Java Examples

Java Program - Count digits in an Integer



In Java, count of digits in a given integer can be found out by using below mentioned methods.

Method 1: Using iteration

The method involves the following steps:

Input: MyNum
Step 1: Initialize the count = 0
Step 2: Iterate over MyNum while it is not zero.
   Step 2a: Update MyNum by MuNum / 10
   Step 2b: Increase count by 1
Step 3: Return count

Example:

Input: 564
count: 0

Iteration 1: 
    MyNum: 564 / 10 = 56
    count: 0 + 1 = 1

Iteration 2: 
    MyNum: 56 / 10 = 5
    count: 1 + 1 = 2

Iteration 3: 
    MyNum: 5 / 10 = 0
    count: 2 + 1 = 3

return count = 3

The below block of code shows the implementation of above concept:

public class MyClass {
  //method to count number of digits
  static int countDigits(long MyNum) {    
    int count = 0;

    while(MyNum != 0){
      MyNum = MyNum / 10;
      count++;
    }
    return count;
  }  

  public static void main(String[] args) {
    long x = 123;
    long y = 459709;
    System.out.println(x + " contains: " + countDigits(x) + " digits");
    System.out.println(y + " contains: " + countDigits(y) + " digits");
  }
}

The above code will give the following output:

123 contains: 3 digits
459709 contains: 6 digits

Method 2: Using Recursion

The above result can also be achieved using recursive method. Consider the example below:

public class MyClass {
  //method to count number of digits
  static int countDigits(long MyNum) {    
    if(MyNum != 0)
      return 1 + countDigits(MyNum/10);
    else
      return 0;
  }  

  public static void main(String[] args) {
    long x = 564;
    long y = 980620;
    System.out.println(x + " contains: " + countDigits(x) + " digits");
    System.out.println(y + " contains: " + countDigits(y) + " digits");
  }
}

The above code will give the following output:

564 contains: 3 digits
980620 contains: 6 digits

Method 3: Using log method

The log (base-10) of absolute value of a given number can be used to find out the number of digits in a given number. Consider the example below:

public class MyClass {
  //method to count number of digits
  static int countDigits(long MyNum) {    
    return  (int)Math.log10(Math.abs(MyNum)) + 1;
  }  

  public static void main(String[] args) {
    long x = 564;
    long y = -12345;
    long z = 980620;
    System.out.println(x + " contains: " + countDigits(x) + " digits");
    System.out.println(y + " contains: " + countDigits(y) + " digits");
    System.out.println(z + " contains: " + countDigits(z) + " digits");
  }
}

The above code will give the following output:

564 contains: 3 digits
-12345 contains: 5 digits
980620 contains: 6 digits

Method 4: Using length of string

This can also be achieved by converting the absolute value of number into a string and then finding out the length of the string to get the number of digits in the original number. Consider the example below:

public class MyClass {
  //method to count number of digits
  static int countDigits(long MyNum) {    
    String MyStr = Long.toString(MyNum);
    return  MyStr.length();
  }  

  public static void main(String[] args) {
    long x = 564;
    long y = -12345;
    long z = 980620;
    System.out.println(x + " contains: " + countDigits(x) + " digits");
    System.out.println(y + " contains: " + countDigits(y) + " digits");
    System.out.println(z + " contains: " + countDigits(z) + " digits");
  }
}

The above code will give the following output:

564 contains: 3 digits
-12345 contains: 5 digits
980620 contains: 6 digits




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