections_overview.png)

```
Thread
     thread.start();
 thread.stop();
 thread.sleep();
 thread.interrupt();
 isInterrupted();
 yield();
 join();
 synchronized：wait()、notify()、notifyAll()
 
 
```

```
//1. 通过DriverManager来获得数据库连接
 try (Connection connection = DriverManager.getConnection("连接URL","用户名","密码");
      //2. 创建一个用于执行SQL的Statement对象
      Statement statement = connection.createStatement()){   //注意前两步都放在try()中，因为在最后需要释放资源！
     //3. 执行SQL语句，并得到结果集
     ResultSet set = statement.executeQuery("select * from 表名");
     //4. 查看结果
     while (set.next()){
         ...
     }
 }catch (SQLException e){
     e.printStackTrace();
 }
 //5. 释放资源，try-with-resource语法会自动帮助我们close
```

最后修改：2023 年 02 月 08 日

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Java学习

Keith • 2022 年 11 月 30 日

**# **Java复习

## 第一部分

```

![](https://pdai.tech/images/java_collections_overview.png)

```
Thread
     thread.start();
 thread.stop();
 thread.sleep();
 thread.interrupt();
 isInterrupted();
 yield();
 join();
 synchronized：wait()、notify()、notifyAll()
 
 
```