编译原理词法分析实验报告

1、实验一 词法分析一、实验目的通过设计编制调试一个具体的词法分析程序，加深对词法分析原理的理解。并掌握在对程序设计语言源程序进行扫描过程中将其分解为各类单词的词法分析方法。编制一个读单词过程，从输入的源程序中，识别出各个具有独立意义的单词，即基本保留字、标识符、常数、运算符、分隔符五大类。并依次输出各个单词的内部编码及单词符号自身值。二、实验内容（1）功能描述：该程序是实现一个词法分析器，词法分析器的功能是输入源程序，输出单词符号。词法分析器的单词符号常常表示成以下的二元式(单词种别码，单词符号的属性值)。本实验中，采用的是将单词分为五种的方法。识别关键字：main、if、int、for、whi

2、le、do、return、break、continue；单词种别码为1。标识符：单词种别码为2。常数：为无符号整形数；单词种别码为3。运算符：包括：+、-、*、/、=、=、=0)a-;Return b;#运行结果：= 测试数据：int a=10,b=5;if(a=9)return b;#运行结果：四、主要源代码/判断是否为字母public boolean IsLetter(char ch) return java.lang.Character.isLetter(ch);/判断是否为数字public boolean IsDigit(char ch) return java.lang.Charac

3、ter.isDigit(ch);public int Reserve() name = new String(allstr).substring(j, index);/ 取子串for (int i = 0; i 5; i+)if (tablei.key.contains(name)return tablei.code;return 0;public static void main(String args) WordAnalyzer a = new WordAnalyzer();ch = a.Getchar();int m = 0;while (ch != #) allstrindex = c

4、h;index+;ch = a.Getchar();int k = index;index = 0;while (j k) m = j;/标示符if (a.IsLetter(allstrj) while (a.IsLetter(allstrindex) | a.IsDigit(allstrindex) index+;if (a.Reserve() != 0)System.out.println( + a.Reserve()+,+name+);elseSystem.out.println(2, +name+ );j = index;/数字if (a.IsDigit(allstrj) while

5、(a.IsDigit(allstrindex)index+;if (a.Reserve() != 0)System.out.println( + a.Reserve()+,+name+);elseSystem.out.println(3, +name+ );j= index;/识别分界符/判断(if (allstrj = () index+;System.out.println( + a.Reserve()+,+name+);j = index;。/识别运算符 /判断=和=if (allstrj = =) index+;if(allstrindex=)index+;System.out.pri

6、ntln(+a.Reserve()+,+name+);j=index;elseSystem.out.println(+a.Reserve()+,+name+);j=index;。5、 实验总结做本次实验大约用了三个小时，用了一个多小时思考，设计，查资料，剩余的时间来编码。由于刚开始对问题的理解不太深入，造成在编码过程中出现了很多问题，一直在考虑是用一个单词一个编码还是将单词分为五种编码，浪费了很长时间，最后选择了将单词分为五种编码的方法来编写词法分析，因为一个编码对应多个单词，考虑到用键值对的形式来存放编码列表。多个固定的单词用ArrayList集合来存储，这些编码数据是固定的，所以定义为st

7、atic类型，只需要初始化一次。在试验中最困难的就是分离出关键字、标识符、数字、运算符和分界符，通过调试观察变量的值，修改，调试，运行。来回重复，最后的得到了正确的运行结果。package com.fgy.practice;import java.util.ArrayList;import java.util.List;public class WordAnalyzer static char ch;static int index = 0;static int j = 0;static char allstr = new char;static String name;static KeyT

8、able table=new KeyTable5;staticList al=new ArrayList();al.add(main);al.add(if);al.add(else);al.add(int);al.add(for);al.add(while);al.add(return);List al1=new ArrayList();List al2=new ArrayList();List al3=new ArrayList();al3.add(+);al3.add(+);al3.add(-);al3.add(-);al3.add(=);al3.add(=);al3.add();al3.

9、add(=);al3.add();al3.add(=);List al4=new ArrayList();al4.add(,);al4.add(;);al4.add();al4.add();al4.add();al4.add();table0=new KeyTable(al,1);/关键字table1=new KeyTable(al1,2);/标示符table2=new KeyTable(al2,3);/常数table3=new KeyTable(al3,4);/运算符table4=new KeyTable(al4,5);/分界符/从键盘获取一个一个的字符public char Getchar

10、() try ch = (char) System.in.read(); catch (Exception e) e.printStackTrace();return ch;/判断是否为字母public boolean IsLetter(char ch) return java.lang.Character.isLetter(ch);/判断是否为数字public boolean IsDigit(char ch) return java.lang.Character.isDigit(ch);public int Reserve() name = new String(allstr).substr

11、ing(j, index);/ 取子串for (int i = 0; i 5; i+)if (tablei.key.contains(name)return tablei.code;return 0;public static void main(String args) WordAnalyzer a = new WordAnalyzer();ch = a.Getchar();int m = 0;while (ch != #) allstrindex = ch;index+;ch = a.Getchar();int k = index;index = 0;while (j k) m = j;/

12、标示符if (a.IsLetter(allstrj) while (a.IsLetter(allstrindex) | a.IsDigit(allstrindex) index+;if (a.Reserve() != 0)System.out.println( + a.Reserve()+,+name+);elseSystem.out.println(2, +name+ );j = index;/数字if (a.IsDigit(allstrj) while (a.IsDigit(allstrindex)index+;if (a.Reserve() != 0)System.out.println

13、( + a.Reserve()+,+name+);elseSystem.out.println(3, +name+ );j= index;/识别分界符/判断(if (allstrj = () index+;System.out.println( + a.Reserve()+,+name+);j = index;/判断)if (allstrj = ) index+;System.out.println( + a.Reserve()+,+name+);j = index;/判断if (allstrj = ) index+;System.out.println( + a.Reserve()+,+na

14、me+);j = index;/判断if (allstrj = ) index+;System.out.println( + a.Reserve()+,+name+);j = index;/判断 ；if (allstrj = ;) index+;System.out.println( + a.Reserve()+,+name+);j = index;/判断，if (allstrj = ,) index+;System.out.println( + a.Reserve()+,+name+);j = index;/识别运算符 /判断=和=if (allstrj = =) index+;if(all

15、strindex=)index+;System.out.println(+a.Reserve()+,+name+);j=index;elseSystem.out.println(+a.Reserve()+,+name+);j=index;/判断和=if (allstrj = 和=if (allstrj = ) index+;if (allstrindex = =) index+;System.out.println( +a.Reserve()+,+name+);j = index; elseSystem.out.println( +a.Reserve()+,+name+);j = index;

16、/判断+和+if (allstrj = +) index+;if (allstrindex = +) index+;System.out.println( +a.Reserve()+,+name+);j = index; elseSystem.out.println( +a.Reserve()+,+name+);j = index;/判断-和-if (allstrj = -) index+;if (allstrindex = -) index+;System.out.println( +a.Reserve()+,+name+);j = index; elseSystem.out.println( +a.Reserve()+,+name+);j