Print prime numbers from 1 to 100 in Java

In this post, you will learn different ways to print prime numbers from 1 to 100 using the Java programming language.

A prime number is a whole number greater than 1 whose only factors are 1 and itself, like -2, 3, 5, 7, 11, etc. For example, 17 is a prime number because it is only divisible by 1 and 17. On the other hand, 18 is not a prime number because it is divisible by 2, 3, 6, 9, and the number itself.

Java print prime numbers from 1 to 100 using for loop

Here, we have used for loop to get prime numbers from 1 to 100. We loop over the number range (1 to 100) and check whether the number is prime or not. The for loop iterates from i = 0 to i = given number. If the remainder of i/num = 0, then it increases the count by 1. After all the iterations, if counter=2, then that number is a prime number.

public class CheckPrimeNumbers
{
    public static void main (String[] args)
    {		
       int i =0;
       int num =0;
       
       String  prime_numbers = "";

       for (i = 1; i <= 100; i++)         
       { 		  	  
          int counter=0; 	  
          for(num =i; num>=1; num--)
    	  {
             if(i%num==0)
    	     {
     		    counter = counter + 1;
    	     }
    	  }
    	  if (counter ==2)
    	  {
    	     prime_numbers = prime_numbers + i + " ";
    	  }	
       }	
       System.out.println("Prime Numbers between 1 and 100 :");
       System.out.println(prime_numbers);
    }
}

Prime Numbers between 1 and 100 :
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 

Java print prime numbers from 1 to 100 using while loop

Here, we have used the while loop to get prime numbers from 1 to 100.

public class PrimeNumbers  
{  
    public static void main(String[] args)   
    {  
    int counter=0, n=0, i=1, j=1;  
    while(i<100)  
    {  
        j=1;  
        counter=0;  
        while(j<=i)  
        {  
            if(i%j==0)  
            counter++;  
            j++;   
        }  
        if(counter==2)  
        {  
            System.out.printf("%d ",i);  
            n++;  
        }  
        i++;  
    }    
    }  
} 

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 

In the above code, we have two while loops. The inner while loop does the testing with each possible divisor. If the inner loop finds a divisor, the number is not prime, so it breaks out without printing anything. If counter = 2, then we can assume that the number is prime. The outer loop works through all the numbers between 1 and 100. This loop is broken when we have reached the breaking point of numbers to test.

Java print prime numbers from 1 to 100 using method

Here, we ask the user to provide the minimum and maximum values, and we separate the logic of the prime numbers and place it in a separate method.

import java.util.Scanner;

public class PrimeNumbers {
	private static Scanner sc;
	public static void main(String[] args) 
	{
		int num, min, max, i, count; 
		sc = new Scanner(System.in);
		
		System.out.print("Please enter the minimum value: ");
		min = sc.nextInt();	
		
		System.out.print("Please enter the maximum value: ");
		max = sc.nextInt();	
	
		System.out.println("Prime numbers from 1 to 100 are: ");	
		for(num = min; num <= max; num++)
		{
			count = 0;
		    for (i = 2; i <= num/2; i++)
		    {
		    	if(num % i == 0)
		    	{
		    		count++;
		    		break;
		    	}
		    }
		    if(count == 0 && num != 1 )
		    {
		    	System.out.print(num + " ");
		    }  
		}
	}
}

Please enter the minimum value: 1
Please enter the maximum value: 100
Prime numbers from 1 to 100 are: 
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

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