16. 软件工程-Software Engineering.ass.txt

Hi, I'm Carrie Anne, and welcome to CrashCourse Computer Science!
(｡･∀･)ﾉﾞ嗨，我是 Carrie Anne，欢迎收看计算机科学速成课！

So we've talked a lot about sorting in this series
之前花了很多时间讲排序

and often code to sort a list of numbers might only be ten lines long,
也写了些 10 行左右的排序代码

which is easy enough for a single programmer to write.
对1个程序员来说很容易写

Plus, it's short enough that you don't need any special tools
而且代码很短，不必用专门工具

- you could do it in Notepad.
- 记事本就够了

Really!
真的！

But, a sorting algorithm isn't a program;
但排序算法很少会是独立程序 \N 更可能是大项目的一小部分

it's likely only a small part of a much larger program.
但排序算法很少会是独立程序 \N 更可能是大项目的一小部分

For example, Microsoft Office has roughly 40 millions lines of code.
举个例子，微软的 Office 大约有 4000 万代码

40 MILLION!
4000 万！

That's way too big for any one person to figure out and write!
太多了，一个人不可能做到

To build huge programs like this, programmers use a set of tools and practices.
为了写大型程序，程序员用各种工具和方法

Taken together, these form the discipline of Software Engineering
所有这些形成了"软件工程"学科

- a term coined by engineer Margaret Hamilton,
- 这个词由工程师 Margaret Hamilton 创造

who helped NASA prevent serious problems during the Apollo missions to the moon.
她帮助 NASA 在阿波罗计划中避免了严重问题

She once explained it this way:
她曾说过：

"It's kind of like a root canal: you waited till the end,
"有点像牙根管治疗：你总是拖到最后才做 \N 但有些事可以预先做好

[but] there are things you could have done beforehand.
"有点像牙根管治疗：你总是拖到最后才做 \N 但有些事可以预先做好

It's like preventative healthcare,
有点像预防性体检, 只不过是预防软件出错"

but it's preventative software."
有点像预防性体检, 只不过是预防软件出错"

As I mentioned in episode 12,
第 12 集提过

breaking big programs into smaller functions allows many people to work simultaneously.
把大项目分解成小函数  可以让多人同时工作

They don't have to worry about the whole thing,
不用关心整个项目，关心自己的函数就好了

just the function they're working on.
不用关心整个项目，关心自己的函数就好了

So, if you're tasked with writing a sort algorithm,
如果你的任务是写排序算法

you only need to make sure it sorts properly and efficiently.
你只需要确保高效和正确就可以了

However, even packing code up into functions isn't enough.
然而把代码打包成函数 依然不够

Microsoft Office probably contains hundreds of thousands of them.
如果只是这样，微软 Office 会有几十万个函数

That's better than dealing with 40 million lines of code,
虽然比 4000 万行代码要好一些，但还是太多了

but it's still way too many "things" for one person or team to manage.
虽然比 4000 万行代码要好一些，但还是太多了

The solution is to package functions into hierarchies,
解决办法是：把函数打包成层级. \N 把相关代码都放在一起，打包成对象（objects）

pulling related code together into "objects".
解决办法是：把函数打包成层级. \N 把相关代码都放在一起，打包成对象（objects）

For example, car's software might have several functions related to cruise control,
例如，汽车软件中 可能有几个和定速巡航有关的函数

like setting speed, nudging speed up or down, and stopping cruise control altogether.
比如 设定速度，逐渐加速减速，停止定速巡航

Since they're all related,
因为这些函数都相关，可以包装成一个"定速巡航对象"

we can wrap them up into a unified cruise control object.
因为这些函数都相关，可以包装成一个"定速巡航对象"

But, we don't have to stop there,
但不止如此，我们还可以做更多

cruise control is just one part of the engine's software.
"定速巡航"只是引擎软件的一部分

There might also be sets of functions that control spark plug ignition,
可能还有 "火花塞点火" "燃油泵" 和 "散热器"

fuel pumps, and the radiator.
可能还有 "火花塞点火" "燃油泵" 和 "散热器"

