如何确定字符串是否具有非字母数字字符？

Question

I need a method that can tell me if a String has non alphanumeric characters.

For example if the String is "abcdef?" or "abcdefà", the method must return true.

Answer 1

Using Apache Commons Lang:

!StringUtils.isAlphanumeric(String)

Alternativly iterate over String's characters and check with:

!Character.isLetterOrDigit(char)

You've still one problem left: Your example string "abcdefà" is alphanumeric, since à is a letter. But I think you want it to be considered non-alphanumeric, right?!

So you may want to use regular expression instead:

String s = "abcdefà";
Pattern p = Pattern.compile("[^a-zA-Z0-9]");
boolean hasSpecialChar = p.matcher(s).find();

Answer 2

One approach is to do that using the String class itself. Let's say that your string is something like that:

String s = "some text";
boolean hasNonAlpha = s.matches("^.*[^a-zA-Z0-9 ].*$");

one other is to use an external library, such as Apache commons:

String s = "some text";
boolean hasNonAlpha = !StringUtils.isAlphanumeric(s);

Answer 3

You have to go through each character in the String and check Character.isDigit(char); or Character.isletter(char);

Alternatively, you can use regex.

Answer 4

Use this function to check if a string is alphanumeric:

public boolean isAlphanumeric(String str)
{
    char[] charArray = str.toCharArray();
    for(char c:charArray)
    {
        if (!Character.isLetterOrDigit(c))
            return false;
    }
    return true;
}

It saves having to import external libraries and the code can easily be modified should you later wish to perform different validation checks on strings.

Answer 5

string.matches("^\\\\W*$"); should do what you want, but it does not include whitespace. string.matches("^(?:\\\\W|\\\\s)*$"); does match whitespace as well.

Answer 6

如果您可以使用 Apache Commons 库，那么 Commons-Lang StringUtils有一个名为isAlphanumeric()的方法isAlphanumeric()您的需求。

Answer 7

You can use isLetter(char c) static method of Character class in Java.lang .

public boolean isAlpha(String s) {
    char[] charArr = s.toCharArray();

    for(char c : charArr) {
        if(!Character.isLetter(c)) {
            return false;
        }
    }
    return true;
}

Answer 8

虽然它不适用于数字，但您可以检查小写和大写值是否相同，对于非字母字符，它们将相同，您应该在此之前检查数字以获得更好的可用性