您可以使用正则表达式进行检查.

You can check this with a regex.

假设(仅数字值):

String a = "493284835";
a.matches("^[0-9]+$"); // returns true

假设(仅字母数字值):

Suppose that (alphanumeric values only):

String a = "dfdf4932fef84835fea";
a.matches("^([A-Za-z]|[0-9])+$"); // returns true

正如Pangea在评论区所说:

As Pangea said in the comments area :

如果性能至关重要，则***编译正则表达式.参见下面的示例:

If the performance are critical, it's preferrable to compile the regex. See below for an example :

String a = "dfdf4932fef84835fea";
Pattern pattern = Pattern.compile("^([A-Za-z]|[0-9])+$");
Matcher matcher = pattern.matcher(a);

if (matcher.find()) {
    // it's ok
}