java program to display prime numbers from 1 to 100

1public class Main {
2  public static void main(String[] args) {
3    for (int i = 2; i < 100; ++i) {
4      boolean isPrime = true;
5      int sqrt = (int)Math.ceil(Math.sqrt(i));
6      for (int divisor = 2; divisor <= sqrt; ++divisor) {
7        if (i % divisor == 0) {
8          isPrime = false;
9          break;
10        }
11      }
12      if (isPrime) {
13        System.out.println(i);
14      }
15    }
16  }
17}

1class PrimeNumbers
2{
3   public static void main (String[] args)
4   {		
5       int i =0;
6       int num =0;
7       //Empty String
8       String  primeNumbers = "";
9
10       for (i = 1; i <= 100; i++)         
11       { 		  	  
12          int counter=0; 	  
13          for(num =i; num>=1; num--)
14	  {
15             if(i%num==0)
16	     {
17 		counter = counter + 1;
18	     }
19	  }
20	  if (counter ==2)
21	  {
22	     //Appended the Prime number to the String
23	     primeNumbers = primeNumbers + i + " ";
24	  }	
25       }	
26       System.out.println("Prime numbers from 1 to 100 are :");
27       System.out.println(primeNumbers);
28   }
29}

1public class PrimeNumbersFrom1To100
2{
3   public static void main(String[] args)
4   {
5      int maxNumber = 100;
6      boolean prime = true;
7      String primeNumbers = "";
8      for(int a = 1; a <= maxNumber; a++)
9      {
10         prime = checkPrime(a);
11         if(prime)
12         {
13            primeNumbers = primeNumbers + a + " ";
14         }
15      }
16      System.out.println("Display prime numbers from 1 to " + maxNumber + ": ");
17      System.out.println(primeNumbers);
18   }
19   public static boolean checkPrime(int number)
20   {
21      int remainder;
22      for(int a = 2; a <= number / 2; a++)
23      {
24         remainder = number % a;
25         // if remainder is equal to 0 then number is not prime
26         if(remainder == 0)
27         {
28            return false;
29         }
30      }
31      return true;
32   }
33}