Write postfix solution in Java -


i'm writing postfix solution. can't tell why doesn't work , keep getting -1 on output. can please help? i'll include runner , runner , actual postfix class.

import java.util.stack; import java.util.scanner; import static java.lang.system.*;  public class postfixrunner { public static void main ( string[] args ) {     postfix test = new postfix("2 7 + 1 2 + +");     system.out.println(test.solve());      test.setexpression("1 2 3 4 + + +");     system.out.println(test.solve());      test.setexpression("9 3 * 8 / 4 +");     system.out.println(test.solve());      test.setexpression("3 3 + 7 * 9 2 / +");     system.out.println(test.solve());       test.setexpression("9 3 / 2 * 7 9 * + 4 -");     system.out.println(test.solve());       test.setexpression("5 5 + 2 * 4 / 9 +");     system.out.println(test.solve());      } }

and this...

import java.util.stack; import java.util.scanner; import static java.lang.system.*;  public class postfix { private stack<integer> stack; private string theexp;  public postfix() {  }  public postfix(string exp) {     theexp = exp;     stack = new stack<integer>(); }  public void setexpression(string exp) {     theexp= exp;     while (!stack.isempty()){         stack.pop();     } }  public int  calc(int two, int one, char current) {     int output;     switch(current){     case '*':         output=one*two;         break;     case '/':         output=one/two;         break;     case '+':         output=one+two;         break;     case '-':         output=one-two;         break;     default:         output=0;     }     return output; }  public int solve() {     (int i=0; i<theexp.length(); i++){         char current = theexp.charat(i);         int currentint = (int)character.digit(current, 10);         if (current!='*'||current!='/'||current!='+'||current!='-')             stack.push(currentint);         else             stack.push(calc(stack.pop(), stack.pop(), current));     }     return stack.pop(); }  public string tostring(){     return stack.tostring();     } }


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