Character.isDigit() 错误：找不到适合 isDigit(String) 的方法

Question

Kepp getting an error when using Character.isDigit()

I've looked it up elsewhere and tested it fine there but I keep running into this error here.

  Scanner scnr = new Scanner(System.in);
  boolean hasDigit;
  String passCode;

  hasDigit = false;
  passCode = scnr.next();

  hasDigit = Character.isDigit(passCode);

  if (hasDigit) {
     System.out.println("Has a digit.");
  }
  else {
     System.out.println("Has no digit.");
  }

Expect true or false depending on scanner input. Keep getting this error thrown at me:

CheckingPasscodes.java:12: error: no suitable method found for isDigit(String)
  hasDigit = Character.isDigit(passCode);
                      ^
method Character.isDigit(char) is not applicable
  (argument mismatch; String cannot be converted to char)
method Character.isDigit(int) is not applicable
  (argument mismatch; String cannot be converted to int)

Answer 1

The method Character.isDigit() takes a char as input - you are trying to pass it a String .

The error described what the problem is:

argument mismatch; String cannot be converted to char

Answer 2

The Scanner.next method will return whole tokens (usually words) from the input stream. These words are Strings. The Character.isDigit function requires a char as input, not a String.

You could loop over the word, get each letter as a char and test them:

for (int i = 0; i < passCode.length(); i++){
    char c = passCode.charAt(i);
    if (Character.isDigit(c)) {
        hasDigit = true;
    }
}

Answer 3

The error is that hasDigit = Character.isDigit(passCode); Character.isDigit() expects a character as an argument but you passing String. So correct this convert the String to char. you can try

     Scanner scnr = new Scanner(System.in);
  boolean hasDigit;
  char passCode;

  hasDigit = false;
  passCode =  scnr.next().charAt(0);

  hasDigit = Character.isDigit(passCode);

  if (hasDigit) {
     System.out.println("Has a digit.");
  }

  else {
     System.out.println("Has no digit.");
  }

Answer 4

I found this worked for me. I set each specified index in the string to a character value using charAt(). From there I created an if statement that would set hasDigit to true if any of the char variables had a number, using Character.isDigit() enter image description here