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What is the best way to tell if a character is a letter or number in Java without using regexes?

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How do you check if a character is a letter or number in Java?

We can check whether the given character in a string is a number/letter by using isDigit() method of Character class. The isDigit() method is a static method and determines if the specified character is a digit.

How do you identify a letter in Java?

In order to check if a String has only Unicode letters in Java, we use the isDigit() and charAt() methods with decision-making statements. The isLetter(int codePoint) method determines whether the specific character (Unicode codePoint) is a letter. It returns a boolean value, either true or false.

How do you check if a string is not a letter?

To check if String contains only alphabets in Java, call matches() method on the string object and pass the regular expression "[a-zA-Z]+" that matches only if the characters in the given string is alphabets (uppercase or lowercase).


Character.isDigit(string.charAt(index)) (JavaDoc) will return true if it's a digit
Character.isLetter(string.charAt(index)) (JavaDoc) will return true if it's a letter


As the answers indicate (if you examine them carefully!), your question is ambiguous. What do you mean by "an A-z letter" or a digit?

  • If you want to know if a character is a Unicode letter or digit, then use the Character.isLetter and Character.isDigit methods.

  • If you want to know if a character is an ASCII letter or digit, then the best thing to do is to test by comparing with the character ranges 'a' to 'z', 'A' to 'Z' and '0' to '9'.

Note that all ASCII letters / digits are Unicode letters / digits ... but there are many Unicode letters / digits characters that are not ASCII. For example, accented letters, cyrillic, sanskrit, ...


The general solution is to do this:

Character.UnicodeBlock block = Character.UnicodeBlock.of(someCodePoint);

and then test to see if the block is one of the ones that you are interested in. In some cases you will need to test for multiple blocks. For example, there are (at least) 4 code blocks for Cyrillic characters and 7 for Latin. The Character.UnicodeBlock class defines static constants for well-known blocks; see the javadocs.

Note that any code point will be in at most one block.


I'm looking for a function that checks only if it's one of the Latin letters or a decimal number. Since char c = 255, which in printable version is and considered as a letter by Character.isLetter(c). This function I think is what most developers are looking for:

private static boolean isLetterOrDigit(char c) {
    return (c >= 'a' && c <= 'z') ||
           (c >= 'A' && c <= 'Z') ||
           (c >= '0' && c <= '9');
}

Java Character class has an isLetterOrDigit method since version 1.0.2


I don't know about best, but this seems pretty simple to me:

Character.isDigit(str.charAt(index))
Character.isLetter(str.charAt(index))

// check if ch is a letter
if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
    // ...

// check if ch is a digit
if (ch >= '0' && ch <= '9')
    // ...

// check if ch is a whitespace
if ((ch == ' ') || (ch =='\n') || (ch == '\t'))
    // ...

Source: https://docs.oracle.com/javase/tutorial/i18n/text/charintro.html


Use the below code

Character.isLetterOrDigit(string.charAt(index))