编译原理实验——词法分析

Kovic_99

已于 2025-04-15 08:55:30 修改

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分类专栏：数值分析文章标签： java 开发语言

于 2024-06-25 09:47:27 首次发布

本文链接：https://blog.youkuaiyun.com/qq_54375829/article/details/139939467

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目的与要求

通过完成LL(1)语法分析程序分析和调试，了解自顶向下语法分析的思路，熟悉判断LL (1)文法的方法，学会构造LL(1)文法的预测分析表以及对某一个输入串的分析过程。本实验在培养编程能力的同时培养自主学习和团队协作能力。

实验内容

从键盘读入要分析的文法，并判断正误;若无误，由程序自动构造FIRST、FOLLOW 集以及SELECT集合，判断是否为LL (1)文法;

分析的文法为G[E]：（0）E→ TE’ （1）E’→ +TE’ （2）E’→ε （3）T→ FT’

（4）T’→ *FT’ （5）T’→ε （6）F→ (E) （7）F→a

若符合LL (1)文法，由程序自动构造LL (1)分析表;
由算法判断给定的输入符号串a*(a+a)是否为该文法的句型。

/**

* Created by kovic on 2023/4/26.

* Use IntelliJ IDEA 2022.2.2

import java.util.*;

public class LL1 {

public static void main(String[] args) {

Test test = new Test();

test.getNvNt();

test.Init();

test.createTable();

test.ouput();

System.out.println("");

test.analyzeLL();

}

class Test {

public HashMap<Character, HashSet<Character>> firstSet = new HashMap<Character, HashSet<Character>>();

public HashMap<String, HashSet<Character>> firstSetX = new HashMap<String, HashSet<Character>>();

public Character S = 'E';

public HashMap<Character, HashSet<Character>> followSet = new HashMap<Character, HashSet<Character>>();

public HashSet<Character> VnSet = new HashSet<Character>();

public HashSet<Character> VtSet = new HashSet<Character>();

public HashMap<Character, ArrayList<String>> experssionSet = new HashMap<Character, ArrayList<String>>();

public String[][] table;

public Stack<Character> analyzeStatck = new Stack<Character>();

public String strInput = "a*(a+a)$";

public String action = "";

int index = 0;

Scanner scanner = new Scanner(System.in);

public String[] inputExperssion={};

public void Init() {

for (String e : inputExperssion) {

String[] str = e.split("->");

char c = str[0].charAt(0);

ArrayList<String> list = experssionSet.containsKey(c) ? experssionSet.get(c) : new ArrayList<String>();

list.add(str[1]);

experssionSet.put(c, list);

}

for (Character c : VnSet)

getFirst(c);

for (Character c : VnSet) {

ArrayList<String> l = experssionSet.get(c);

for (String s : l)

getFirst(s);

}

getFollow(S);

for (Character c : VnSet) {

getFollow(c);

}

public void getNvNt() {

System.out.println("注意：@ 为空， E‘->K T'->M");

System.out.print("请输入文法产生式的个数：");

int num =scanner.nextInt();

inputExperssion=new String[num];

System.out.println("请输入文法的"+num+"个产生式，并以回车分割每个产生式：");

for(int i=0;i<num;i++){

System.out.print("第"+ (i) +"个：");

inputExperssion[i]= scanner.next();

}

for (String e : inputExperssion) {

String[] str = e.split("->");

VnSet.add(str[0].charAt(0));

}

for (String e : inputExperssion) {

String[] str = e.split("->");

String right = str[1];

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

if (!VnSet.contains(right.charAt(i)))

VtSet.add(right.charAt(i));

}

public void getFirst(Character c) {

ArrayList<String> list = experssionSet.get(c);

HashSet<Character> set = firstSet.containsKey(c) ? firstSet.get(c) : new HashSet<Character>();

// c为终结符直接添加

if (VtSet.contains(c)) {

set.add(c);

firstSet.put(c, set);

return;

