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首先看下我们要分析的代码段如下：
输出结果如下：
输出结果(a).png
输出结果(b).png
输出结果(c).png
括号里是一个二元式：（单词类别编码，单词位置编号）
代码如下：
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package yue.lexicalanalyzer;
import java.io.*;
/*
* 主程序
*/
public class main {
public static void main(string[] args) throws ioexception {
lexer lexer = new lexer();
lexer.printtoken();
lexer.printsymbolstable();
}
}
package yue.lexicalanalyzer;
import java.io.*;
import java.util.*;
/*
* 词法分析并输出
*/
public class lexer {
/*记录行号*/
public static int line = 1;
/*存放最新读入的字符*/
char character = ' ';
/*保留字*/
hashtable<string, keyword> keywords = new hashtable<string, keyword>();
/*token序列*/
private arraylist<token> tokens = new arraylist<token>();
/*符号表*/
private arraylist<symbol> symtable = new arraylist<symbol>();
/*读取文件变量*/
bufferedreader reader = null;
/*保存当前是否读取到了文件的结尾*/
private boolean isend = false;
/* 是否读取到文件的结尾 */
public boolean getreaderstate() {
return this.isend;
}
/*打印tokens序列*/
public void printtoken() throws ioexception {
filewriter writer = new filewriter("e:\\lex.txt");
system.out.println("词法分析结果如下：");
system.out.print("杜悦-2015220201031\r\n\n");
writer.write("杜悦-2015220201031\r\n\r\n");
while (getreaderstate() == false) {
token tok = scan();
string str = "line " + tok.line + "\t(" + tok.tag + "," + tok.pos + ")\t\t"
+ tok.name + ": " + tok.tostring() + "\r\n";
writer.write(str);
system.out.print(str);
}
writer.flush();
}
/*打印符号表*/
public void printsymbolstable() throws ioexception {
filewriter writer = new filewriter("e:\\symtab1.txt");
system.out.print("\r\n\r\n符号表\r\n");
system.out.print("编号\t行号\t名称\r\n");
writer.write("符号表\r\n");
writer.write("编号 " + "\t行号 " + "\t名称 \r\n");
iterator<symbol> e = symtable.iterator();
while (e.hasnext()) {
symbol symbol = e.next();
string desc = symbol.pos + "\t" + symbol.line + "\t" + symbol.tostring();
system.out.print(desc + "\r\n");
writer.write(desc + "\r\n");
}
writer.flush();
}
/*打印错误*/
public void printerror(token tok) throws ioexception{
filewriter writer = new filewriter("e:\\error.txt");
system.out.print("\r\n\r\n错误词法如下：\r\n");
writer.write("错误词法如下：\r\n");
string str = "line " + tok.line + "\t(" + tok.tag + "," + tok.pos + ")\t\t"
+ tok.name + ": " + tok.tostring() + "\r\n";
writer.write(str);
}
/*添加保留字*/
void reserve(keyword w) {
keywords.put(w.lexme, w);
}
public lexer() {
/*初始化读取文件变量*/
try {
reader = new bufferedreader(new filereader("e:\\输入.txt"));
} catch (ioexception e) {
system.out.print(e);
}
/*添加保留字*/
this.reserve(keyword.begin);
this.reserve(keyword.end);
this.reserve(keyword.integer);
this.reserve(keyword.function);
this.reserve(keyword.read);
this.reserve(keyword.write);
this.reserve(keyword.aif);
this.reserve(keyword.athen);
this.reserve(keyword.aelse);
}
/*按字符读*/
public void readch() throws ioexception {
character = (char) reader.read();
if ((int) character == 0xffff) {
this.isend = true;
}
}
/*判断是否匹配*/
public boolean readch(char ch) throws ioexception {
readch();
if (this.character != ch) {
return false;
}
this.character = ' ';
return true;
}
/*数字的识别*/
public boolean isdigit() throws ioexception {
if (character.isdigit(character)) {
int value = 0;
while (character.isdigit(character)) {
value = 10 * value + character.digit(character, 10);
readch();
}
num n = new num(value);
n.line = line;
tokens.add(n);
return true;
} else
return false;
}
/*保留字、标识符的识别*/
public boolean isletter() throws ioexception {
if (character.isletter(character)) {
stringbuffer sb = new stringbuffer();
/*首先得到整个的一个分割*/
while (character.isletterordigit(character)) {
sb.append(character);
readch();
}
/*判断是保留字还是标识符*/
string s = sb.tostring();
keyword w = keywords.get(s);
/*如果是保留字的话，w不应该是空的*/
if (w != null) {
w.line = line;
tokens.add(w);
} else {
/*否则就是标识符，此处多出记录标识符编号的语句*/
symbol sy = new symbol(s);
symbol mark = sy; //用于标记已存在标识符
boolean isrepeat = false;
sy.line = line;
for (symbol i : symtable) {
if (sy.tostring().equals(i.tostring())) {
mark = i;
isrepeat = true;
}
}
if (!isrepeat) {
sy.pos = symtable.size() + 1;
symtable.add(sy);
} else if (isrepeat) {
sy.pos = mark.pos;
}
tokens.add(sy);
}
return true;
} else
return false;
}
/*符号的识别*/
public boolean issign() throws ioexception {
switch (character) {
case '#':
readch();
allend.allend.line = line;
tokens.add(allend.allend);
return true;
case '\r':
if (readch('\n')) {
readch();
lineend.lineend.line = line;
tokens.add(lineend.lineend);
line++;
return true;
}
case '(':
readch();
delimiter.lpar.line = line;
tokens.add(delimiter.lpar);
return true;
case ')':
readch();
delimiter.rpar.line = line;
tokens.add(delimiter.rpar);
return true;
