Java program to find the factors of a number

Java program to find the factors of a number:

In this post, we will learn how to find the factors of a number in Java. A number is called factor of a different number, if it can divide the number completely i.e. if the remainder is 0.

For example, 1, 2, 4 are factors of 4.

To solve this program programmatically, we can use a loop that will check all numbers from 1 to that number.

We can use any loop. In this post, I will show you how to do that using a for loop, while loop, do while loop and also by using a separate function.

Method 1: Find all factors of a number using a for loop in Java:

Let’s take a look at the below program:

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number : ");

        int no = sc.nextInt();
        List<Integer> factorsList = new ArrayList<>();

        System.out.println("Factors are : ");

        for (int i = 1; i <= no; i++) {
            if (no % i == 0) {
                factorsList.add(i);
            }
        }

        System.out.println(factorsList);
    }
}

Explanation:

Here,

We are asking the user to enter a number and storing that value in the no variable.
factorsList is an ArrayList that can hold integers. This is used to store the factors.
Using a for loop, we are iterating from i = 1 to i = no and for each value of i, we are checking if it can perfectly divide no or not.
If yes, we are adding that to the list factorsList.
Once the for loop ends, we are printing the factorsList which holds all factors of no.

Sample output:

It will print output as like below:

Enter a number : 
6
Factors are : 
[1, 2, 3, 6]

Enter a number : 
7
Factors are : 
[1, 7]

Method 2: Find all factors of a number using a while loop in Java:

Let’s write the same program using while.

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number : ");

        int no = sc.nextInt();
        List<Integer> factorsList = new ArrayList<>();

        System.out.println("Factors are : ");

        int i = 1;

        while(i <= no) {
            if (no % i == 0) {
                factorsList.add(i);
            }
            i++;
        }

        System.out.println(factorsList);
    }
}

Here,

we are using a while loop that replaces for loop.
In this loop, the while loop runs from i = 1 to i = no. For each iteration, we are incrementing the value of i by 1. Also, similar to the above program, we are adding the value of i to factorsList if i is a factor of no.
Finally we are printing the value of factorsList.

Method 3: Find all factors of a number using a do-while loop in Java:

We can also use a do-while loop to find the factors. For example:

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number : ");

        int no = sc.nextInt();
        List<Integer> factorsList = new ArrayList<>();

        System.out.println("Factors are : ");

        int i = 1;

        do {
            if (no % i == 0) {
                factorsList.add(i);
            }
            i++;
        }while(i <= no);

        System.out.println(factorsList);
    }
}

It will print the same output.

Method 4: Find all factors of a number using a different function:

We can also use a different function and put the part to calculate the factors in that function. Using a function has many advantages like we can remove reusable code and put it in a function.

For example, the below program uses the findFactors function to get the list of factors. I am using do-while, but you can use any other loop if you want. It returns a list of integers holding the factors.

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
    private static List<Integer> findFactors(int no) {
        List<Integer> factorsList = new ArrayList<>();
        int i = 1;
        do {
            if (no % i == 0) {
                factorsList.add(i);
            }
            i++;
        } while (i <= no);
        return factorsList;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.println("Enter a number : ");
        int no = sc.nextInt();

        System.out.println("Factors are : ");
        System.out.println(findFactors(no));
    }
}

findFactors is a private function, but we can make it public and call it from different parts of the program.

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Java program to find the factors of a number