package?第三章;
import?java.io.BufferedReader;
import?java.io.IOException;
import?java.io.InputStreamReader;
public?class?語法分析1?{
/*
?*?原始文法：
?*?
?*?E→E+T|E/T|T?
?*?T→T-F|T*F|F?
?*?F→(E)|i?
?*/
/*
?*?消除左遞歸
?*?
?*?E→TM?
?*?M→+TM|/TM|ε?
?*?T→FN?
?*?N→-FN|*FN|ε?
?*?F→(E)|i?
?*/
/*
?*?求First集和Follow集
?*?
?*?First(E)={(,i}? Follow(E)={),#}?
?*?First(T)={(,i}? Follow(T)={+,/,#}
?*?First(F)={(,i}? Follow(F)={-,*,#}?
?*?First(M)={+,/,ε}?Follow(M)={),#}
?*?First(N)={-,*,ε}?Follow(N)={+,/,#}
?*/
//?構(gòu)造預(yù)測分析表
private?String[]?Vt?=?{"+",?"/",?"-",?"*",?"(",?")",?"i"};
private?String[]?Vn?=?{"E",?"T",?"F",?"M",?"N"};
private?String[][]?M?=?{?
//+=0?? /=1? -=2?? *=3?? (=4?? )=5?? i=6?? #=7
{?"", "", "",? "",? "TM",? "",? "TM",? ""},?? //E=0
{?"", "",? "",? "",? "FN",? "",? "FN",? ""},?? //T=1
{?"", "",? "",? "",? "(E)",? "",? "i",? ""},?? //F=2
{?"+TM", "/TM",? "",? "",? "ε",? "",? "",? "ε"},?? //M=3
{?"ε",? "ε",? "-FN",? "*FN", "",? "",? "",? "ε"} //N=4
};
//開始分析
private?String[]?stack?=?new?String[256];
private?String?stack_top;
private?int?stack_ptr?=?-1;
private?int?ptr?=?0;
private?char?c_temp;
private?int?Vt_code;
private?int?Vn_code;
private?void?get_char(String?sentence){
c_temp?=?sentence.charAt(ptr);
ptr++;
if(c_temp?==?'+'){
Vt_code?=?0;
}else?if(c_temp?==?'/'){
Vt_code?=?1;
}else?if(c_temp?==?'-'){
Vt_code?=?2;
}else?if(c_temp?==?'*'){
Vt_code?=?3;
}else?if(c_temp?==?'('){
Vt_code?=?4;
}else?if(c_temp?==?')'){
Vt_code?=?5;
}else?if(c_temp?==?'i'){
Vt_code?=?6;
}else?if(c_temp?==?'#'){
Vt_code?=?7;
}
}
private?void?push(String?str){
stack_ptr++;
stack[stack_ptr]?=?str;
}
private?void?pull(){
stack_top?=?stack[stack_ptr];
stack[stack_ptr]?=?null;
stack_ptr--;
if(stack_top.equals("E")){
Vn_code?=?0;
}else?if(stack_top.equals("T")){
Vn_code?=?1;
}else?if(stack_top.equals("F")){
Vn_code?=?2;
}else?if(stack_top.equals("M")){
Vn_code?=?3;
}else?if(stack_top.equals("N")){
Vn_code?=?4;
}
}
private?boolean?isVt(String?str){
for(int?i?=?0;?i?<?Vt.length;?i++){
if(str.equals(Vt[i])){
return?true;
}
}
return?false;
}
private?boolean?isVn(String?str){
for(int?i?=?0;?i?<?Vn.length;?i++){
if(str.equals(Vn[i])){
return?true;
}
}
return?false;
}
public?boolean?SyntaxAnalyse(String?sentence){
push("#");
push("E");
get_char(sentence);
boolean?flag?=?true;
while(flag){
pull();
if(isVt(stack_top)){
if(stack_top.equals(String.valueOf(c_temp))){
get_char(sentence);
}else{
return?false;
}
}else?if(stack_top.equals("#")){
if(stack_top.equals(String.valueOf(c_temp))){
flag?=?false;
}else{
return?false;
}
}else?if(M[Vn_code][Vt_code]?!=?null){
if(!M[Vn_code][Vt_code].equals("ε")){
for(int?i?=?M[Vn_code][Vt_code].length()?-?1;?i?>=?0?;?i--){
push(String.valueOf(M[Vn_code][Vt_code].charAt(i)));
}
}
}else{
return?false;
}
}
return?true;
}
public?static?void?main(String[]?args)?throws?IOException{
while(true){
語法分析1?sa?=?new?語法分析1();
System.out.print("請(qǐng)輸入語句：");
BufferedReader?in?=?new?BufferedReader(new?InputStreamReader(System.in));?
String?str?=?in.readLine();
String?sentence?=?str?+?"#";?
boolean?result?=?sa.SyntaxAnalyse(sentence);
if(result?==?true){
System.out.println(str?+?"?是正確表達(dá)式！");
}else?if(result?==?false){
System.out.println(str?+?"?是錯(cuò)誤表達(dá)式！");
}else{
System.out.println("分析程序出現(xiàn)錯(cuò)誤！");
??????}??
}
}
}
懇請(qǐng)看得懂的大神給每行來個(gè)注釋，謝謝啦！
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