So we can create a "parent" Engine Object
我们可以做一个"引擎对象" 来包括所有"子"对象

that contains all of these "children" objects.
我们可以做一个"引擎对象" 来包括所有"子"对象

In addition to children *objects*,
除了子对象，"引擎对象"可能有自己的函数

the engine itself might have its *own* functions.
除了子对象，"引擎对象"可能有自己的函数

You want to be able to stop and start it, for example.
比如 开关引擎

It'll also have its own variables,
它也会有自己的变量，比如汽车行驶了多少英里

like how many miles the car has traveled.
它也会有自己的变量，比如汽车行驶了多少英里

In general, objects can contain other objects, functions and variables.
总的来说，对象可以包其它对象，函数和变量

And of course, the engine is just one part of a Car Object.
当然，"引擎对象"只是"汽车对象"的一部分

There's also the transmission, wheels, doors, windows, and so on.
还有传动装置，车轮，门，窗等

Now, as a programmer, if I want to set the cruise control,
作为程序员，如果想设"定速巡航"

I navigate down the object hierarchy,
要一层层向下

from the outermost objects to more and more deeply nested ones.
从最外面的对象往里找

Eventually, I reach the function I want to trigger:
最后找到想执行的函数：

"Car, then engine, then cruise control, then set cruise speed to 55".
Car. Engine.  CruiseControl.  setCruiseSpeed(55)

Programming languages often use something equivalent to the syntax shown here.
编程语言经常用类似这样的语法

The idea of packing up functional units into nested objects is called
把函数打包成对象的思想叫 "面向对象编程"

Object Oriented Programming.
把函数打包成对象的思想叫 "面向对象编程"

This is very similar to what we've done all series long:
这种思想和之前类似

hide complexity by encapsulating low-level details in higher-order components.
通过封装组件，隐藏复杂度

Before we packed up things like transistor circuits into higher-level boolean gates.
之前把晶体管  打包成了逻辑门

Now we're doing the same thing with software.
现在软件也这样做

Yet again, it's a way to move up a new level of abstraction!
又提升了一层抽象！

Breaking up a big program, like a car's software,
把大型软件（如汽车软件）\N 拆成一个个更小单元，适合团队合作

into functional units is perfect for teams.
把大型软件（如汽车软件）\N 拆成一个个更小单元，适合团队合作

One team might be responsible for the cruise control system,
一个团队负责定速巡航系统

and a single programmer on that team tackles a handful of functions.
团队里的一位程序员负责其中一些函数

This is similar to how big, physical things are built, like skyscrapers.
类似建摩天大楼

You'll have electricians running wires,
有电工装电线

plumbers fitting pipes,
管道工配管

welders welding,
焊接工焊接

painters painting,
油漆工涂油漆

and hundreds of other people teeming all over the hull.
还有成百上千人做其他事情

They work together on different parts simultaneously,
在不同岗位同时工作，各尽其能

leveraging their different skills.
在不同岗位同时工作，各尽其能

Until one day, you've got a whole working building!
直到整栋楼完成

But, returning to our cruise control example
回到定速巡航的例子

its code is going to have to make use of functions in other parts of the engine's software,
定速巡航 要用到引擎的其它函数，来保持车速

to, you know, keep the car at a constant speed.
定速巡航 要用到引擎的其它函数，来保持车速

That code isn't part of the cruise control team's responsibility.
定速巡航 团队不负责这些代码，另一个团队负责

It's another team's code.
定速巡航 团队不负责这些代码，另一个团队负责

Because the cruise control team didn't write that,
因为是其他团队的代码，

they're going to need good documentation about what each function in the code does,
定速巡航 团队需要文档 帮助理解代码都做什么

and a well-defined Application Programming Interface
以及定义好的 "程序编程接口" -简称 API

-- or API for short.
以及定义好的 "程序编程接口" -简称 API

You can think of an API as the way that
API 帮助不同程序员合作 \N 不用知道具体细节，只要知道怎么使用就行了

collaborating programmers interact across various parts of the code.
API 帮助不同程序员合作 \N 不用知道具体细节，只要知道怎么使用就行了

