System Software Software Engineering Department of Computer Science

程序编码 董渊 ( System Software & Software Engineering) Department of Computer Science & Technology Tsinghua University 2005 ~ 2008 Copyright @ Tsinghua University Page 1

程序设计风格 – 基本原则 Top-down flow • Have the required action follow soon after the decision that generates it Generality is a virtue • Trade-off: generality, performance, understanding Dependence among components must be visible 2005 ~ 2008 Copyright @ Tsinghua University Page 4

benefit = minimum; if (age<75) goto A; benefit = maximum; goto C; if (age<65) goto B; if (age<55) goto C; A: if (age<65) goto B; benefit = benefit * 1. 5 + bonus; goto C; B: if (age<55) goto C; benefit = benefit * 1. 5; C: next statement if (age < 55) benefit = minimum; elseif (age < 65) benefit = munimum + bonus; elseif (age < 75) benefit = munimum * 1. 5 + bonus; else benefit = maximum; 2005 ~ 2008 Copyright @ Tsinghua University Page 5

程序设计风格– 基本原则 Do not sacrifice clarity and correctness for speed • • Cost to write faster code Cost to test more complex code Cost to maintain more complex/less understandable code Let compiler and other tools do it Choose data structure to simplify the program’s calculation 2005 ~ 2008 Copyright @ Tsinghua University Page 6

1. 2. 3. 4. 5. For the first $10, 000 of income, the tax is 10%. For the next $10, 000 of income above $10, 000, the tax is 12%. For the next $10, 000 of income above $20, 000, the tax is 15%. For the next $10, 000 of income above $30, 000, the tax is 18%. For any income above $40, 000, the tax is 20%. Tax Table Bracket Base Percent 0 0 10 10, 000 12 20, 000 2200 15 30, 000 3700 18 40, 000 5500 20 2005 ~ 2008 tax = base[level] + percent[level] * (taxable_income – bracket[level]） Copyright @ Tsinghua University Page 7

程序设计风格– 基本原则 Localizing input and output • • Hardware/software dependence Easy to change Including pseudocode • Adapt design to chosen language Revising and rewriting, not patching • Module decomposition, control structure, data structure, algorithm, etc. 2005 ~ 2008 Copyright @ Tsinghua University Page 8

程序设计风格– 基本原则 Documentation : written description of WHAT the programs do and HOW they do it • Self-Documentation, Source code Internal documentation • External documentation • Header comment block • Program comments • Meaningful variable names and statement labels • Formatting to enhance understanding • Documenting data • Problem, algorithm, data 2005 ~ 2008 Copyright @ Tsinghua University Page 9

内容提要 基本目标 程序设计风格 Java程序设计风格 程序复杂性度量 2005 ~ 2008 Copyright @ Tsinghua University Page 10

命名规则 包（Packages），体系结构 接口（Interfaces），联系（内外部） 类（Classes），基本模块 方法（Methods），服务，消息 变量（Variables），属性 常量（Constants），属性 2005 ~ 2008 Copyright @ Tsinghua University Page 12

命名规则 包 • 前缀（顶层） • 小写ASCII字母 • ISO 3166(1981)的Internet域名规范： • • 如com, edu, org, net, gov, mil 如cn, tw, hk, jp, uk • 后继可根据项目结构： • 例如： • 所在组织的组织结构 • 或内部命名规范 • com. sun. security； • org. omg. CORBA • edu. tsinghua. course 11. group 4 • java. awt 2005 ~ 2008 Copyright @ Tsinghua University Page 13

命名规则 接口 • 名词或形容词组合中，每个词的首字母大写 • 尽量简单明确 • 尽量用全名，或用极为通用的缩写如URL，HTML • 例如： • Serializable；Adjustable； • Runnable；Cloneable • Action. Listener； • Mouse. Listener • Iterator；Enumeration 2005 ~ 2008 Copyright @ Tsinghua University Page 14

命名规则 常量 • 大写字母 • 单词之间用“_”连接 • 例如： • Color. BLACK，Color. GREEN； • JOption. Pane. ERROR_MESSAGE， JOption. Pane. YES_NO_CANCEL_OPTION； 2005 ~ 2008 Copyright @ Tsinghua University Page 18

/* * 文件名 * * 版本信息 * * ��（开���、修改的�史��） * * Copyright notice */ package homework; import java. util. Vector; import java. awt. *; 2005 ~ 2008 Copyright @ Tsinghua University Page 20

/** * �的主要功能描述 * * @version 版本名称及开��� * @author 作者名 * @modified by: * 更改的�史��，包括作者、�� */ public class Blah extends Some. Class { /* A class implementation comment can go here. */ 2005 ~ 2008 Copyright @ Tsinghua University Page 21

/** class. Var 1 documentation comment */ public static int class. Var 1; /** * class. Var 2 documentation comment that happens to * be more than one line long */ private static Object class. Var 2; /** instance. Var 1 documentation comment */ public Object instance. Var 1; /** instance. Var 2 documentation comment */ protected int instance. Var 2; /** instance. Var 3 documentation comment */ private Object[] instance. Var 3; 2005 ~ 2008 Copyright @ Tsinghua University Page 22

