'''
创建TFTP服务器，进行下载文件的操作，需要使用到TFTP服务器软件
'''
from socket import *  # socket套接字在应用层和传输层之间进行传递数据
import struct  # 进行文件格式组织
from threading import Thread

# 构建向TFTP服务的请求数据包
fileName = 'AOY_8074.jpg'
severIp = '192.168.0.107'
cmdBag = struct.pack('!H12sb5sb',1,fileName.encode(),0,'octet'.encode(),0)
# 定义套接字对象,采用IPV4,UDP协议
udpSock = socket(AF_INET,SOCK_DGRAM)
# 向TFTP服务器发送请求数据包，第一次请求时的端口号是69
udpSock.sendto(cmdBag,(severIp,69))
# 创建一个同名的文件,a:以追加模式打开（必要时可以创建）append;b:表示二进制
f = open(fileName,'ab')
# 创建循环接收TFTP服务器返回的数据包
while True:
    # 接收服务器返回的数据包
    recvData = udpSock.recvfrom(1024)
    # 将返回的数据包中的内容进行转换，分别赋值给操作码，数据块，服务器的随机端口号
    caozuoma,dataBlock = struct.unpack('!HH',recvData[0][:4])
    serverPort = recvData[1][1]
    # 判断操作码为5时，服务器没有下载文件，跳出循环
    if caozuoma == 5:
        print('服务器无此文件……')
        break
    print(f'服务器返回信息,操作码:{caozuoma},块编号:{dataBlock},文件大小:{len(recvData)}')
    # 将接收的数据写入文件
    f.write(recvData[0][4:])
    # 判断文件下载是否完成,当字节数小于516时表示文件最后一次传输
    if len(recvData) < 516:
        print('文件下载完成')
        break
    # 将返回的ACK数据包进行格式组织，操作码4表示ACK的确认码
    ackBag = struct.pack('!HH',4,dataBlock)
    udpSock.sendto(ackBag,(severIp,serverPort))

老师我这个代码运行后，下载的图片只有2个字节。

老师，这里为什么传一个mmid啊？select语句里写的是pid。传mmid能查到吗？

老师，jdbcTemplate返回的int类型的数组，里面的值是什么什么意义呢？

import pygame
from pygame.sprite import Sprite
import time
import random
SCREEN_WIDTH=700
SCREEN_HEIGHT=500
BG_COLOR=pygame.Color(0,0,0)
TEXT_COLOR=pygame.Color(255,0,0)
class BaseItem(Sprite):
    def __init__(self,color,width,height):
        pygame.sprite.Sprite.__init__(self)

class Maingame():
    window=None
    my_tank=None
    enemyTankList=[]
    enemyTankcount=5
    myBulletList=[]
    enemyBulletList=[]
    explodeList=[]
    def createEnemyTank(self):
       top=100

       #循环生成敌方坦克
       for i in range(Maingame.enemyTankcount):

           left=random.randint(0,600)
           speed=random.randint(1,4)

           enemy=Enemytank(left,top,speed)
           Maingame.enemyTankList.append(enemy)
    def blitEnemyTank(self):
        #判断敌方坦克是否活着

        for enemyTank in Maingame.enemyTankList:
            if enemyTank.live:
                enemyTank.displayTank()
                enemyTank.randMove()
                enemyBullet=enemyTank.shot()
                if enemyBullet:
                    Maingame.enemyBulletList.append(enemyBullet)
            else:
                Maingame.enemyTankList.remove(enemyTank)


    def blitMyBullet(self):
        #判断当前子弹是否为活着的状态，如果不是则在列表中删除

        for myBullet in Maingame.myBulletList:
            if myBullet.live:
                myBullet.displayBullet()
                myBullet.move()
                myBullet.myBullet_hit_enemyTank()
            else:
                Maingame.myBulletList.remove(myBullet)
    def blitEnemyBullet(self):
        for enemyBullet in Maingame.enemyBulletList:
            if enemyBullet.live:

                enemyBullet.displayBullet()
                enemyBullet.move()

            else:
                Maingame.enemyBulletList.remove(enemyBullet)




    def  __init__(self):
       pass
    def startgame(self):
        pygame.display.init()
        Maingame.window = pygame.display.set_mode([SCREEN_WIDTH, SCREEN_HEIGHT])
        pygame.display.set_caption("坦克大战1.03")
        Maingame.my_tank=Tank(350,250)
        self.createEnemyTank()
        while True:
            time.sleep(0.02)
            pygame.display.update()
            Maingame.window.fill(BG_COLOR)
            Maingame.window.blit(self.getTextSurface("敌方坦克剩余数量%d"%len(Maingame.enemyTankList)),(10,10))# 后一个位置可接元组
            self.getEvent()
            Maingame.my_tank.displayTank()
            self.blitEnemyTank()
            self.blitMyBullet()
            self.blitEnemyBullet()
            self.blitExplode()
    def blitExplode(self):
        for explode in Maingame.explodeList:
            if explode.live:
                explode.displayExplode()
            else:
                Maingame.explodeList.remove(explode)
            if not Maingame.my_tank.stop:
                Maingame.my_tank.move()