}

// c为非终结符处理其每条产生式

for (String s : list) {

// c 推出空串直接添加

if (s == Character.toString('@')) {

set.add('@');

}

// X -> Y1Y2Y3… 情况

else {

// 从左往右扫描生成式右部

int i = 0;

while (i < s.length()) {

char tn = s.charAt(i);

//先处理防止未初始化

getFirst(tn);

HashSet<Character> tvSet = firstSet.get(tn);

// 将其first集加入左部

for (Character tmp : tvSet)

set.add(tmp);

// 若包含空串处理下一个符号

if (tvSet.contains('@'))

i++;

// 否则退出处理下一个产生式

else

break;

}

firstSet.put(c, set);

}

public void getFirst(String s) {

HashSet<Character> set = (firstSetX.containsKey(s)) ? firstSetX.get(s) : new HashSet<Character>();

// 从左往右扫描该式

int i = 0;

while (i < s.length()) {

char tn = s.charAt(i);

HashSet<Character> tvSet = firstSet.get(tn);

// 将其非空 first集加入左部

for (Character tmp : tvSet)

if (tmp != '@')

set.add(tmp);

// 若包含空串处理下一个符号

if (tvSet.contains('@'))

i++;

// 否则结束

else

break;

// 到了尾部即所有符号的first集都包含空串把空串加入

if (i == s.length()) {

set.add('@');

}

firstSetX.put(s, set);

}

public void getFollow(char c) {

ArrayList<String> list = experssionSet.get(c);

HashSet<Character> setA = followSet.containsKey(c) ? followSet.get(c) : new HashSet<Character>();

//如果是开始符添加 $

if (c == S) {

setA.add('$');

}

//查找输入的所有产生式，确定c的后跟终结符

for (Character ch : VnSet) {

ArrayList<String> l = experssionSet.get(ch);

for (String s : l)

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

if (s.charAt(i) == c && i + 1 < s.length() && VtSet.contains(s.charAt(i + 1)))

setA.add(s.charAt(i + 1));

}

followSet.put(c, setA);

//处理c的每一条产生式

for (String s : list) {

int i = s.length() - 1;

while (i >= 0) {

char tn = s.charAt(i);

//只处理非终结符

if (VnSet.contains(tn)) {

// 都按 A->αBβ 形式处理

//若β不存在 followA 加入 followB

//若β存在，把β的非空first集加入followB

//若β存在且 first(β)包含空串 followA 加入 followB

//若β存在

if (s.length() - i - 1 > 0) {

String right = s.substring(i + 1);

//非空first集加入 followB

HashSet<Character> setF = null;

if (right.length() == 1) {

if (!firstSet.containsKey(right.charAt(0)))

getFirst(right.charAt(0));

setF = firstSet.get(right.charAt(0));

} else {

//先找出右部的first集

if (!firstSetX.containsKey(right))

getFirst(right);

setF = firstSetX.get(right);

}

HashSet<Character> setX = followSet.containsKey(tn) ? followSet.get(tn) : new HashSet<Character>();

for (Character var : setF)

if (var != '@')

setX.add(var);

followSet.put(tn, setX);

// 若first(β)包含空串 followA 加入 followB

if (setF.contains('@')) {

if (tn != c) {

HashSet<Character> setB = followSet.containsKey(tn) ? followSet.get(tn) : new HashSet<Character>();

for (Character var : setA)

setB.add(var);

followSet.put(tn, setB);

}

//若β不存在 followA 加入 followB

else {

// A和B相同不添加

if (tn != c) {

HashSet<Character> setB = followSet.containsKey(tn) ? followSet.get(tn) : new HashSet<Character>();

for (Character var : setA)

setB.add(var);

followSet.put(tn, setB);

}

i--;

}

//如果是终结符往前看如 A->aaaBCDaaaa 此时β为 CDaaaa

else i--;

