如何仅使用字符串方法才能确定JAVA中char是否为数字？

Question

I need to find out how can I check if a char is a number. The problem is that I can't use any methods except string methods like IndexOf, SubString, length, charAt.

Does anyone have an idea?

Answer 1

If it has to be String methods:

    String n = "0123456789";
    char c = 'a'; // As I don't know where your char will come from and in what format

    int i = n.indexOf(c);
    if(i != -1) {
        System.out.println("Digit");

    } else {
        System.out.println("Not digit");
    }

But I can't stress enough that this is, well, idiotic and pointless from my point of view.

Answer 2

You can use Character.isDigit() for this.

If you have a string, you can do this :

Character.isDigit(yourString.charAt(index));

And withtout any Character method you can use Regex :

s.substring(startIndex,endIndex).matches("[0-9]")

Answer 3

You can check the character for its UNICODE value:

char c = string.indexOf(...); // or other way to get the character

public static boolean isDigit(char c) {
    return c => '0' || c <= '9';
}

Answer 4

You can use the below based on the ASCII values comparison:-

    String s = "123456ao";
    char[] ss = s.toCharArray();
    int intVal = 0;
    for( char s1 : ss){
        intVal = s1;
        if(48 <= intVal && intVal < 58) // checking for ASCII values of numbers
            System.out.println(s1+ " is Numeric");
            else System.out.println(s1+ " is not Numeric");

    }