package com.siwanghu.syntaxanalyzer.bean;
public class Grammar {
private String left;
private String right;
private int id;
private static int ID = 0;
public Grammar() {
super();
id = ID++;
}
public Grammar(String left, String right) {
super();
this.left = left;
this.right = right;
id = ID++;
}
public String getLeft() {
return left;
}
public void setLeft(String left) {
this.left = left.replace(" ", "");
}
public String getRight() {
return right;
}
public void setRight(String right) {
this.right = right.replace(" ", "");
}
public int getId() {
return id;
}
@Override
public String toString() {
return "Grammar [left=" + left + ", right=" + right + "]";
}
}package com.siwanghu.syntaxanalyzer.algorithm;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import com.siwanghu.syntaxanalyzer.bean.Grammar;
public class Production {
private List productions = new LinkedList(); //产生式
private List symbols = new ArrayList(); //初始产生式非终结符
private List nonTerminatingSymbol = new ArrayList(); //LL(1)文法非终结符
private List terminatingSymbol = new ArrayList(); //LL(1)文法终结符
public Production(List productions) {
super();
this.productions = productions;
symbolProductions();
}
public List getProductions() {
return productions;
}
public List getSymbols() {
return symbols;
}
public List getNonTerminatingSymbol(){
return nonTerminatingSymbol;
}
public List getTerminatingSymbol(){
return terminatingSymbol;
}
public void removeLeftRecursion() {
for (int i = 0; i < symbols.size(); i++) {
for (int j = 0; j < i; j++) {
iterativeReplacement(symbols.get(i), symbols.get(j));
}
removeLeftRecursion(symbols.get(i));
}
no_or_is_terminatingSymbol();
}
private void symbolProductions() {
if (productions.size() != 0) {
for (int i = 0; i < productions.size(); i++) {
if (!((ArrayList) symbols).contains(productions
.get(i).getLeft().charAt(0))) {
symbols.add(productions.get(i).getLeft().charAt(0));
}
}
}
}
private void no_or_is_terminatingSymbol() {
for (int i = 0; i < productions.size(); i++) {
if (!((ArrayList) nonTerminatingSymbol)
.contains(productions.get(i).getLeft())) {
nonTerminatingSymbol.add(productions.get(i).getLeft());
}
if (productions.get(i).getLeft() == productions.get(i).getLeft()
.charAt(0)
+ "‘") {
nonTerminatingSymbol.add(productions.get(i).getLeft());
}
}
for (int i = 0; i < productions.size(); i++) {
String temp = productions.get(i).getRight();
temp = temp.replace("epsilon", "#");
for (int j = 0; j < nonTerminatingSymbol.size(); j++) {
temp = temp.replaceAll(nonTerminatingSymbol.get(j), "");
}
temp = temp.replaceAll("\\\\|", "");
temp = temp.replaceAll("‘", "");
char[] chars = temp.toCharArray();
for (int k = 0; k < chars.length; k++) {
if (chars[k] == ‘#‘) {
if (!terminatingSymbol.contains("epsilon")) {
terminatingSymbol.add("epsilon");
}
} else {
if (!terminatingSymbol.contains(String.valueOf(chars[k]))) {
terminatingSymbol.add(String.valueOf(chars[k]));
}
}
}
}
}
private void iterativeReplacement(Character left, Character right) {
ListIterator listIterator = productions.listIterator();
while (listIterator.hasNext()) {
String inRight = "";
Grammar grammar = listIterator.next();
if (grammar.getLeft().equals(left.toString())) {
boolean isReplacement = false;
String[] rights = grammar.getRight().split("\\\\|");
for (int i = 0; i < rights.length; i++) {
if (rights[i].startsWith(right.toString())) {
isReplacement = true;
}
}
if (isReplacement) {
