Determine whether an expression is written as a proposition formula Java

1 ImportJava.util.Scanner;2 3  Public classExpress {4          Public Static voidMain (string[] args)throwsexception{5System.out.println ("Please Enter expression:");6Scanner exp =NewScanner (system.in);7String expressnew =exp.nextline ();8             9             BooleanAnswer =Verify (expressnew);Ten              One             if(Answer = =true){ ASystem.out.println ("This expression is a proposition formula. "); -             } -             ElseSystem.out.println ("This expression is not a proposition formula. "); the Exp.close ();  -         } -          -          Public Static BooleanVerify (String exp) { +             inti,j; -             Charsign1,sign2; + String exp1,exp2; A              ati =exp.length (); -             //Single character -             if(i = = 1){ -SIGN1 = Exp.charat (i-1); -                 if(Sign1 >= ' a ' && sign1 <= ' z ' | | sign1 >= ' a ' && sign1 <= ' z '){ -                     return true; in                 } -                 Else return false; to             } +             if(I ==2 ){ -SIGN1 = Exp.charat (0); theSIGN2 = Exp.charat (1); *                 if(Sign1 = = '! ' && (sign2 >= ' a ' && sign2 <= ' z ' | | sign2 >= ' a ' && sign2 <= ' z ' )){ $                     return true;Panax Notoginseng                 } -                 Else return false; the             } +             if(i = = 3){ A                 if(Exp.charat (0) = = ' (' && exp.charat (2) = = ') '){ the                     returnVerify (String.valueof (Exp.charat (1))); +                 } -                 Else if(Exp.charat (1) = = ' & ' | | Exp.charat (1) = = ' | ' | | Exp.charat (1) = = ' ~ '){ $                     returnVerify (string.valueof (Exp.charat (0)) &&verify (String.valueof (Exp.charat (2))); $                 } -                 Else{ -                     return false; the                 } -             }Wuyi             if(I >= 4)//the length of the formula cannot be 2 and 3, so it is judged directly from a string of length 4 the             {  -                 if((Exp.charat (0) = = ' (') && (Exp.charat (i-1) = = ') '))//when the first and last symbol of a string is ' (' and ') ', it is possible that a formula Wu                 {    -                     if(Exp.charat (1) = = '! ')//when the second symbol is a negative sign, the case About                     {    $EXP1 = exp.substring (2, i-1);//take out the substring of the string sub1, recursively determine whether it is a formula -                         if(Verify (EXP1)) { -                             return true;  -}Else {    A                             return false;  +                         }    the}Else if(Exp.charat (1) = = ' (')//when the second symbol is ' (' the condition of the symbol -                     {    $j = Find (exp, 1, i-2);//Find (String,int,int) is used to determine the location of the ' (' matching ') ' the                         if(j==-1 | | j = = I-2 | | j = i-3) {//after matching the parentheses, you must leave two characters behind.  the                             return false;  the}Else {    theEXP1 = exp.substring (1, j+1);  -EXP2 = exp.substring (j + 2, i-1);  in         the                             if((Exp.charat (j + 1) = = ' & ' | | Exp.charat (j) = = ' | ' | | Exp.charat (1) = = ' ~ ')    the&& Verify (EXP1) &&Verify (EXP2)) {     About                                 return true;  the}Else {    the                                 return false;  the                             }    +                         }    -}Else if(Exp.charat (1) >= ' a ' && exp.charat (1) <= ' Z ' | | exp.charat (1) >= ' a ' && exp.charat (1) <= ' z ')//when the second symbol is atomic, take the remaining part the{//Divided into sub1, judge whether Sub2 is a formula,Bayi                         if(i = = 4) {    the                             return false;//This situation must be greater than or equal to 5 the}Else {    -                             if(Exp.charat (2) = = ' & ' | | Exp.charat (2) = = ' | ' | | Exp.charat (1) = = ' ~ ')//The string is the formula -                             {    theEXP1 = exp.substring (3, I-1);  the                                 if(Verify (EXP1)) { the                                     return true;  the}Else {    -                                     return false;  the                                 }    the}Else {    the                                 return false; 94                             }    the                         }    the}Else {    the                         return false; 98                     }    About}Else {    -                     return false; 101}//End >=4102}Else {   103                 return false;//Strings of other lengths and strings of other cases are not formulas104             }    the         }   106        107          Public Static intFind (String s,intBeginintend) {   108             intN1 = 0, N2 = 0, i =begin; 109              while(I <=end) {   the                 if(S.charat (i) = = ' (')   111n1++;  the                 Else if(S.charat (i) = = ') ')   113n2++;  the                 Else{    the                 }              the                 if(N1 = =n2)117                      Break; 118i++; 119             }    -             if(I > Begin && I <=end)121                 returni; 122             Else   123                 return-1; 124         }    the         126}

Determine whether an expression is written as a proposition formula Java