Stacks aStack = new Stacks();if (aStack.top == -1aStack.push(expression.get(position));((String) aStack.top()).equals("(")) {operator = (String) aStack.pop();&& aStack.top !while (aStack.top !op1 = (String) aStack.pop();op2 = (String) aStack.pop();aStack.push(Calculate.twoResult(is, op1, op2));if (operator.equals("+") || operator.equals("-")|| operator.equals("*") || operator.equals("/")|| operator.equals("(") || operator.equals