How-To: Java isDigit() function

Sometimes it is helpful to know if a character is a digit (0-9) or not.

The built-in Java Character class provides an isDigit() function that determines if a character is a digit or not. If it is, the function returns true. Otherwise, it returns false.

Here is an example. Declare and populate some character values to test:

char c1 = '9';
char c2 = 'A';

The c1 variable contains a character value that is a digit. The c2 variable contains a character value that is not a digit.

To invoke the isDigit() function, use the Character class and pass in the character to test as the parameter. The return value of the function is a Boolean (true or false) value.

This statement checks if the c1 variable contains a digit and stores the result in a Boolean variable b1:

boolean b1 = Character.isDigit(c1);

Since the character '9' is a digit, the statement assigns true to b1.

The same process checks the c2 variable:

b1 = Character.isDigit(c2);

This time, the program assigns false to b1, because 'A' is not a digit.

Here is the complete program:

public class Example {
  public static void main(String[] args) throws Exception {

    char c1 = '9';
    char c2 = 'A';

    boolean b1 = Character.isDigit(c1);
    System.out.println(b1); // true

    b1 = Character.isDigit(c2);
    System.out.println(b1); // false
  }
}

The Character.isDigit() function is very useful when determining if a character is a digit or not. This can help with a variety of string processing tasks in the programs you write.

Thanks for reading. 😃

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