java code to check if string is alphanumeric

To check if a string is alphanumeric in Java, you can use the matches method of the String class, along with a regular expression that matches alphanumeric characters.

Here is an example of how to check if a string is alphanumeric:

public class Main {
  public static void main(String[] args) {
    String str = "abc123";
    boolean isAlphanumeric = str.matches("^[a-zA-Z0-9]*$");
    System.out.println(isAlphanumeric);  // Outputs: true
  }
}

In this example, the matches method is used to check if the str string contains only alphanumeric characters. The regular expression "^[a-zA-Z0-9]*$" matches any combination of lowercase and uppercase letters and digits, and the ^ and $ characters anchor the match to the start and end of the string, respectively.

If the str string contains any non-alphanumeric characters, the matches method will return false. For example:

String str = "abc123!";
boolean isAlphanumeric = str.matches("^[a-zA-Z0-9]*$");
System.out.println(isAlphanumeric);  // Outputs: false

You can use a similar approach to check if a string is alphabetic (contains only letters) or numeric (contains only digits). For example, to check if a string is alphabetic:

String str = "abcdefg";
boolean isAlphabetic = str.matches("^[a-zA-Z]*$");
System.out.println(isAlphabetic);  // Outputs: true

And to check if a string is numeric:

String str = "12345";
boolean isNumeric = str.matches("^[0-9]*$");
System.out.println(isNumeric);  // Outputs: true