Checking if a string contains only digits ? (isDigitMethod required)

Question

The user should give a string, where we should check if all characters are numbers. If all are digits, we will get one message that the password is with digits and move on with the program. If any of them (or all) is not a digit, then the user should enter password again. (E.g. 465486 is acceptable. hell3429384 or sfdkjsfkj is not acceptable)

Apparently, my code is not working correctly, since whether I give a number or a letter to the password, I get the same result. Am I looping something wrong, or am I using the isDigit method wrong?

import java.util.*; 
public class Password {
    public static void main(String[] args) {
        Scanner passn = new Scanner(System.in);
        System.out.println("Give password: "); 
        String pass = passn.nextLine(); /* user enters password*/
        int length = pass.length();
        boolean isadigit; 
        for(int i = 0; i < length; i++) { /*looping each character one by    one*/     
            char character= pass.charAt(i);
            if (Character.isDigit(i)) { /*checking if each character is digit*/
                isadigit = true; /* if it is, give the value to isadigit true*/
                System.out.println("PASSWORD is w digits");
            }
            else {
                System.out.println("PASSWORD w/out digits");
                passn.nextLine();
            }
        }
    }
}

Answer 1

If you can use java-8 there is one-liner:

pass.chars().allMatch(Character::isDigit)

Answer 2

You are not checking each character, but each index value.

Change

if(Character.isDigit(i))

to

if(Character.isDigit(character))

Also: you don't break out of the loop when you encounter a non-digit...

Answer 3

A side note if you are on Android:

You can use TextUtils.isDigitsOnly() directly, e.g.

TextUtils.isDigitsOnly(myString)

And just in case, an empty string is digit only because it doesn't contain any non-digit; also this method is not null-tolerant.

Answer 4

To be honest: You could write code like you did. But it would be better to use a regular expression on that. You want to know, if a certain String only contains digits. Here is the code:

String foo = "My_pwd_is_wrong_123!";
String bar = "123";
boolean foo_ok = foo.matches("^[0-9]*$") // Will be "false"
boolean bar_ok = bar.matches("^[0-9]*$") // Will be "true"

Answer 5

Ok, in that case: Your Problem is, that you continue your loop after identifiyng a non-digit in one Password. You need to BREAK your loop, as soon as you find a non-digit in the pwd:

public class TEST {

    public static void main(String[] args) {
        Scanner passn = new Scanner(System.in);
        System.out.println("Give password: "); 
        String pass = passn.nextLine(); /* user enters password*/
        int length = pass.length();

        boolean isadigit = true; 

        for(int i = 0; i<length; i++) { /*looping each character one by    one*/     
            char character= pass.charAt(i);
            if (!Character.isDigit(character)) { /*checking if current character is digit*/
                isadigit = false; /* if it is not, give the value to isadigit false*/
                break;
            }
        }

        if(isadigit)
            System.out.println("PASSWORD is w digits");
        else
            System.out.println("PASSWORD w/out digits");
    }

}

Answer 6

Please see this sample implementation

    boolean isDigit = false;

    for (int i = 0; i < length; i++) {     
        char character = pass.charAt(i);

        if (Character.isDigit(character)) {
            isDigit = true;
        } else {
            passn.nextLine();
        }
    }

    if (isDigit) {
        System.out.println("PASSWORD is w digits");
    } else {
        System.out.println("PASSWORD w/out digits");
    }

Answer 7

In Kotlin, you can use

text.all { it.isDigit() } 

Answer 8

try to parse the string to Integer. catch the exception

Scanner passn = new Scanner(System.in);
System.out.println("Give password: "); 
String pass = passn.nextLine(); /* user enters password*/
try
{
    Integer.parseInt(pass);
    System.out.println("Digital password!");
}
catch(NumberFormatException nfe){
    System.out.println("without digit password!");
}