java判断是字符串

public class test {
    public static void main(String[] args) {
        String s = "225";
        s=s.concat("\n").concat("aaaaa");
        if (s != null && s.matches("^[0.0-9.0]+$"))  {// [0-9]没办法识别小数，[0.0-9.0]可以识别小数和整数
            System.out.println("输入是数字！");
            double num = Double.parseDouble(s);
            System.out.println(num);
        } else {
            System.out.println("输入值为字符！"+s);
        }
    }
}