/** *. . . constructor Blah documentation comment. . . */ public Blah() { //. . . implementation goes here. . . } 2005 ~ 2008 Copyright @ Tsinghua University Page 23

/** *. . . method do. Something documentation comment. . . */ public void do. Something() { //. . . implementation goes here. . . } /** *. . . method do. Something. Else documentation comment. . * @param some. Param description */ public void do. Something. Else(Object some. Param) { //. . . implementation goes here. . . } } 2005 ~ 2008 Copyright @ Tsinghua University Page 24

some. Method(long. Expression 1, long. Expression 2, long. Expression 3, long. Expression 4, long. Expression 5); var = some. Method 1(long. Expression 1, some. Method 2(long. Expression 2, long. Expression 3)); long. Nm 1 = long. Nm 2 * (long. Nm 3 + long. Nm 4 - long. Nm 5) + 4 * long. Nm 6; // PREFER long. Nm 1 = long. Nm 2 * (long. Nm 3 + long. Nm 4 - long. Nm 5) + 4 * long. Nm 6; // AVOID 2005 ~ 2008 Copyright @ Tsinghua University Page 26

/* * Here is a block comment. */ if (condition) { /* Handle the condition. */. . . } if (a == 2) { return TRUE; /* special case */ } else { return is. Prime(a); /* works only for odd a */ } 2005 ~ 2008 Copyright @ Tsinghua University Page 28

if (foo > 1) { // Do a double-flip. . } else { return false; // Explain why here. } //if (bar > 1) { // // // Do a triple-flip. //. . . //} //else { // return false; //} 2005 ~ 2008 Copyright @ Tsinghua University Page 29

程序注释 Documentation Comments • • Javadoc /**………*/ @return @param @see @since @link HTML标识 2005 ~ 2008 Copyright @ Tsinghua University Page 30

/** * Returns an Image object that can then be painted on the screen. * The url argument must specify an absolute {@link URL}. * <p> * This method always returns immediately, whether or not the * image exists. When this applet attempts to draw the image on * the screen, the data will be loaded. The graphics primitives * that draw the image will incrementally paint on the screen. * * @param url an absolute URL giving the base location of the image * @param name the location of the image, relative to the URL argument * @return the image at the specified URL * @see Image */ public Image get. Image(URL url, String name) { …… } 2005 ~ 2008 Copyright @ Tsinghua University Page 31

2005 ~ 2008 Copyright @ Tsinghua University Page 32

程序声明 每个声明一行，以便于添加注释 //preferred int level; // indentation level int size; // size of table //avoid int level，size; 类型和标识符间要有空格（或Tab）分隔 int level; // indentation level int size; // size of table Object current. Entry; // currently selected table entry 2005 ~ 2008 Copyright @ Tsinghua University Page 33

程序声明 初始化：尽量在变量声明的同时赋初值 声明的位置：尽量在程序块的开始部分 void my. Method() { int 1 = 0; // beginning of method block if (condition) { int 2 = 0; // beginning of "if" block. . . } } 2005 ~ 2008 Copyright @ Tsinghua University Page 34

程序声明 避免局部变量与高层变量重名。 int count; . . . my. Method() { if (condition) { int count = 0; // AVOID!. . . } 2005 ~ 2008 Copyright @ Tsinghua University Page 35

class Sample extends Object { int ivar 1; int ivar 2; Sample(int i, int j) { ivar 1 = i; ivar 2 = j; } int empty. Method() {}. . . } 2005 ~ 2008 Copyright @ Tsinghua University Page 37

语句结构 简单语句 • 每一条语句单独一行 复合语句 • • 用缩进明确语句间的层次关系 if-then-else语句 for while do-while switch try-catch 2005 ~ 2008 Copyright @ Tsinghua University Page 38

if (condition) { statements; } else { statements; } if (condition) { statements; } else{ statements; } 2005 ~ 2008 Copyright @ Tsinghua University Page 39

for (initialization; condition; update) { statements; } for (initialization; condition; update); while (condition) { statements; } while (condition); do { statements; } while (condition); 2005 ~ 2008 Copyright @ Tsinghua University Page 40

switch (condition) { case ABC: statements; /* falls through */ case DEF: statements; break; case XYZ: statements; break; default: statements; break; } 2005 ~ 2008 Copyright @ Tsinghua University Page 41

try { statements; } catch (Exception. Class e) { statements; } finally { statements; } 2005 ~ 2008 Copyright @ Tsinghua University Page 42

内容提要 基本目标 程序设计风格 Java程序设计风格 程序复杂性度量 2005 ~ 2008 Copyright @ Tsinghua University Page 45

A开始 A B B C�入 C D K�出 D E L�束 E F J L G G H H�入 程序� 程序流程� 2005 ~ 2008 K Copyright @ Tsinghua University Page 49

1 2 V=1 -2+2 =0+1 =1 1 2 3 4 顺序型 选择型 1 1 2 3 V=3 -3+2 =1+1 =2 While型循环 2005 ~ 2008 2 3 V=4 -4+2 =1+1 =2 V=3 -3+2 =1+1 =2 Until型循环 Copyright @ Tsinghua University Page 51

1 2 3 4 I 5 II IV 6 7 8 9 V=11 -9+2=3+1=4 2005 ~ 2008 Copyright @ Tsinghua University Page 52