public class Postfix {

// example of using a stack

public static void main(String[] args) {

Stack<Integer> stacky = new Stack<>();

for (char ch : "123+45*6-+-".toCharArray()) {

if (ch == '+')

stacky.push(stacky.pop() + stacky.pop());

else if (ch == '*')

stacky.push(stacky.pop() * stacky.pop());

else if (ch == '-')

stacky.push(-stacky.pop() + stacky.pop());

else

stacky.push(ch-'0');

}

System.out.println(stacky.pop());

}

}