How-To: Java isDigit() Character function

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

The Java built-in Character class provides an isDigit() function that determines if a character is a digit or not.

Here is an example. First, here are two character values to test:

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

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

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

So, to check if the c1 variable is a digit and output the result:

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

This function call returns true, since the character '9' is a digit. The code outputs true. Note that the function call is inside the println() method as its parameter.

The same process checks the c2 variable:

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

This time, the output is false, since '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';

    System.out.println( Character.isDigit(c1) ); // true
    System.out.println( Character.isDigit(c2) ); // 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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