Java Program to Count Number of Digits in a String

Last Updated : 02 Nov, 2022

The string is a sequence of characters. In java, objects of String are immutable. Immutable means that once an object is created, it's content can't change. Complete traversal in the string is required to find the total number of digits in a string.

Examples:

Input : string = "GeeksforGeeks password is : 1234"
Output: Total number of Digits = 4

Input : string = "G e e k s f o r G e e k 1234"
Output: Total number of Digits = 4

Approach:

Create one integer variable and initialize it with 0.
Start string traversal.
If the ASCII code of character at the current index is greater than or equals to 48 and less than or equals to 57 then increment the variable.
After the end of the traversal, print variable.

Below is the implementation of the above approach:

Java

// Java Program to Count Number of Digits in a String
public class GFG {

    public static void main(String[] args)
    {
        String str = "GeeksforGeeks password is : 1234";
        int digits = 0;
        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) >= 48 && str.charAt(i) <= 57)
                digits++;
        }
        System.out.println("Total number of Digits = "
                           + digits);
    }
}

Output

Total number of Digits = 4

Time Complexity: O(N), where N is the length of the string.

Approach : Using isDigit() method

Java

// Java Program to Count Number of Digits in a String
public class GFG {

    public static void main(String[] args)
    {
        String str = "GeeksforGeeks password is : 1234";
      
        int digits = 0;
        for (int i = 0; i < str.length(); i++) {
            if (Character.isDigit(str.charAt(i)))
                digits++;
        }
        System.out.println("Total number of Digits = "
                           + digits);
    }
}

Output

Total number of Digits = 4

Approach : Using contains() method and ArrayList

Java

// Java Program to Count Number of Digits in a String
import java.lang.*;
import java.util.*;
public class Main{

    public static void main(String[] args)
    {
        String str = "GeeksforGeeks password is : 1234";
        String num="0123456789";
        ArrayList<Character> numbers= new ArrayList<>();
        for(int i=0;i<num.length();i++)
        {
            numbers.add(num.charAt(i));
        }
        int digits = 0;
        for (int i = 0; i < str.length(); i++) {
            if (numbers.contains(str.charAt(i)))
                digits++;
        }
        System.out.println("Total number of Digits = "+ digits);
    }
}