Java Program to Display Factors of a Number

In this article, we will understand how to display the factors of a number. Factors are numbers that divide the original number without leaving a remainder.

For example, 1, 2, 3, 4, 6, and 12 are factors of 12. If a and b are factors of a number, then a x b is also a factor of the number.

If we multiply 3 and 5, we get 15. We say that 3 and 5 are factors of 15. The largest factor of any number is the number itself, and the smallest factor is 1.

• 1 is a factor of every number.
• So, for example, the largest and smallest factors of 12 are 12 and 1.

Below is a demonstration of the same -

Input: 45
Output: The factors of 45 are: 1 3 5 9 15 45

Finding Factors of a Number using Java

There are the following are various ways to find the factors of a number -

• Using a for loop

• Using a while loop

• Using a do-while loop

• Using the square root

Using a for loop

A for loop is used to repeat a set of statements multiple times. To find the factorial using a for loop. We need to follow the steps given below -

1. START 
2. Declare two integer values, namely my_input and i. 
3. Read the required values from the user/ define the values. 
4. Using a for loop, iterate from 1 to my_input, check if the modulus my_input value and 'i' value leaves a reminder. If no reminder is shown, then it's a factor. Store the value.
5. Display the result. 
6. Stop
   

Example 1

Here, the integer has been previously defined, and its value is accessed and displayed on the console -

import java.util.Scanner;
public class Factors {
   public static void main(String[] args) {
      int my_input, i;
      my_input = 45;
      System.out.println("The number is defined as " +my_input);
      System.out.print("The factors of " + my_input + " are: ");
      for (i = 1; i <= my_input; ++i) {
         if (my_input % i == 0) {
            System.out.print(i + " ");
         }
      }
   }
}

Output

The number is defined as 45
The factors of 45 are: 1 3 5 9 15 45

Example 2

Here is an example where we accept values from the user -

import java.util.Scanner;
public class Factors {
   public static void main(String[] args) {
      int my_input, i;
      System.out.println("Required packages have been imported");
      Scanner my_scanner = new Scanner(System.in);
      System.out.println("A reader object has been defined ");
      System.out.print("Enter the number : ");
      my_input = my_scanner.nextInt();
      System.out.print("The factors of " + my_input + " are: ");
      for (i = 1; i <= my_input; ++i) {
         if (my_input % i == 0) {
            System.out.print(i + " ");
         }
      }
   }
}

Output

Required packages have been imported
A reader object has been defined
Enter the number : 45
The factors of 45 are: 1 3 5 9 15 45

Using a while loop

Let's see the following steps to find factors of a number using a while loop -

1. Declare and initialize a number whose factors you want.
2. Initialize a counter variable (e.g., i = 1) to start iterating from 1.
3. Use a while loop that will iterate till (i <= number)i is less than or equal to the number.
4. Inside the loop, check if the number is divisible by i (i.e., number % i == 0). 
5. If true, i is a factor and increment the counter after each iteration to check the next number.
6. Repeat until all numbers are checked.

Example

In the following example, we are calculating the factorial of a number using the while loop -

public class FactorFind {
   public static void main(String[] args) {
      int number = 20; // Define the number
      int i = 1;
      System.out.println("Factors of " + number + " are:");
      while (i <= number) {
         if (number % i == 0) {
            System.out.print(i + " ");
         }
         i++; //increment value
      }
   }
}

This will produce the following output -

Factors of 20 are:
1 2 4 5 10 20 

Using a do-while loop

Let's see the following steps to find factors of a number using a do-while loop -

1. Declare and initialize a number whose factors you want.
2. Initialize a counter variable (e.g., i = 1) to start iterating from 1.
3. Use a do-while loop till (i <= number) and check if the number is divisible by i (i.e., number % i == 0).
4. If yes, then i is a factor and increment the counter variable after each iteration.
   

Example

Here we are calculating the factorial of a number using the do-while loop -

public class FactorFind {
   public static void main(String[] args) {
      int number = 30; // Define the number
      int i = 1;
      System.out.println("Factors of " + number + " are:");
      do {
         if (number % i == 0) {
            System.out.print(i + " ");
         }
         i++;
      } while (i <= number);
   }
}

Following is the output of the above program -

Factors of 30 are:
1 2 3 5 6 10 15 30 

Using the Math.sqrt() Method

Every number has factors that are in pairs; for example, 2 and 50 are both factors of 100 because 2 × 50 = 100.

To find all the factors, we can check up to only the square root of the number. It is an optimized solution to find the factors of a number. If a pair has the same number twice (like 10 × 10), we only count it once. Let's see the following steps to find factors of a number using a for loop -

1. Declare and initialize the number n whose factors you want.
2. Use Loop and iterate from 1 to the square root of n only (i.e., i goes from 1 to ?n).
3. Check divisibility, if n % i == 0.
4. If divisible and if i and n/i are equal (meaning n is a perfect square), print i only once.
5. Else, print both i and its corresponding factor n/i.
   

Example

In the following example, we are calculating the factorial of a number using the sqrt() method -

public class FactorFind {
   public static void main(String[] args) {
      // Store the number whose factors are to be found
      int n = 60;
      System.out.print("Factors of " + n + " are:");
      // Loop from 1 to square root of n
      for (int i = 1; i <= Math.sqrt(n); i++) {
         // Check if i is a factor
         if (n % i == 0) {
            // If divisors are equal (perfect square), print once
            if (n / i == i) {
               System.out.print(" " + i);
            } else {
               // Print both factors
               System.out.print(" " + i + " " + (n / i));
            }
         }
      }
   }
}

Following is the output of the above program -

Factors of 60 are: 1 60 2 30 3 20 4 15 5 12 6 10