使用JAVA实现PL0语言的词法分析器

用直接转向法实现有限自动机的代码

枚举类

import java.util.UUID;/*** @author HJC* @version 1.0* @apiNote PL0语言单词分类* @since 2021/11/6*/
public enum PL0 {IDENTIFIER("IDENTIFIER", 1),INTEGER("INTEGER", 2),ADD("+", 3),SUB("-", 4),MUL("*", 5),DIV("/", 6),EQL("=", 7),GT(">", 8),LT("<", 9),NE("<>", 10),LE("<=", 11),GE(">=", 12),LS("(", 13),RS(")", 14),LB("{", 15),RB("}", 16),SEM(";", 17),DOT(",", 18),YY("\"", 19),SET(":=", 20),VAR("var", 21),IF("if", 22),THEN("then", 23),ELSE("else", 24),WHILE("while", 25),FOR("for", 26),BEGIN("begin", 27),WRITELN("writeln", 28),PROCEDURE("procedure", 29),END("end", 30),ERROR(UUID.randomUUID().toString(), 100);private String word;private Integer value;PL0(String word, Integer value) {this.word = word;this.value = value;}public String getWord() {return word;}public void setWord(String word) {this.word = word;}public Integer getValue() {return value;}public void setValue(Integer value) {this.value = value;}
}

Node实体类（key，value）

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.Getter;
import lombok.Setter;/*** @author HJC* @version 1.0* @apiNote Node类* @since 2021/11/6*/
@Data
@Getter
@Setter
@AllArgsConstructor
public class Node {String key;Integer value;@Overridepublic String toString() {return "(" + value + "," + key + ")";}
}

主实现类

import javax.swing.*;
import java.io.*;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;/*** @author HJC* @version 1.0* @apiNote PL0语言的词法分析器实现* @since 2021/11/6*/
public class Main {/*代码段索引*/private static Integer index = 0;/*代码段*/private static String progress;/*输出处理结果的链表*/public static List<Node> list = new LinkedList<>();/*存取单词总类的哈希表*/public static Map<String, Integer> map = new HashMap<>();public static void main(String[] args) throws IOException {// 初始化单词分类init();// 初始化代码initPL0();System.out.println(progress);// 消除注释没有写// 分析代码analyzer();}private static void analyzer() {while (index < progress.length()) {// 扫描字段Node node = scanner();if (node != null) {list.add(node);}}// 输出字段list.forEach(System.out::println);}/**  扫描一个单词出来**/private static Node scanner() {StringBuilder tokenBuilder = new StringBuilder();// 跳过一些特定字符while (progress.charAt(index) == ' ' || progress.charAt(index) == '\n' || progress.charAt(index) == '\t' || progress.charAt(index) == '\r') {index++;if (index >= progress.length()) {return null;}}// 字母开头if (Character.isLetter(progress.charAt(index))) {while (Character.isLetter(progress.charAt(index)) || Character.isDigit(progress.charAt(index)) || progress.charAt(index) == '_') {tokenBuilder.append(progress.charAt(index));index++;}String res = tokenBuilder.toString();// 关键字if (map.containsKey(res)) {return new Node("\"" + res + "\"", map.get(res));// 标识符} else {return new Node("\"" + res + "\"", PL0.IDENTIFIER.getValue());}}// 数字开头if (Character.isDigit(progress.charAt(index))) {boolean floatFlag = false;while (Character.isDigit(progress.charAt(index)) || progress.charAt(index) == '.') {if (!floatFlag && progress.charAt(index) == '.') {floatFlag = true;}if (floatFlag && progress.charAt(index) == '.') {throw new IllegalArgumentException("语法不正确");}tokenBuilder.append(progress.charAt(index));index++;}return new Node(tokenBuilder.toString(), PL0.INTEGER.getValue());}// 符号switch (progress.charAt(index)) {// 冒号case ':':if (progress.charAt(index + 1) == '=') {index += 2;//:=return new Node("\"" + PL0.SET.getWord() + "\"", PL0.SET.getValue());} else {// 单独的:index++;throw new IllegalArgumentException("语法不正确,:的意思是:=嘛?");}case '<':// <>if (progress.charAt(index + 1) == '>') {index += 2;return new Node("\"" + PL0.NE.getWord() + "\"", PL0.NE.getValue());}// <=if (progress.charAt(index + 1) == '=') {index += 2;return new Node("\"" + PL0.LE.getWord() + "\"", PL0.LE.getValue());}index++;return new Node("\"" + PL0.LT + "\"", PL0.LT.getValue());case '>':if (progress.charAt(index + 1) == '=') {index += 2;return new Node("\"" + PL0.GE.getWord() + "\"", PL0.GE.getValue());}index++;return new Node("\"" + PL0.GT.getWord() + "\"", PL0.GT.getValue());case '+':case '-':case '*':case '/':case '=':case ';':case ',':case '"':// 无特殊字段,直接返回String res = String.valueOf(progress.charAt(index++));return new Node("\"" + res + "\"", map.get(res));default:index++;return null;}}private static void init() {for (PL0 v : PL0.values()) {map.put(v.getWord(), v.getValue());}}private static void initPL0() throws IOException {/*选择一个文件JFrame jFrame = new JFrame();JFileChooser jFileChooser = new JFileChooser();jFileChooser.showOpenDialog(jFrame);String path = jFileChooser.getSelectedFile().getPath();*/String path = "D:\\HJC\\Desktop\\编译原理\\pl01.txt";BufferedReader reader = null;try {System.out.println(path);reader = new BufferedReader(new InputStreamReader(new FileInputStream(path)));String str;StringBuilder stringBuilder = new StringBuilder();while ((str = reader.readLine()) != null) {stringBuilder.append(str).append('\n');}progress = stringBuilder.toString();} catch (Exception e) {e.printStackTrace();} finally {if (reader != null) {reader.close();}}}
}

处理结果

procedure divide;
var w;
beginr := x; q := 0; w := y;
end(29,"procedure")
(1,"divide")
(17,";")
(21,"var")
(1,"w")
(17,";")
(27,"begin")
(1,"r")
(20,":=")
(1,"x")
(17,";")
(1,"q")
(20,":=")
(2,0)
(17,";")
(1,"w")
(20,":=")
(1,"y")
(17,";")
(30,"end")进程已结束，退出代码为 0