Java Check if String is Alphanumeric using Regular Expression (RegEx)

A String is said to be alphanumeric if,

• It contains lowercase alphabets from 'a' to 'z'.
• It contains uppercase alphabets from 'A' to 'Z'.
• It contains digits from '0' to '9'.
• It does not contain any special characters, punctuation marks, or spaces.
• The string may contain a combination of lowercase letters, uppercase letters, and digits in any order.
• The length of the string can be any positive integer, including zero (empty string).

Examples:

String	Validity
"abc123"	Valid
"HelloWorld"	Valid
"123456"	Valid
"AbCdEfG"	Valid
"aBc123"	Valid
"a1b2c3"	Valid
"Alphanumeric123"	Valid
"Invalid String!"	Invalid
"Spaces Are NotAllowed"	Invalid
"Special@Characters"	Invalid
"123_456"	Invalid
""	Valid

Now that we know what Alphanumerics are, let's take an example using Java RegEx.

package org.code2care.examples;

import java.util.Arrays;
import java.util.List;
import java.util.regex.Pattern;

public class AlphanumericRegExValidation {

    public static void main(String[] args) {

        List<String> strings = Arrays.asList(
                "abc123",
                "HelloWorld",
                "123456",
                "AbCdEfG",
                "aBc123",
                "a1b2c3",
                "Alphanumeric123",
                "Invalid String!",
                "Spaces Are NotAllowed",
                "Special@Characters",
                "123_456",
                ""
        );

        Pattern pattern = Pattern.compile("^[a-zA-Z0-9]+$");

        for (String str : strings) {
            boolean isValid = pattern.matcher(str).matches();
            System.out.println("String: " + str + " is Alphanumeric: " + isValid);
        }
    }
}

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