    def endgame(self):
        print("谢谢使用哦")
        exit()
    def getEvent(self):
        eventList=pygame.event.get()
        for event in eventList:
            if event.type == pygame.QUIT:
                self.endgame()
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    Maingame.my_tank.direction="L"
                    Maingame.my_tank.stop=False
                    #Maingame.my_tank.move()
                    print("坦克向左移动")
                elif event.key == pygame.K_UP:
                    Maingame.my_tank.direction = "U"
                    Maingame.my_tank.stop=False

                    #Maingame.my_tank.move()
                    print("坦克向上移动")
                elif event.key == pygame.K_RIGHT:
                    Maingame.my_tank.direction = "R"
                    Maingame.my_tank.stop = False
                    #Maingame.my_tank.move()
                    print("坦克向右移动")
                elif event.key == pygame.K_DOWN:
                    Maingame.my_tank.direction = "D"
                    Maingame.my_tank.stop = False
                    print("坦克向下移动")
                elif event.key == pygame.K_SPACE:
                    print("发射子弹")
                    #Maingame.my_tank.move()
                    if len(Maingame.myBulletList)<=3:
                        myBullet=Bullet(Maingame.my_tank)
                        Maingame.myBulletList.append(myBullet)

            if event.type == pygame.KEYUP:
                if event.key== pygame.K_UP or event.key==pygame.K_DOWN or event.key==pygame.K_RIGHT or event.key==pygame.K_LEFT:
                    Maingame.my_tank.stop=True

    def getTextSurface(self,text):
        #初始化字体模块
        pygame.font.init()
        font=pygame.font.SysFont("kaiti",18)
        textSurface=font.render(text,True,TEXT_COLOR)
        return textSurface




class Tank(BaseItem):
    def __init__(self,top,left):
        self.images={
            "U":pygame.image.load("imgs/p1tankU.gif"),
            "D": pygame.image.load("imgs/p1tankD.gif"),
            "L": pygame.image.load("imgs/p1tankL.gif"),
            "R": pygame.image.load("imgs/p1tankR.gif")

        }
        self.direction="U"
        self.image=self.images[self.direction]
        self.rect=self.image.get_rect()
        self.rect.left=left
        self.rect.top=top
        self.speed=10
        self.stop = True
        self.live = True

    def move(self):
        if self.direction =="L":
            if self.rect.left>0:
               self.rect.left -= self.speed
        elif self.direction =="U":
            if self.rect.top>0:
               self.rect.top -= self.speed
        elif self.direction =="D":
            if self.rect.top+self.rect.height<SCREEN_HEIGHT:
               self.rect.top += self.speed
        elif self.direction =="R":
            if self.rect.left+self.rect.height<SCREEN_WIDTH:
                self.rect.left += self.speed
    def shot(self):
        return Bullet(self)
    def displayTank(self):
        self.image=self.images[self.direction]
        Maingame.window.blit(self.image,self.rect)
#我方坦克
class Mytank():
    def __init__(self):
        pass
class Enemytank(Tank):
    def __init__(self,left,top,speed):
        super(Enemytank,self).__init__(left,top)
        self.images={"U":pygame.image.load("imgs/enemy1U.gif"),
                     "R": pygame.image.load("imgs/enemy1R.gif"),
                     "L":pygame.image.load("imgs/enemy1L.gif"),
                     "D":pygame.image.load("imgs/enemy1D.gif")
                     }
        self.direction=self.randDirection()
        self.image = self.images[self.direction]
        self.rect=self.image.get_rect()
        self.rect.left=left
        self.rect.top=top
        self.speed=speed
        self.flag=True
        self.step=60



    def randDirection(self):
        num = random.randint(1,4)
        if num==1:
            return "U"
        elif num ==2:
            return "R"
        elif num ==3:
            return  "L"
        elif num==4:
            return "D"
    #敌方坦克随机移动的方法
    def randMove(self):
        if self.step <=0:
            self.direction=self.randDirection()
            self.step=60
        else:
            self.move()
            self.step-=1
    def shot(self):
        num=random.randint(1,100)
        if num <10:
            return Bullet(self)

class Wall():
    def __init__(self):
        pass
    def display(self):
        pass
class Explode():
    #爆炸同tank的位置相同
    def __init__(self,tank):
        self.rect= tank.rect
        self.images=[pygame.image.load("imgs/blast0.gif"),
                     pygame.image.load("imgs/blast1.gif"),
                     pygame.image.load("imgs/blast2.gif"),
                     pygame.image.load("imgs/blast3.gif"),
                     pygame.image.load("imgs/blast4.gif"),