For example, in the IgnitionControl object,
例如"点火控制"对象中，可能有"设置发动机转数"函数

there might be functions to set the RPM of the engine,
例如"点火控制"对象中，可能有"设置发动机转数"函数

check the spark plug voltage,
"检查火花塞电压"函数

as well as fire the individual spark plugs.
"点燃单个火花塞"函数

Being able to set the motor's RPM is really useful,
"设置发动机转速"非常有用

the cruise control team is going to need to call that function.
"定速巡航"团队要用到这个函数

But, they don't know much about how the ignition system works.
但他们对点火系统不怎么了解

It's not a good idea to let them call functions that fire the individual spark plugs.
让他们调用"点燃单个火花塞"函数，不是好主意

Or the engine might explode!
引擎可能会炸！

Maybe.
可能啦

The API allows the right people access to the right functions and data.
API 控制哪些函数和数据让外部访问 \N 哪些仅供内部

Object Oriented Programming languages do this
"面向对象"的编程语言 \N 可以指定函数是 public 或 private，来设置权限

by letting you specify whether functions are public or private.
"面向对象"的编程语言 \N 可以指定函数是 public 或 private，来设置权限

If a function is marked as "private",
如果函数标记成 private

it means only functions inside that object can call it.
意味着 只有同一个对象内的其他函数能调用它

So, in this example, only other functions inside of IgnitionControl,
在这个例子里，只有内部函数比如 setRPM

like the setRPM function,
在这个例子里，只有内部函数比如 setRPM

can fire the sparkplugs.
才能调用 fireSparkplug 函数

On the other hand, because the setRPM function is marked as public,
而 setRPM 函数是 public  \N 所以其它对象可以调用它，比如 定速巡航

other objects can call it, like cruise control.
而 setRPM 函数是 public  \N 所以其它对象可以调用它，比如 定速巡航

This ability to hide complexity, and selectively reveal it,
"面向对象编程"的核心是 \N 隐藏复杂度，选择性的公布功能

is the essence of Object Oriented Programming,
"面向对象"的核心是 \N 隐藏复杂度，选择性的公布功能

and it's a powerful and popular way to tackle building large and complex programs.
因为做大型项目很有效，所以广受欢迎

Pretty much every piece of software on your computer, or game running on your console,
计算机上几乎所有软件，游戏机里几乎所有游戏

was built using an Object Oriented Programming Language,
都是 "面向对象" 编程语言写的

like C++, C# or Objective-C.
比如 C++, C#, Objective-C 等

Other popular "OO" languages you may have heard of are Python and Java.
其他流行 OO 语言，你可能听过 Python 和 Java

It's important to remember that code, before being compiled, is just text.
有一点很重要：代码在编译前就只是文字而已

As I mentioned earlier,
前面提过，你可以用记事本或任何文字处理器

you could write code in Notepad or any old word processor.
前面提过，你可以用记事本或任何文字处理器

Some people do.
有人确实这样做

But generally, today's software developers use special-purpose applications for writing programs,
但一般来说，现代软件开发者  会用专门的工具来写代码

ones that integrate many useful tools for writing, organizing, compiling and testing code.
工具里集成了很多有用功能\N 帮助写代码，整理，编译和测代码

Because they put everything you need in one place,
因为集成了所有东西

they're called Integrated Development Environments ,
因此叫 集成开发环境，简称 IDE

or IDEs for short.
因此叫 集成开发环境，简称 IDE

All IDEs provide a text editor for writing code,
所有 IDE 都有写代码的界面

often with useful features like automatic color-coding to improve readability.
还带一些有用功能，比如代码高亮，来提高可读性

Many even check for syntax errors as you type, like spell check for code.
许多 IDE 提供实时检查，比如拼写

Big programs contain lots of individual source files,
大型项目有很多源代码文件

so IDEs allow programmers to organize and efficiently navigate everything.
IDE 帮助开发者整理和看代码

Also built right into the IDE is the ability to compile and run code.
很多 IDE 还可以直接编译和运行代码

