栈应用——逆波兰式表达式的值

    /**
     * 给出一个逆波兰式，计算该表达式的值
     * @param s
     * @return
     */
    public int getTheValueOfRPN(String s) {
        char[] ch = s.toCharArray();
        Stack<Integer> stack = new Stack<Integer>();
        for(int i=0; i<ch.length; i++) {
            if(isOperator(ch[i])) {
                int v1 = stack.peek();
                stack.pop();
                int v2 = stack.peek();
                stack.pop();
                if(ch[i] == ‘+‘)
                    stack.push(v1 + v2);
                else if(ch[i] == ‘-‘)
                    stack.push(v1 - v2);
                else if(ch[i] == ‘*‘)
                    stack.push(v1 * v2);
                else 
                    stack.push(v1 / v2);
            }
            else 
                stack.push(Integer.valueOf(ch[i]-48));
            
        }
        return stack.pop();
    }

    private boolean isOperator(char c) {
        // TODO Auto-generated method stub
        if(c == ‘+‘ || c == ‘-‘ || c == ‘*‘ || c == ‘/‘)
            return true;
        return false;
    }