        ]
        self.step=0
        self.image=self.images[self.step]
        self.live=True

    def displayExplode(self):
        if self.step <len(self.images):
            self.image=self.images[self.step]
            self.step+=1
            Maingame.window.blit(self.image,self.rect)
        else:
            self.live=False
            self.step=0

class music():
    def __init__(self):
        pass
    def play(self):
        pass
class Bullet(BaseItem):
    def __init__(self,tank):
        self.image=pygame.image.load("imgs/enemymissile.gif")

        self.direction= tank.direction
        self.rect=self.image.get_rect()
        if self.direction=="U":
            self.rect.left= tank.rect.left+tank.rect.width/2-self.rect.width/2
            self.rect.top = tank.rect.top-self.rect.top
        elif self.direction=="D":
            self.rect.left= tank.rect.left+tank.rect.width/2-self.rect.width/2
            self.rect.top = tank.rect.top+self.rect.top
        elif self.direction=="L":
            self.rect.left= tank.rect.left-tank.rect.width/2-self.rect.width/2
            self.rect.top = tank.rect.top+tank.rect.width/2-self.rect.width/2
        elif self.direction=="R":
            self.rect.left= tank.rect.left+tank.rect.width
            self.rect.top = tank.rect.top+tank.rect.width/2-self.rect.width/2

        self.speed=6
        #增加子弹的状态是否碰到墙壁
        self.live=True

    def displayBullet(self):
        Maingame.window.blit(self.image,self.rect)
    def move(self):
        if self.direction =="U":
            if self.rect.top >0:
                self.rect.top -=self.speed
            else:
                self.live=False
        elif self.direction == "R":
            if self.rect.left+self.rect.width<SCREEN_WIDTH:
                self.rect.left+=self.speed
            else:
                self.live=False
        elif self.direction == "L":
            if self.rect.left>0:
                self.rect.left-=self.speed
            else:
                self.live=False
        elif self.direction == "D":
            if self.rect.top+self.rect.height<SCREEN_HEIGHT:
                self.rect.top+=self.speed
            else:
                self.live=False
    #我方子弹与敌方坦克的碰撞
    def myBullet_hit_enemyTank(self):
        for enemyTank in Maingame.enemyTankList:
            if pygame.sprite.collide_rect(enemyTank,self):
                enemyTank.live=False
                self.live=False
                explode=Explode(enemyTank)
                Maingame.explodeList.append(explode)





if __name__== '__main__':
    Maingame().startgame()
 
 
#老师，请问我这个代码跑的时候为什么会出现我方坦克只能打中对方才能移动的情况呢

关于repeatable read

为什么我把李四设置完隔离等级repeatable read后，张三提交事物后，再用

start transaction；

    select * from account;这两个一起运行查看，发现数据显示也是变化后的呢？难道不能把start transaction再运行一遍？

如果只运行select * from account；查看数据是没有变化的；

老师，这里面的map.entrySet()方法返回的Set<Map.Entry<String,String>>,这个Entry是Map的内部接口，里面的getKey和getValue方法都是抽象方法，没有具体实现类，那怎么能直接调用？

不是说指定放到偏移量中吗，我想放到偏移量2中怎么放

老师，

1. 当链表长度大于8时就会转换为红黑树，这个的前提条件是不是数组长度大于等于64才能转换？

2. 如果链表长度大于8，数组长度小于64，是不是链表不会转换成红黑树，而是数组进行扩容？

3. 如果上面的两个问题是对的话，那激发数组扩容的条件是不是有两个，一个就是当数组被沾满75%，另一个是链表长度大于8（数组长度小于64）

老师，请问 一下这个报错是怎么回事呀，不太明白。是运行次数太多了 还是代码...

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: 

Cannot delete or update a parent row: a foreign key constraint fails (`test`.`employees`, CONSTRAINT `emp_fk` FOREIGN KEY (`dept_id`) REFERENCES `departments` (`department_id`))

老师 我在数据层下写了一个删除数据的代码 然后正常步骤服务层调用数据层方法 -- 测试类再调用服务层方法 

最后报如上的错误 怎么解决啊老师  是因为department_id 这一列是数据库其他表的外键吗 

老师这个返回的这个对象是怎么传到页面中进行判断的呢搞不懂？为什么jsp中就能收到这个data.status==200呢？以及红圈里代码如何理解？

老师，类实例化成对象的过程是编译器将代码编译成 .class文件的过程吗？是不是先有了对象然后才调用构造方法对对象里面的属性进行初始化？类的加载跟类的实例化是不是一个意思？

请问老师，值一样，地址是有可能不一样的吗