java - How to split String using regex and insert into ArrayList? -

i trying build calculator converting infix postfix i've been having trouble handling cos, sin, , tan. current approach use regular expressions split input string cos, sin, etc , numbers placing them indexes of arraylist. have been able cos0 split 2 arraylist indexes, index that's supposed hold cos turns empty. don't know if using regular expressions wrong or if it's else.

import java.util.arraylist; import java.util.arrays; import java.util.scanner; import java.util.stack; import java.util.regex.matcher;    public class calculator {      //string sin = "sin";     //string cos = "cos";     //string tan = "tan";      public static void main(string[] args) {         new calculator().run();     }      public void run() {         calculator eval = new calculator();         scanner keyboard = new scanner(system.in);         system.out.println("please give equation.");          string input = keyboard.next();          system.out.print(eval.infixtopostfix(input));     }      public double infixtopostfix(string input)     {          stack<string>infixstack = new stack<>();         arraylist<string> exp = new arraylist<>(arrays.aslist(input.split("(cos|tan|sin\\d\\d)")));          string infix = "";          (int = 0; < exp.size(); i++)         {             if(exp.get(i).equals("")){                 continue;             }             if (exp.get(i).matches("([\\d])")) {                  infix = infix + exp.get(i);              }else if(exp.get(i).matches("([\\d])"))             {                 while(!infixstack.empty() && !infixstack.peek().matches("[\\(\\[\\{\\^]") && operatorpriority(infixstack.peek(), exp.get(i) ))                 {                     infix = infix + infixstack.peek();                     infixstack.pop();                 }                 infixstack.push(exp.get(i));             }else if(exp.get(i).matches("[(]"))             {                 infixstack.push(exp.get(i));             }else if(exp.get(i).matches("[)]"))             {                 while(!infixstack.empty() && !infixstack.peek().matches("[(]"));             {                 infix = infix + infixstack.peek();                 infixstack.pop();             }             infixstack.pop();             }else if(exp.get(i).matches("[\\^]"))             {                 infixstack.push(exp.get(i));             }else if(exp.get(i).matches("[\\[]"))             {                 infixstack.push(exp.get(i));             }else if(exp.get(i).matches("[\\]]"))             {                 while(!infixstack.empty() && !infixstack.peek().matches("[\\(\\[]"))                 {                     infix = infix + infixstack.peek();                     infixstack.pop();                 }                  infixstack.pop();             } else if(exp.get(i).matches("[\\{]"))             {                 infixstack.push(exp.get(i));             }else if(exp.get(i).matches("[\\}]"))             {                 while(!infixstack.empty() && !infixstack.peek().matches("[\\(\\{\\[]"))                 {                     infix = infix + infixstack.peek();                     infixstack.pop();                 }                 infixstack.pop();             }         }          while(!infixstack.empty())         {             infix = infix + infixstack.peek();             infixstack.pop();         }         return evaluatepostfix(infix);     }      public double evaluatepostfix(string infix) {         stack<double> equation = new stack<double>();         arraylist<string> postfixarray = new arraylist<>(arrays.aslist(infix.split("(?<=[\\w'(cos|tan|sin)'\\d])|(?=[\\w'(cos|tan|sin)'\\d])")));           double first;         double second;          try {             (int = 0; < postfixarray.size(); i++) {                 if (postfixarray.get(i).matches("([\\d])")) {                     double d = double.parsedouble(postfixarray.get(i));                     equation.push(d - '0');                 }else if(postfixarray.get(i).matches("([sin])"))                 {                     first = equation.pop();                     //second = equation.pop();                     double result = math.sin(math.toradians(first));                     equation.push(result);                 }else if(postfixarray.get(i).matches("([cos])"))                 {                     first = equation.pop();                     //second = equation.pop();                     double result = math.cos(math.toradians(first));                     equation.push(result);                 }else if(postfixarray.get(i).matches("([tan])"))                 {                     first = equation.pop();                     //second = equation.pop();                     double result = math.tan(math.toradians(first));                     equation.push(result);                 }                  if (postfixarray.get(i).matches("[*]")) {                     first = equation.pop();                     second = equation.pop();                     double result = first * second;                     equation.push(result);                 }                  if (postfixarray.get(i).matches("[/]")) {                     first = equation.pop();                     second = equation.pop();                     double result = second / first;                     equation.push(result);                 }                  if (postfixarray.get(i).matches("[+]")) {                     first = equation.pop();                     second = equation.pop();                     double result = first + second;                     equation.push(result);                 }                  if (postfixarray.get(i).matches("[-]")) {                     first = equation.pop();                     second = equation.pop();                     double result = first - second;                     equation.push(result);                 }                  if (postfixarray.get(i).matches("[(^)]")) {                     first = equation.pop();                     second = equation.pop();                     double result = math.pow(first, second);                     equation.push(result);                 }             }              if (!equation.isempty()) {                 return equation.pop();             } else                 return 0.0;         } catch (exception e ) {             return 0.0;         }     }      int operatorweight(string op)     {         int weight = 1;         if(op.equals("+") || op.equals("-"))         {             weight = 1;         }else if(op.equals("*") || op.equals("/") )         {             weight = 2;         }else if(op.equals("^"))         {             weight = 3;         }         return weight;     }      boolean operatorpriority(string operator1, string operator2)     {         int weight1 = operatorweight(operator1);         int weight2 = operatorweight(operator2);          if(weight1 == weight2)         {             return true;         }         return weight1 > weight2;     } } 

assuming following input format:

valid - cos49

invalid - cos43.54

invalid - sin(angle)

you can divide string 2 groups:

1. sin|cos|tan
2. digits

so regex should this:

pattern p = pattern.compile("(sin|cos|tan)|(\\d+)"); matcher m = p.matcher("cos60"); arraylist<string> = new arraylist<>(); while (m.find())     a.add(m.group(0));  system.out.println(a.tostring()); 

read how matcher class works. hope helps