目录

• I. Intro —— 写java的初体验，解了problem set 0
• II. Testing —— 不同test的区别
• III. Specification —— 不同spec的区别，以及如何写好
• IIII. Snapshot Diagram —— 不同符号的含义

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I. Intro

1. Coding Descipline

• Safe from bugs
• Easy to understand
• Ready for change

2. Java语法memo

• 继承

以官网doc的例子。Mountain / Road / Tandem Bike三种，都是Bicycle，但是增加了不同的feature。因而，OOP中，允许继承。此时，Bicycle是其他三者的superclass；Mountain / Road / Tandem Bike则是subclasses。

Bicyle的继承
Syntax用了```extends``，继承写起来，大概长这样👇：

public class MountainBike extends Bicycle {
        
    // the MountainBike subclass has
    // one field
    public int seatHeight;

    // the MountainBike subclass has
    // one constructor
    public MountainBike(int startHeight, int startCadence,
                        int startSpeed, int startGear) {
        super(startCadence, startSpeed, startGear);
        seatHeight = startHeight;
    }   
        
    // the MountainBike subclass has
    // one method
    public void setHeight(int newValue) {
        seatHeight = newValue;
    }   

}

• if语句: "?"

if ( a > b ) {
    max = a;
} else {
    max = b
}

简写成

max = (a > b) ? a: b;

3. Problem set 0心得

1. 做problem set 0的时候，放弃了最后三题，看不懂atan的数学问题。希望后面的problem set不要出现一样的...🤦‍♂️。
2. 有一个之前完全没有注意的，就是magic number。忽然就声明了一个数字，其实违反了easy to understand。合适的方法是，声明一个变量，然后comment它的含义。有时候需要final它。
3. unit test的重要性，下assert，做好每个unit的debug。
4. float和double区别在于32bit和64bit，所以用 double更安全。
5. 前面那个javadoc，也从没写过，好像挺方便的。写javadoc，有一个关键的准则，是：NEVER talk about local variables of the method or private fields.
   NEVER talk about local variables of the method or private fields.

模板大概是：

/**
brief description, what is this method for?
@param parameterName What is the parameter for?
@return value What is the value meaning?
**/

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II. Testing

1. Residual defect rates

• 1 - 10 defects/kloc: Typical industry software.
• 0.1 - 1 defects/kloc: High-quality validation. The Java libraries might achieve this level of correctness.
• 0.01 - 0.1 defects/kloc: The very best, safety-critical validation. NASA and aerospace companies can achieve this level.

kloc : 1000 lines of source code.

2. Testing

• Test-first programming. Write tests before you write code.
• Partitioning and boundaries for choosing test cases systematically.
• White box testing and statement coverage for filling out a test suite.
• Unit-testing each module in isolation as much as possible.
• Automated regression testing to keep bugs from coming back.

2.1 Unit Tests

Testing modules in isolation leads to much easier debugging.

2.2 Regression Testing

Regression意味着，在改bug-A或者增加feature-B的时候，又多了新的bug-B。在test-first debugging中，把之前的bug-A的test case增加到test suite中，这样写完B后，可以确定A不会再发生。

3. 心得

之前对unit test没啥概念，意味只要分模块写code就好。但是，每个模块的debugging和test case，要考虑到模块中，也就是test-first programming的重要性。Write tests before you write code.

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III. Specification

1. underdetermined specs & nondeterminism 定义

• deterministic spec: 1 input → 1 output
• under-deterministic spec: 1 input → >1 outputs
• under-deterministic spec can have determined implementation

2. declarative vs. operational specs 定义

• operational specs → spec中写了method运行的步骤
• declarative specs (better) → spec不提供内部的步骤，只提供outcome的properties

3. 好的specs长什么样？

• better spec👍 → weaker precondition🔽 & stronger postcondition🔼

4. 如何写好spec？

• brief & clear & structured
• coherent inputs
• no global variables & no printing (instead of returning)
• no making internal helper methods public （helper method only for local use）

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IIII. Snapshot Diagram

1. → variable
2. ⇒ final
3. → ⚪
4. → ⭕(double circles)

5. List

   
   Lists

6. Set

   
   Set

7. Map

   
   Map

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6.005.1x，自学的第一个礼拜。💻🔨
整个版面乱成一锅粥。或许应该再开一个post，来整理知识点吧。🤦‍♂️

Ronn Liu 🙋‍♂️
2019/01/01 - 2019/01/06 📌