To display next N numbers of prime numbers in java

I want to display next n numbers of prime numbers in java

so what i did is accepting the two inputs from user

he enters one number and then he enters the how many next prime numbers to be printed

but i am not getting any output there is no any error

i have created a isprime() which returns true or false if number is prime or not
and then in main() i created count variable to display howmany numbers to be printed

import java.util.Scanner;
class NprimeNumbers 
{
public static boolean isprime(int num)
{
int count=0;
int i;
for(i=1;i<=num;i++)
{
if(num%i==0)
{
count++;
}
}
if(count==2)
return true;
else
return false;
}
public static void main(String[] args)
{
Scanner sc=new Scanner(System.in);
System.out.println();
System.out.print("Enter the number : ");
int number=sc.nextInt();
System.out.print("How many prime numbers to print : ");
int hmw=sc.nextInt();
System.out.println();
System.out.println("------------------------------OUTPUT------------------------------");
System.out.println();
int count=0;           
if(isprime(number))
{
while(count==hmw)
{
System.out.print(number+",");
}
count++;
number++;
}
}
}

The output should be 13,17,19,23,27

The while loop should be on the outside of the if statement as you want it to run until the next 5 primes have been found. You only want to output the number and increase count if isprime() returns true. The number variable should be increased outside of the if statement since we need the next number regardless if the current one was a prime or not.

So it needs to look more like:

number++; // skip the number they entered
int count=0;                   
while (count < hmw) {
if(isprime(number))
{
System.out.print(number+",");  
count++;                        
}
number++;
}

As mentioned, your isprime() function is really inefficient. A slight fix would be to start at 2 and stop at num-1, returning false as soon as one of the numbers evenly divides into the candidate, as there's no reason to check any more numbers past that point. Only return true after you've determined that no numbers evenly divide into the candidate:

public static boolean isprime(int num)
{
for(int i=2;i<num;i++)
{
if(num%i==0)
{
return false;
}
}
return true;
}

If you go a step further, we can reduce the number of checks by using the square root of the candidate number, as described in the trial division section, as the upper bound of the for loop:

public static boolean isprime(int num)
{
int upperBound = (int)Math.sqrt((double)num);
for(int i=2;i<=upperBound;i++)
{
if(num%i==0)
{
return false;
}
}
return true;
}

You problem is the structure and the condition of your while loop. Your condition is count==hmw. This is saying to execute the while loop only if the number of prime numbers they want to print is 0 (because you manually set count to 0). You need to make it count <= hmw (you could make it count != hmw but <= is better because if count somehow goes past hmw you are safe.

The incrementing of your while loop also has some issues. You increment outside the while loop with:

while(count==hmw)
{
System.out.print(number+",");
}
count++;
number++;

You need to put the increments inside the loop:

while(count!=hmw)
{
System.out.print(number+",");
count++;
number++;
}

Now this should be your output:

Enter the number : 3
How many prime numbers to print: 4

------------------------------OUTPUT------------------------------

3,4,5,6,
Process finished with exit code 0

However, if you want to print prime numbers only after the number is input by the user, you need to put your conditional statement in your while loop:

while(count<=hmw)
{
if(isprime(number)) {
System.out.print(number + ",");
count++;
}
number++;
}

Now your output is perfect and looks like this:

Enter the number : 3
How many prime numbers to print: 4

------------------------------OUTPUT------------------------------

3,5,7,11,13,
Process finished with exit code 0

Hope this Helps!

You can use an iterative for-loop to loop hwm times.

Within the for-loop, use a while-loop to check isprime with number.

As a note, in this case, the while-loop doesn't require any enclosing code block, since we'll increase number within the isprime call.
O'Reilly Media – Java, A Beginner's Guide, 5th Edition – "Loops with no Body".

for (int count = 1; count <= hmw; count++) {
    while (!isprime(++number));
    System.out.print(number+",");
}

Here is the input and output.

Enter the number : 11
How many prime numbers to print : 5
------------------------------OUTPUT------------------------------
13,17,19,23,29,

import java.util.Scanner;
class NprimeNumbers {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.print("Enter the number : ");
int currentNumber = scan.nextInt();
System.out.print("How many prime numbers to print : ");
int n = scan.nextInt();
printNPrimes(currentNumber, n);
scan.close();
}
public static boolean isprime(int num) {
for (int divisor = 2; divisor <= Math.sqrt(num); ++divisor) {
if (num % divisor == 0) {
return false;
}
}
return true;
}
public static void printNPrimes(int currentNumber, int n) {
int nextPrime = currentNumber + 1; // 12
while (n > 0) {
if (isprime(nextPrime)) {
System.out.print(nextPrime + " ");
--n;
++nextPrime;
} else {
++nextPrime;
}
}
System.out.println();
}
}