Write a program to find first n prime numbers in Java

In this tutorial, we will discuss the concept of an Example program – write a program to find first n prime numbers in Java.

In this post, we are going to learn how to write a program to find the first n prime number using for, while, and do-while loops in Java programming language:

The number that can be divided by 1 and itself only. it is called the prime number

for Example 2,3,5,7,11,13,….

To understand this example program, you should have previous knowledge of the following Java topics

for loop in Java language

while loop in Java language

do-while loop in Java language

if statement in Java language

Example program to print first n prime numbers

Print the first n prime number using the for loop

In this program, we will print the first “n” prime numbers, using for loop. first, the user is asked to enter a number randomly for n, and then the program prints the prime numbers 1 to n.

Program 1

//print the prime number in given range(0 - n)
import java.util.*;
public class PrimeNum_firstN1{
public static void main(String args[]){
    Scanner sc=new Scanner(System.in);
    //scanner class for input
int num=1,y=3,count,j;
//variable declaration and initialization
System.out.println("Please Enter the number for range(0 - n): ");
int n=sc.nextInt();
if(n>=1){
    System.out.println("The first "+n+" prime numbers are: " );
    System.out.println(2);
}
for(count=2; count<=n;){
    for(j=2; j<=Math.sqrt(y); j++){
        if(y%j==0){
            num=0;
            break;
        }
    }
    if(num!=0){
        System.out.println(y);
        count++;
    }
    num=1;
    y++;
}
}
}

When the above code is executed, it produces the following result

Please Enter the number for range(0 - n):

10

The first 10 prime numbers are:

2
3
5
7
11
13
17
19
23
29

Print the first n prime number using the while loop

In this program, we will print the first “n” prime numbers, using a while loop. first, the user is asked to enter a number randomly for n, and then the program prints the prime numbers 1 to n.

Program 2

//print first n prime numbers using while
import java.util.*;
public class Prime_firstNwhile{
public static void main(String args[]){
    Scanner sc=new Scanner(System.in);
    //scanner class for input
int n,num=1,y=3,count,j;
System.out.println("Please Enter the number for print prime: ");
n=sc.nextInt();
if(n>=1){
    System.out.println("First "+n+" prime numbers are: " );
    System.out.println(2);
}
count=2;
while(count<=n){
    j=2; 
    while(j<=Math.sqrt(y)){
        if(y%j==0){
            num=0;
            break;
        }
         j++;
    }
    if(num!=0){
        System.out.println(y);
        count++;
    }
    num=1;
    y++;
}
}
}

When the above code is executed, it produces the following result

Please Enter the number for range(0 - n):

5

The first 5 prime numbers are:
2
3
5
7
11

Print the first n prime number using the do-while loop

In this program, we will print the first “n” prime numbers, using a do-while loop. first, the user is asked to enter a number randomly for n, and then the program prints the prime numbers 1 to n.

Program 2

//Print first n prime numbers using do-while
import java.util.*;
public class Prime_FirstNDowhile2{
public static void main(String args[]){
    Scanner sc=new Scanner(System.in);
    //scanner class for input
int n,num=1,y=3,count,j;
System.out.println("Please Enter the number for print prime: ");
n=sc.nextInt();
if(n>=1){
    System.out.println("The First "+n+" prime numbers are: " );
    //display first n priume number
    System.out.println(2);
}
count=2;
do{//outer do-while
    j=2; 
    do{//inner do-while
        if(y%j==0){
            num=0;
            break;
        }
         j++;
    }while(j<=Math.sqrt(y));
    if(num!=0){
        System.out.println(y);
        count++;
    }
    num=1;
    y++;
}while(count<=n);
}
}

When the above code is executed, it produces the following result

Please Enter the number for print prime:

7

The first 5 prime numbers are:

2
3
5
7
11
13
17

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