}

public void createTable() {

Object[] VtArray = VtSet.toArray();

Object[] VnArray = VnSet.toArray();

// 预测分析表初始化

table = new String[VnArray.length + 1][VtArray.length + 1];

table[0][0] = "Vn/Vt";

//初始化首行首列

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

table[0][i + 1] = (VtArray[i].toString().charAt(0) == '@') ? "$" : VtArray[i].toString();

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

table[i + 1][0] = VnArray[i] + "";

//全部置error

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

for (int j = 0; j < VtArray.length; j++)

table[i + 1][j + 1] = "error";

//插入生成式

for (char A : VnSet) {

ArrayList<String> l = experssionSet.get(A);

for (String s : l) {

HashSet<Character> set = firstSetX.get(s);

for (char a : set)

insert(A, a, s);

if (set.contains('@')) {

HashSet<Character> setFollow = followSet.get(A);

if (setFollow.contains('$'))

insert(A, '$', s);

for (char b : setFollow)

insert(A, b, s);

}

public void analyzeLL() {

System.out.println("****************LL分析过程**********");

System.out.println(" Stack Input Action");

analyzeStatck.push('$');

analyzeStatck.push('E');

displayLL();

char X = analyzeStatck.peek();

while (X != '$') {

char a = strInput.charAt(index);

if (X == a) {

action = "match " + analyzeStatck.peek();

analyzeStatck.pop();

index++;

} else if (VtSet.contains(X))

return;

else if (find(X, a).equals("error"))

return;

else if (find(X, a).equals("@")) {

analyzeStatck.pop();

action = X + "->@";

} else {

String str = find(X, a);

if (str != "") {

action = X + "->" + str;

analyzeStatck.pop();

int len = str.length();

for (int i = len - 1; i >= 0; i--)

analyzeStatck.push(str.charAt(i));

} else {

System.out.println("error at '" + strInput.charAt(index) + " in " + index);

return;

}

X = analyzeStatck.peek();

displayLL();

}

System.out.println("该文法符合LL（1）文法");

System.out.println("****************LL分析过程**********");

}

public String find(char X, char a) {

for (int i = 0; i < VnSet.size() + 1; i++) {

if (table[i][0].charAt(0) == X)

for (int j = 0; j < VtSet.size() + 1; j++) {

if (table[0][j].charAt(0) == a)

return table[i][j];

}

return "";

}

public void insert(char X, char a, String s) {

if (a == '@') a = '$';

for (int i = 0; i < VnSet.size() + 1; i++) {

if (table[i][0].charAt(0) == X)

for (int j = 0; j < VtSet.size() + 1; j++) {

if (table[0][j].charAt(0) == a) {

table[i][j] = s;

return;

}

public void displayLL() {

// 输出 LL1

Stack<Character> s = analyzeStatck;

System.out.printf("%23s", s);

System.out.printf("%13s", strInput.substring(index));

System.out.printf("%10s", action);

System.out.println();

}

public void ouput() {

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

for (Character c : VnSet) {

HashSet<Character> set = firstSet.get(c);

System.out.printf("%10s", c + " -> ");

for (Character var : set)

System.out.print(var);

System.out.println();

}

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

System.out.println("");

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

for (Character c : VnSet) {

HashSet<Character> set = followSet.get(c);

System.out.print("Follow " + c + ":");

for (Character var : set)

System.out.print(var);

System.out.println();

}

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

System.out.println("");

System.out.println("**********LL1预测分析表********");

for (int i = 0; i < VnSet.size() + 1; i++) {

for (int j = 0; j < VtSet.size() + 1; j++) {

System.out.printf("%6s", table[i][j] + " ");

}

System.out.println();

}

System.out.println("**********LL1预测分析表********");

}

结果分析（包括实验结果截图）

实验结果分析：经分析，文法G[E]符合LL(1)文法，且给定的输入符号串a*(a+a)是该文法的句型。