java - Postfix evaluation for multidigit numbers -

i programming postfix evaluator, , able correctly single digit number. need idea of how multiple digit number, current program evaluates 2 digit number different numbers.

here's code :

public class postfixevaluation {      public static void main(string[] args) {         string postfix = "23+79*-";          stack stack = new stack();          (int = 0; < postfix.length(); i++) {             if (postfix.charat(i) == '+') {                 int v1 = stack.pop();                 int v2 = stack.pop();                 stack.push(v2 + v1);             } else if (postfix.charat(i) == '-') {                 int v1 = stack.pop();                 int v2 = stack.pop();                 stack.push(v2 - v1);             } else if (postfix.charat(i) == '*') {                 int v1 = stack.pop();                 int v2 = stack.pop();                 stack.push(v2 * v1);             } else if (postfix.charat(i) == '/') {                 int v1 = stack.pop();                 int v2 = stack.pop();                 stack.push(v2 / v1);             } else if (postfix.charat(i) == '^') {                 int v1 = stack.pop();                 int v2 = stack.pop();                 stack.push((int) math.pow(v2, v1));             } else {                 stack.push((int) postfix.charat(i) - 48);             }         }         system.out.println(stack.pop());     }  } 

to able identify multi-digit numbers, there must separator symbol between 2 numbers.

for example, can use space separator symbol. tokens in postfix space separated. example become "2 3 + 7 9 * -". should read 1 token @ time, not 1 character.