Java Data Type - 如何检查字符串是否表示浮点数

public class Main {

  public static void main(String[] args) {
    System.out.println(testNumber("2.2"));
  }

  public static Float testNumber(String aArg) {
    while (true) {
      if (aArg.length() == 0) {
        return null;
      }
      if (aArg.matches("-?\\d+(\\.\\d+)?") == true) {
        break;
      } else {
        throw new IllegalArgumentException("not a number");
      }
    }
    return Float.parseFloat(aArg);
  }
}