Given a formula string to disassemble and calculate the result in Java

The requirements are simple, given a formula rule in the form of a string, disassembled with Java code, and the results can be computed.

Consider the number format "Integer, Decimal," in a string

? Consider the operator "+-*/()" in the string

? Consider the space, the arithmetic rule "divide by 0"

The following is the reference address, which contains the contents of the discussion section:

https://bbs.csdn.net/topics/380022283

Below is the Code section, which can be used as a tool class:

 Packagetest;Importjava.util.ArrayList;ImportJava.util.Comparator;Importjava.util.List;ImportJava.util.Stack;/*** Given formula string disassembly calculation *@authorKerala **/ Public classCalutil {Static FinalString symbol = "+-*/()";//operator    Static FinalString[] Priority = {"+-", "*/", "()"};//Operator Precedence         /*** Operator Comparator*/    StaticComparator<string> Comp =NewComparator<string>() {         Public intCompare (string s1, string s2) {intN1=0, n2=0;  for(inti=0; i<priority.length; i++) {                if(Priority[i].indexof (S1) >= 0) {N1 =i;} if(Priority[i].indexof (S2) >= 0) {N2 =i;} }            return(N1-n2);      }    }; /*** Input string formula, return result *@paramExp *@return   * @throwsException*/     Public StaticString getresultbystrcal (String exp)throwsexception{List<String> list = analyze (exp);//infix suffix        Doubleresult = CAcl (list);//Calculation Results        returnString.Format ("%.2f", result);//%.2f\n Explanation:%f--floating point type. 2--two-bit decimal point \n--line break    }    /*** Analysis Formula *@paramExp *@return     * @throwsException*/     Public Staticlist<string> analyze (String exp)throwsException {if(exp = =NULL) {            Throw NewException ("Illegal parameter."); } exp= Exp.replaceall ("\\s*", "");//Remove all spaces (to facilitate the existence of space in the middle of the legal)List<String> list =NewArraylist<string>(); Stack<String> sym =NewStack<string>(); StringBuilder buf=NewStringBuilder ();  for(CharC:exp.tochararray ()) {            if(Symbol.indexof (c) >= 0) {//if the operator                if(Buf.length () > 0) {//if there are operandsString v =buf.tostring (); if(! v.matches ("\\d+ ([.] \\d+)? ")) {                        Throw NewException ("Illegal varaible (" +v+ ").");                    } list.add (v); Buf.delete (0, Buf.length ()); }                if(c = = ' (') {Sym.push (string.valueof (c)); } Else if(c = = ') ') {String last= "";  while(Sym.size () > 0) { last=Sym.pop (); if(Last.equals ("(")) {                             Break; } Else{list.add (last); }                    }                    if(!" (". Equals (last)) {                        Throw NewException ("Illigal Express."); }                } Else if(Sym.size () > 0) {String s=string.valueof (c); String Last=Sym.peek (); if(Last.equals (") | | Comp.compare (S, last) > 0) {Sym.push (s); } Else{ Last=Sym.pop ();                        List.add (last);                    Sym.push (s); }                } Else{Sym.push (string.valueof (c)); }                     } Else{//not an operator is treated as an operand (because all spaces have been removed, it is no longer necessary to determine the space)Buf.append (c); }        }        if(Buf.length () > 0) {List.add (buf.tostring ()); }         while(Sym.size () > 0) {String last=Sym.pop (); if("()". IndexOf (last) >= 0) {                Throw NewException ("Illigal Express.");        } list.add (last); }                returnlist; }    /*** Calculation *@paramlist *@return     * @throwsException*/     Public Static DoubleCAcl (list<string> List)throwsException {Stack<Double> val =NewStack<double>(); Doubleresult = 0;  while(List.size () > 0) {String s= List.remove (0); if(Symbol.indexof (s) >= 0) {                DoubleD1 =Val.pop (); DoubleD2 =Val.pop (); if("+". Equals (s)) {Result= D2 +D1; } Else if("-". Equals (s)) {Result= D2-D1; } Else if("*". Equals (s)) {Result= D2 *D1; } Else if("/". Equals (s)) {Result= D2/D1; } Else {                    Throw NewException ("Illigal symbol" ("+s+"). ");            } val.push (Result); } Else {                if(!s.matches ("\\d+ ([.] \\d+)? ")) {                    Throw NewException ("Illigal variable (" +s+ ").");            } Val.push (Double.valueof (s)); }        }                returnresult; }    }

Test it:

 Packagetest;/*** Test Split string formula operation *@authorKerala **/ Public classtestcal {/**     * @paramargs *@throwsException*/     Public Static voidMain (string[] args) {String exp= "2.5*0.4+ (2*5)"; Try{String result=calutil.getresultbystrcal (exp);        System.out.printf (result); } Catch(Exception e) {e.printstacktrace (); System.out.println ("Please enter the correct calculation formula"); }            }}

Currently testing a few formulas, are also correct, if there are problems, then add!

Given a formula string to disassemble and calculate the result in Java