词法分析代码。

import java.io.*;

import java.util.Vector;

import java.util.regex.*;

public class Compiler {

public static String stringCompiler="";

private static final String[] KEY_WORD={"if", "then", "while"," do"," read"," write","call",

"begin", "end", "const", "procedure", "odd"};

private static boolean isKeyWord(String s) //是否是关键字 {

boolean b=false;

for(int i=0;i<KEY_WORD.length;i++)

if(s.equals(KEY_WORD[i]))

b=true;

return b;

}

class Element{

String s;

String kind;

String gets(){return s;}

String getkind(){return kind;}

Element(String s,String kind){

this.s = s;

this.kind = kind;

}

}

static Vector<Element> sheet = new Vector<Element>(8); File result = new File("result.txt");

File result1 = new File("result1.txt");

boolean work(){

System.out.println("输入PL/O语言为：");

try{

FileWriter fw1 = new FileWriter(result1);

BufferedWriter bw1 = new BufferedWriter(fw1); FileReader fr1 = new FileReader("input.txt"); BufferedReader br1 = new BufferedReader(fr1); , "var"

String s = br1.readLine();

label1:

while(s!=null)

{

for(int i = 0;i<s.length();i++){

if(s.indexOf("//")!=-1) //两个'/'符

{

s=s.substring(0, s.indexOf("//")); s=s.replaceAll("\t", " ");

s=s.replaceAll("\n", " ");

s=s.toLowerCase();

bw1.write(s);

System.out.println(s);

bw1.newLine();

s = br1.readLine();

continue label1;

}

else if(s.indexOf("/*")!=-1) // '/'符和'*'符

{

s=s.substring(0, s.indexOf("/*"));

s.replaceAll("\t", " ");

s.replaceAll("\n", " ");

s.toLowerCase();

bw1.write(s.substring(0, i));

System.out.println(s);

s=s.substring(i,s.length());

while(s!=null){

if(s.indexOf("*/")!=-1)

{

s=s.substring(s.lastIndexOf("*/"),s.length()); s=s.replaceAll("\t", " ");

s=s.replaceAll("\n", " ");

s=s.toLowerCase();

bw1.write(s);

System.out.println(s);

bw1.newLine();

s = br1.readLine();

continue label1;

}

else

{

s = br1.readLine();

}

}

}

else{

s=s.replaceAll("\t", " ");

s=s.replaceAll("\n", " ");

s=s.toLowerCase();

bw1.write(s);

System.out.println(s);

bw1.newLine();

s = br1.readLine();

continue label1;

}

}

}

br1.close();

bw1.close();

return true;

}catch(IOException e){

e.printStackTrace();

return false;

}

finally{

}

}

void analyser(){

try{

BufferedReader br = new BufferedReader(new FileReader(result1)); BufferedWriter bw = new BufferedWriter(new FileWriter(result));

String a = br.readLine();

while(a!=null){

Matcher m =

Pattern.compile("/\\*.*\\*/|\'.+\'|(\\++|\\--|\\>=|\\<=)|\\d+\\.\\d*|\\w+|\".+\"|\\S").matcher(a);

while (m.find()) {

checkScan(m.group());

}

String s=Compiler.stringCompiler;

System.out.flush();

bw.write(s);

Compiler.stringCompiler="";

a = br.readLine();

}

br.close();

bw.close();

}catch(IOException e)

{e.printStackTrace();}

}

public void checkScan(String s)

{

if(Character.isDigit(s.charAt(0)))

checkDigitCompiler(s);

else if(s.length()==1)

checkCharCompiler(s.charAt(0)); else

checkStringCompiler(s);

}

private void checkDigitCompiler(String s) //检测数字 {

if(s.indexOf(".")!=-1)

{

CompilerOut(Double.valueOf(s).toString()); sheet.add(new Element(s,"小数"));

}

else

{

CompilerOut(s);

sheet.add(new Element(s,"整数"));

}

}

private void checkCharCompiler(char c) //检测单个字符 {

switch (c)

{

case '<':

sheet.add(new Element(new Character(c).toString() ,"小于号

")); //扫描文件

break; case '>': sheet.add(new Element(c+"","大于号")); break; case '=': sheet.add(new Element(c+"","等于号")); break; case '+': sheet.add(new Element(c+"","加号")); break; case '-': sheet.add(new Element(c+"","减号")); break; case '*': sheet.add(new Element(c+"","乘号")); break; case '/': sheet.add(new Element(c+"","除号")); break; case '(': sheet.add(new Element(c+"","左小括号")); break; case ')': sheet.add(new Element(c+"","右小括号")); break; case '[': sheet.add(new Element(c+"","左中括号")); break; case ']': sheet.add(new Element(c+"","右中括号")); break; case '{': sheet.add(new Element(c+"","左大括号")); break; case '}': sheet.add(new Element(c+"","右大括号")); break; case ',': sheet.add(new Element(c+"","逗号")); break; case ';': sheet.add(new Element(c+"","分号")); break; case '!':

sheet.add(new Element(c+"","取反")); break; case '.': sheet.add(new Element(c+"","点号")); break; case ':': sheet.add(new Element(c+"","冒号")); case '?': sheet.add(new Element(c+"","问号")); break; default: sheet.add(new Element(c+"","标识符")); break; }

}

private void checkStringCompiler(String s) //检测多个字符

{

CompilerOut( s);

if(isKeyWord(s))

sheet.add(new Element(s,"关键字"));

else

sheet.add(new Element(s,"标识符"));

}

private void CompilerOut(Object o) //向显示器输出结果预编译结果 {

if(o instanceof String)

{

stringCompiler=stringCompiler+(String)o+" "; }

else

{

stringCompiler=stringCompiler+((Character)o).charValue()+" "; }

}

public static void main(String[] args) throws Exception {

System.out.println("*****************************************************");

Compiler c = new Compiler();

if(c.work())

{

//System.out.println("已将处理后代码放入 result1.txt 中！"); }

else

System.out.println("预处理失败！");

System.out.println("输入 y开始词法分析");

char k = 'y';

while(k!=(char)System.in.read())

System.out.println("请输入y");

c.analyser();

System.out.println(" ");

////System.out.println("\n类型 单词符号"); // System.out.println(" 0 标识符");

// System.out.println(" 1 常数 ");

// System.out.println(" 2 关键字");

for(int i=0;i<sheet.size();i++)

{

Element element = (Element) sheet.elementAt(i);

System.out.println("单词： "+element.s+"\t"+"\t"+"\t"+" 型： "+element.getkind());

}

}

}

运行结果。 *****************************************************

输入PL/O语言为：

if i>0 i=1;

输入 y开始词法分析 y

单词： if 类型： 关键字

单词： i 类型： 标识符

单词： > 类型： 大于号

单词： 0 类型： 整数

单词： i 类型： 标识符

单词： = 类型： 等于号

单词： 1 类型： 整数

单词： ; 类型： 分号 类