ListIterator _listIterator = productions
.listIterator();
while (_listIterator.hasNext()) {
Grammar _grammar = _listIterator.next();
if (_grammar.getLeft().equals(right.toString())) {
String[] _rights = _grammar.getRight().split("\\\\|");
for (int i = 0; i < rights.length; i++) {
boolean isCheck = false;
if (rights[i].startsWith(right.toString())) {
isCheck = true;
for (int j = 0; j < _rights.length; j++) {
String temp = rights[i];
inRight += (temp.replaceFirst(
right.toString(), _rights[j]) + "|");
}
}
if (!isCheck) {
inRight += (rights[i] + "|");
}
}
}
}
if (inRight.length() != 0) {
listIterator.remove();
listIterator.add(new Grammar(left.toString(), inRight
.substring(0, inRight.length() - 1)));
}
}
}
}
}
private void removeLeftRecursion(Character left) {
ListIterator listIterator = productions.listIterator();
while (listIterator.hasNext()) {
Grammar grammar = listIterator.next();
if (grammar.getLeft().equals(left.toString())) {
String[] rights = grammar.getRight().split("\\\\|");
boolean isLeftRecursion = false;
for (int i = 0; i < rights.length; i++) {
if (rights[i].startsWith(left.toString())) {
isLeftRecursion = true;
}
}
if (isLeftRecursion) {
listIterator.remove();
String oneRight = "", twoRight = "";
for (int i = 0; i < rights.length; i++) {
if (!rights[i].startsWith(left.toString())) {
oneRight += (rights[i]
.concat(left.toString() + "‘") + "|");
} else {
twoRight += (rights[i].replaceFirst(
left.toString(), "").concat(
left.toString() + "‘") + "|");
}
}
listIterator.add(new Grammar(left.toString(), oneRight
.substring(0, oneRight.length() - 1)));
listIterator.add(new Grammar(left.toString() + "‘",
twoRight.concat("epsilon")));
}
}
}
}
@Override
public String toString() {
String temp = "非终结符: ";
for (int i = 0; i < nonTerminatingSymbol.size(); i++) {
temp += nonTerminatingSymbol.get(i) + " ";
}
temp+=" 共计:"+nonTerminatingSymbol.size();
temp += "\\n终结符: ";
for (int i = 0; i < terminatingSymbol.size(); i++) {
temp += terminatingSymbol.get(i) + " ";
}
temp+=" 共计:"+terminatingSymbol.size();
temp += "\\n消除左递归后的文法:\\n";
for (int i = 0; i < productions.size(); i++) {
temp += (productions.get(i) + "\\n");
}
return temp;
}
}
package com.siwanghu.syntaxanalyzer.test;
import java.util.LinkedList;
import java.util.List;
import com.siwanghu.syntaxanalyzer.algorithm.Production;
import com.siwanghu.syntaxanalyzer.bean.Grammar;
public class Test {
public static void main(String[] args) {
System.out.println("The Productions of G");
Grammar g1 = new Grammar("S", "Qc|c");
Grammar g2 = new Grammar("Q", "Rb|b");
Grammar g3 = new Grammar("R", "Sa|a");
List g_productions = new LinkedList();
g_productions.add(g3);
g_productions.add(g2);
g_productions.add(g1);
Production g_production = new Production(g_productions);
g_production.removeLeftRecursion();
System.out.print(g_production);
System.out.println("end G\\n");
System.out.println("The Productions of H");
Grammar h1 = new Grammar("E", "E+T|T");
Grammar h2 = new Grammar("T", "T*F|F");
Grammar h3 = new Grammar("F", "(E)|i");
List h_productions = new LinkedList();
h_productions.add(h1);
h_productions.add(h2);
h_productions.add(h3);
Production h_production = new Production(h_productions);
h_production.removeLeftRecursion();
System.out.print(h_production);
System.out.println("end H");
}
}本文出自 “胡思旺” 博客，请务必保留此出处http://siwanghu.blog.51cto.com/10630140/1716493
原文地址：http://siwanghu.blog.51cto.com/10630140/1716493
