老师请问为什么会有包头不包尾这种设定啊？

老师，我这个代码跟视频一样的可是为什么这结果会报错呢

package cn.sxt.game;

import javax.swing.JFrame;
/**
 * 飞机游戏的主窗口
 * @author 高毅
 *
 */
public class MyGameFrame extends JFrame{
	/**
	 * 初始化窗口
	 */
	public void launchFrame(){
		this.setTitle("尚学堂学员，程序员作品");
		this.setVisible(true);  //设置可见
		this.setSize(500, 500);  //设置窗口大小
		this.setLocation(300,300);  //窗口位置
		
		this.addWindowListener(new WindowAdapter() {
			//设置窗口关闭
			@Override
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
		});
	}
	
	public static void main(String[] args) {
		MyGameFrame f = new MyGameFrame();
		f.launchFrame();
	}
}

报错提示是：The method addWindowListener(WindowListener) in the type Window is not applicable for the arguments (new WindowAdapter(){})

WindowAdapter cannot be resolved to a type

WindowEvent cannot be resolved to a type

对呀，我看出来了，但是我跟视频操作是一样得啊？我主要没用MySQL里的sql语句创建表，我用的是pycharm里得python代码操作得创建表，正常这个Django应该直接创建好，我去哪里找你说的这个呢？现在主要我不知道去哪里解决这个问题？（顺带说我用sqlient3操作是可以得），问题肯定在MySQL，我就是不知道怎么去操作？

老师，这里sql注入的句子 应该会报错吧 为啥能执行呢 难道--是注释符号吗

打出能1000之内能被5整除的数，且每3个数一行。

public class TestWhile03 {

public static void main(String[] args) {

int i = 1;

while(i<=1000) {

if(i%5==0) {

System.out.print(i+"\t");

}if(i%15==0) {

System.out.println();

}

}

}

}

老师我这个哪错了？一直在循环没结果啊。

from django.db import models

# Create your models here.
class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField()

上面是orm类

下面是python manage.py makemigrations mosel_app创建得0001

# Generated by Django 2.2.6 on 2019-10-25 02:46

from django.db import migrations, models


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Question',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('question_text', models.CharField(max_length=200)),
                ('pub_date', models.DateTimeField()),
            ],
        ),
    ]

但是在cmd运行python manage.py migrate  出现下面错误

Operations to perform:

  Apply all migrations: admin, auth, contenttypes, model_app, sessions

Running migrations:

Traceback (most recent call last):

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 82, in _execute

    return self.cursor.execute(sql)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute

    return self.cursor.execute(query, args)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\cursors.py", line 209, in execute

    res = self._query(query)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\cursors.py", line 315, in _query

    db.query(q)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\connections.py", line 226, in query

    _mysql.connection.query(self, query)

MySQLdb._exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(6) NOT NULL)' at line 1")

The above exception was the direct cause of the following exception:

Traceback (most recent call last):

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\migrations\recorder.py", line 67, in ensure_schema

    editor.create_model(self.Migration)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\base\schema.py", line 307, in create_model

    self.execute(sql, params or None)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\base\schema.py", line 137, in execute

    cursor.execute(sql, params)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 99, in execute

    return super().execute(sql, params)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 67, in execute

    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 76, in _execute_with_wrappers

    return executor(sql, params, many, context)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 84, in _execute

    return self.cursor.execute(sql, params)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\utils.py", line 89, in __exit__

    raise dj_exc_value.with_traceback(traceback) from exc_value

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\utils.py", line 82, in _execute

    return self.cursor.execute(sql)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute

    return self.cursor.execute(query, args)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\cursors.py", line 209, in execute

    res = self._query(query)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\cursors.py", line 315, in _query

    db.query(q)

  File "D:\python_virtualEnv\django_env\lib\site-packages\MySQLdb\connections.py", line 226, in query

    _mysql.connection.query(self, query)

django.db.utils.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(6) NOT NULL)' at line 1")

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File "manage.py", line 21, in <module>

    main()

  File "manage.py", line 17, in main

    execute_from_command_line(sys.argv)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line

    utility.execute()

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\__init__.py", line 375, in execute

    self.fetch_command(subcommand).run_from_argv(self.argv)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\base.py", line 323, in run_from_argv

    self.execute(*args, **cmd_options)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\base.py", line 364, in execute

    output = self.handle(*args, **options)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\base.py", line 83, in wrapped

    res = handle_func(*args, **kwargs)

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\core\management\commands\migrate.py", line 234, in handle

    fake_initial=fake_initial,

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\migrations\executor.py", line 91, in migrate

    self.recorder.ensure_schema()

  File "D:\python_virtualEnv\django_env\lib\site-packages\django\db\migrations\recorder.py", line 69, in ensure_schema

    raise MigrationSchemaMissing("Unable to create the django_migrations table (%s)" % exc)

django.db.migrations.exceptions.MigrationSchemaMissing: Unable to create the django_migrations table ((1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(6) NOT NULL)' at line 1"))

提示我一个语法错误，什么NOT NULL，这是什么意思？？？

第31行为什么报错啊，这个怎么理解呢，好急

 第10行和第21行为什么报错啊，代码和教学视频一样的说。

f1 = Frame(root).pack()
f2 = Frame(root).pack()

老师，为什么代码写成这样是水平排列的，不是默认垂直的吗？

public class MyThread4 implements Runnable{
	@Override
	public void run() {
		for(int i=0;i<10;i++) {
			System.out.println("i="+i);
		}
	}
}

public class TestStop {
	public static void main(String[] args) {
		MyThread4 my=new MyThread4();
		Thread t=new Thread(my);
		t.start();//启动循环
		//主线程中的循环
		for(int i=0;i<10;i++) {
			if(i==3) {
				t.stop();//已过时，不建议使用
			}
			System.out.println(Thread.currentThread().getName()+"-----"+i);
		}
	}
}

运行结果：

问题：为什么有的i=0与main-----3在同一行？

i=0与main-----3中间有的隔一行？

有的打印两次i=0，且与main-----3在同一行？

老师麻烦看下这是什么问题，我百度了半天，也没解决好

这个视频中的第二个例子。说将connect的static修饰去掉后。Dao类中的增删改查，就需要创建4个连接对象，增加服务器的压力。

那我在Dao中设一个连接对象为成员变量。然后增删改查都用这个成员变量不就行了么？

老师前面的视频怎么看不了了。。。。。。。。。。

老师，我有几个问题。请教一下

1. 自动增长约束，是必须配合主键一起使用吗？

2. 默认值约束和自动增长约束的删除方法一样，那如果，一个字段有默认值语句，又有自动增长语句，输入删除语句之后，就会都删除了吗？有没有单独分开删除的办法？
   

老师，主键约束，只能一次性全部删除吗？不能分开删除吗？