Java Data Type How to - Check if a character is a Letter or digit

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Question

We would like to know how to check if a character is a Letter or digit.

Answer

isDigit(): true if the argument is a digit (0 to 9), and false otherwise.

public class MainClass {
  public static void main(String[] args) {
    char symbol = 'A';
/*w  w w  .  j  a  v a  2s . co m*/
    if (Character.isDigit(symbol)) {
      System.out.println("true");
    }else{
      System.out.println("false");
    }
  }
}

Validate if a String contains only numbers

public class Main {
  public static boolean containsOnlyNumbers(String str) {
    for (int i = 0; i < str.length(); i++) {
      if (!Character.isDigit(str.charAt(i)))
        return false;
    }/*from   ww w  .  j av  a  2 s.com*/
    return true;
  }

  public static void main(String[] args) {
    System.out.println(containsOnlyNumbers("123456"));
    System.out.println(containsOnlyNumbers("123abc456"));
  }
}

The code above generates the following result.

isLetterOrDigit(): true if the argument is a letter or a digit, and false otherwise.

public class MainClass {
  public static void main(String[] args) {
    char symbol = 'A';
/*from w  w  w.j a  v  a  2 s. com*/
    if (Character.isLetterOrDigit(symbol)) {
      System.out.println("true");
    }else{
      System.out.println("false");
    }
  }
}

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