case ';':
readch();
delimiter.sem.line = line;
tokens.add(delimiter.sem);
return true;
case '+':
readch();
calcword.add.line = line;
tokens.add(calcword.add);
return true;
case '-':
readch();
calcword.sub.line = line;
tokens.add(calcword.sub);
return true;
case '*':
readch();
calcword.mul.line = line;
tokens.add(calcword.mul);
return true;
case '/':
readch();
calcword.div.line = line;
tokens.add(calcword.div);
return true;
case ':':
if (readch('=')) {
readch();
calcword.assign.line = line;
tokens.add(calcword.assign);
return true;
}
break;
case '>':
if (readch('=')) {
readch();
calcword.ge.line = line;
tokens.add(calcword.ge);
return true;
}
break;
case '<':
if (readch('=')) {
readch();
calcword.le.line = line;
tokens.add(calcword.le);
return true;
}
break;
case '!':
if (readch('=')) {
readch();
calcword.ne.line = line;
tokens.add(calcword.ne);
return true;
}
break;
}
return false;
}
/*下面开始分割关键字，标识符等信息*/
public token scan() throws ioexception {
token tok;
while (character == ' ')
readch();
if (isdigit() || issign() || isletter()) {
tok = tokens.get(tokens.size() - 1);
} else {
tok = new token(character);
printerror(tok);
}
return tok;
}
}
package yue.lexicalanalyzer;
/*
* token父类
*/
public class token {
public final int tag;
public int line = 1;
public string name = "";
public int pos = 0;
public token(int t) {
this.tag = t;
}
public string tostring() {
return "" + (char) tag;
}
}
package yue.lexicalanalyzer;
/*
* 单词类别赋值
*/
public class tag {
public final static int
begin = 1, //保留字
end = 2, //保留字
integer = 3, //保留字
function = 4, //保留字
read = 5, //保留字
write = 6, //保留字
if = 7, //保留字
then = 8, //保留字
else = 9, //保留字
symbol = 11, //标识符
constant = 12, //常数
add = 13, //运算符 "+"
sub = 14, //运算符 "-"
mul = 15, //运算符 "*"
div = 16, //运算符 "/"
le = 18, //运算符 "<="
ge = 19, //运算符 ">="
ne = 20, //运算符 "!="
assign = 23, //运算符 ":="
lpar = 24, //界符 "("
rpar = 25, //界符 ")"
sem = 26, //界符 ";"
line_end = 27, //行尾符
all_end = 28; //结尾符 "#"
}
package yue.lexicalanalyzer;
/**
* 保留字
*/
public class keyword extends token {
public string lexme = "";
public keyword(string s, int t) {
super(t);
this.lexme = s;
this.name = "保留字";
}
public string tostring() {
return this.lexme;
}
public static final keyword
begin = new keyword("begin", tag.begin),
end = new keyword("end", tag.end),
integer = new keyword("integer", tag.integer),
function = new keyword("function", tag.function),
read = new keyword("read", tag.read),
write = new keyword("write", tag.write),
aif = new keyword("if", tag.if),
athen = new keyword("then", tag.then),
aelse = new keyword("else", tag.else);
}
package yue.lexicalanalyzer;
/*
* 标识符
*/
public class symbol extends token {
public string lexme = "";
public symbol(string s) {
super(tag.symbol);
this.lexme = s;
this.name = "标识符";
}
public string tostring() {
return this.lexme;
}
}
package yue.lexicalanalyzer;
/**
* 运算符
*/
public class calcword extends token {
public string lexme = "";
public calcword(string s, int t) {
super(t);
this.lexme = s;
this.name = "运算符";
}
public string tostring() {
return this.lexme;
}
public static final calcword
add = new calcword("+", tag.add),
sub = new calcword("-", tag.sub),
mul = new calcword("*", tag.mul),
div = new calcword("/", tag.div),
le = new calcword("<=", tag.le),
ge = new calcword(">=", tag.ge),
ne = new calcword("!=", tag.ne),
assign = new calcword(":=", tag.assign);
}
package yue.lexicalanalyzer;
/**
* 界符
*/
public class delimiter extends token {
public string lexme = "";
public delimiter(string s, int t) {
super(t);
this.lexme = s;
this.name = "界符";
}
public string tostring() {
return this.lexme;
}
public static final delimiter
lpar = new delimiter("(", tag.lpar),
rpar = new delimiter(")", tag.rpar),
sem = new delimiter(";", tag.sem);
}
package yue.lexicalanalyzer;
/*
* 常数
*/
public class num extends token {
public final int value;
public num(int v) {
super(tag.constant);
this.value = v;
this.name = "常数";
}
public string tostring() {
return "" + value;
}
}
package yue.lexicalanalyzer;
/**
* 行尾符
*/
public class lineend extends token {
public string lexme = "";
public lineend(string s) {
super(tag.line_end);
this.lexme = s;
this.name = "行尾符";
}
public string tostring() {
return this.lexme;
}
public static final lineend lineend = new lineend("\r\n");
}
package yue.lexicalanalyzer;
/**
* 结尾符
*/
public class allend extends token {
public string lexme = "";
public allend(string s) {
super(tag.all_end);
this.lexme = s;
this.name = "结尾符";
}
public string tostring() {
return this.lexme;
}
public static final allend allend = new allend("#");
}
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