And if your program crashes,
如果程序崩了，因为你还没写完呢

because it's still a work in progress,
如果程序崩了，因为你还没写完呢

the IDE can take you back to the line of code where it happened,
IDE 可以定位到出错代码

and often provide additional information to help you track down and fix the bug,
还会提供信息 帮你解决问题

which is a process called debugging.
这叫 调试（debug）

This is important
调试很重要

because most programmers spend 70 to 80% of their time testing and debugging,
大多数程序员会花 70％~80％ 时间调试，而不是在写代码

not writing new code.
大多数程序员会花 70％~80％ 时间调试，而不是在写代码

Good tools, contained in IDEs,
好工具能极大帮助程序员防止和解决错误

can go a long way when it comes to helping programmers prevent and find errors.
好工具能极大帮助程序员防止和解决错误

Many computer programmers can be pretty loyal to their IDEs though
很多开发者只用一款 IDE

But let's be honest.
但承认吧，VIM 才是最棒的编辑器

VIM is where it's at.
但承认吧，VIM 才是最棒的编辑器

Providing you know how to quit.
如果你知道怎么退出的话

In addition to coding and debugging,
除了写代码和调试

another important part of a programmer's job is documenting their code.
程序员工作的另一个重要部分是  给代码写文档

This can be done in standalone files called "readme",
文档一般放在一个叫 README 的文件里

which tell other programmers to read that help file before diving in.
告诉其他程序员，看代码前先看这个文件

It can also happen right in the code itself with comment
文档也可以直接写成"注释"，放在源代码里

These are specially-marked statements that the program knows
注释是标记过的一段文字

to ignore when the code is compiled.
编译代码时  注释会被忽略

They exist only to help programmers figure out what's what in the source code.
注释存在的唯一作用 \N 就是帮助开发者理解代码

Good documentation helps programmers when they revisit code they haven't seen for awhile,
好文档能帮助开发者 \N 几个月后理解自己的代码，对其他人也很重要

but it's also crucial for programmers who are totally new to it.
好文档能帮助开发者 \N 几个月后理解自己的代码，对其他人也很重要

I just want to take a second here and reiterate that it's THE WORST
我想花一秒 再强调一下注释很重要

when someone parachutes a load of uncommented and undocumented code into your lap,
最糟糕的就是拿到一堆代码，没有任何注释和文档

and you literally have to go line by line to understand what the code is doing.
结果得逐行读代码，理解到底干嘛的

Seriously.
我是认真的

Don't be that person.
别做那种人

Documentation also promotes code reuse.
文档还可以提高复用性

So, instead of having programmers constantly write the same things over and over,
与其让程序员一遍遍写同样的东西

they can track down someone else's code that does what they need.
可以直接用别人写好的来解决问题

Then, thanks to documentation,
读文档看怎么用就行，不用读代码

they can put it to work in their program, without ever having to read through the code.
读文档看怎么用就行，不用读代码

"Read the docs" as they say.
"读文档啊"

In addition to IDEs,
除了 IDE，还有一个重要软件帮助团队协作

another important piece of software that
除了 IDE，还有一个重要软件帮助团队协作

helps big teams work collaboratively on big coding projects is called
除了 IDE，还有一个重要软件帮助团队协作

Source Control,
源代码管理

also known as version control or revision control.
也叫"版本控制"

Most often, at a big software company like Apple or Microsoft,
苹果或微软这样的大型软件公司

code for projects is stored on centralized servers,
会把代码放到一个中心服务器上

called a code repository .
叫"代码仓库"

When a programmer wants to work on a piece of code,
程序员想改一段代码时

they can check it out,
可以 check out

sort of like checking out a book out from a library.
有点像从图书馆借书

Often, this can be done right in an IDE.
一般这种操作，可以直接在 IDE 内完成

Then, they can edit this code all they want on their personal computer,
然后开发者在自己的电脑上编辑代码

adding new features and testing if they work.
加新功能，测试

When the programmer is confident their changes are working and there are no loose ends,
如果代码没问题了，所有测试通过了

they can check the code back into the repository,
可以把代码放回去

known as committing code, for everyone else to use.
这叫  提交 (commit)

While a piece of code is checked out,
当代码被 check out，而且可能被改过了

and presumably getting updated or modified,
当代码被 check out，而且可能被改过了

other programmers leave it alone.
其他开发者不会动这段代码

This prevents weird conflicts and duplicated work.
防止代码冲突和重复劳动

In this way, hundreds of programmers can be simultaneously checking in and out pieces of code,
这样多名程序员可以同时写代码，建立庞大的系统

iteratively building up huge systems.
这样多名程序员可以同时写代码，建立庞大的系统

Critically, you don't want someone committing buggy code,
重要的是，你不希望提交的代码里有问题 \N 因为其他人可能用到了这些代码

because other people and teams may rely on it.
重要的是，你不希望提交的代码里有问题 \N 因为其他人可能用到了这些代码

Their code could crash, creating confusion and lost time.
导致他们的代码崩溃，造成困惑而且浪费时间

The master version of the code, stored on the server,
代码的主版本 (master)

should always compile without errors and run with minimal bugs.
应该总是编译正常，尽可能少 bug

But sometimes bugs creep in.
但有时 bug 还是会出现

Fortunately, source control software keeps track of all changes,
幸运的是，源代码管理可以跟踪所有变化

and if a bug is found,
如果发现 bug

the whole code, or just a piece,
全部或部分代码，可以"回滚"到之前的稳定版

can be rolled back to an earlier, stable version.
全部或部分代码，可以"回滚"到之前的稳定版

It also keeps track of who made each change,
"源代码管理" 也记录了谁改了什么代码

so coworkers can send nasty,
所以同事可以给你发 讨厌的

I mean, helpful
我是说"有帮助的" 邮件给写代码的人

and encouraging emails to the offending person.
我是说"有帮助的" 邮件给写代码的人

Debugging goes hand in hand with writing code,
写代码和测代码密不可分

and it's most often done by an individual or small team.
测试一般由个人或小团队完成

The big picture version of debugging is Quality Assurance testing, or QA.
测试可以统称 "质量保证测试"，简称 QA

This is where a team rigorously tests out a piece of software,
严格测试软件的方方面面

attempting to create unforeseen conditions that might trip it up.
模拟各种可能情况，看软件会不会出错

Basically, they elicit bugs.
基本上就是找 bug

Getting all the wrinkles out is a huge effort,
解决大大小小的错误需要很多工作

but vital in making sure the software works
但对确保软件质量至关重要

as intended for as many users in as many situations as imaginable before it ships.
让软件在各种情况下按预期运行

You've probably heard of beta software.
你可能听过 "beta 版" 软件

This is a version of software that's mostly complete,
意思是软件接近完成

but not 100% fully tested.
但不是 100％ 完全测试过

Companies will sometimes release beta versions to the public to help them identify issues,
公司有时会向公众发布 beta 版，以帮助发现问题

it's essentially like getting a free QA team.
用户就像免费的 QA 团队

What you don't hear about as much
你听过比较少的是 \N beta 版之前的版本：alpha 版本

is the version that comes before the beta: the alpha version.
你听过比较少的是 \N beta 版之前的版本：alpha 版本

This is usually so rough and buggy, it's only tested internally.
alpha 版一般很粗糙，错误很多，\N 经常只在公司内部测试

So, that's the tip of the iceberg in terms of the tools, tricks and techniques
以上只是软件工程师用的工具和技巧的冰山一角

that allow software engineers to construct the huge pieces of software that we know and love today,
它们帮助软件工程师制作令人喜爱的软件

like YouTube, Grand Theft Auto 5, and Powerpoint.
如 YouTube，GTA5 和 PPT 等等

As you might expect,
如你所料

all those millions of lines of code needs some serious processing power to run at useful speeds,
这些代码要强大的处理能力 才能高速速度运行

so next episode we'll be talking about how computers got so incredibly fast.
所以下集讨论，计算机怎么发展到如今这么快

See you then.
到时见