Java Program to Check Prime Number or not

Java Program to Check Prime Number or not using for loop

This java program is used to find the number is prime number or not.

A number greater than 1 is called a prime number, if it has exactly two factors, namely 1 and the number itself.

import java.util.Scanner;	
import java.lang.*;

public class PrimeNumber {

	public static void main(String args[]) {
	  Scanner in = new Scanner(System.in); 
	  System.out.println("Checks Prime Number or not");
	  System.out.println("---------------------------");
	  System.out.print("Enter Number: ");
	  int number = in.nextInt();
	  boolean isPrime = true;
	  for (int i=2;i<number;i++){
		  if(number % i == 0) {
			  isPrime = false;
		  }
	  }
	  if (isPrime) {
		  System.out.println("Number '"+number+"' is a Prime Number!");
	  } else {
		  System.out.println("Number '"+number+"' is not a Prime Number!"); 
	  }
	}
 }

Output:

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Checks Prime Number or not
---------------------------
Enter Number: 4
Number '4' is not a Prime Number!

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Checks Prime Number or not
---------------------------
Enter Number: 13
Number '13' is a Prime Number!

Java Program to Check Prime Number or not using while loop

import java.util.Scanner;	
import java.lang.*;

public class PrimeNumber {

	public static void main(String args[]) {
	  Scanner in = new Scanner(System.in); 
	  System.out.println("Checks Prime Number or not");
	  System.out.println("---------------------------");
	  System.out.print("Enter Number: ");
	  int number = in.nextInt();
	  boolean isPrime = true;
	  int i=2;
	  while (i<number){
		  if(number % i == 0) {
			  isPrime = false;
		  }
		  i++;
	  }
	  if (isPrime) {
		  System.out.println("Number '"+number+"' is a Prime Number!");
	  } else {
		  System.out.println("Number '"+number+"' is not a Prime Number!"); 
	  }
	}
 }

Output:

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Checks Prime Number or not
---------------------------
Enter Number: 19
Number '19' is a Prime Number!

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Checks Prime Number or not
---------------------------
Enter Number: 21
Number '21' is not a Prime Number!

Java Program to List Prime Numbers till Limit using for loop

This java program is used to display the list of prime numbers till the limit specified as user input.

import java.util.Scanner;	
import java.lang.*;

public class PrimeNumber {

	public static void main(String args[]) {
	  Scanner in = new Scanner(System.in); 
	  System.out.println("Prime Numbers List");
	  System.out.println("---------------------------");
	  System.out.print("Enter Limit: ");
	  int limit = in.nextInt();

	  System.out.println("Prime Numbers:");
	  for(int i = 2;i <= limit;i++)                                                     
	  {                                                                             
		boolean isPrime = true;                                                                
	    for(int j = i-1; j > 1 ; j--)                                                   
	    {                                                                           
	       if(i%j == 0){                                                     
	    	   isPrime = false;
	       }
	    }                                                                           
		  if (isPrime) {
			  System.out.print(i+"\t");
		  }                                                      
	  }   
	}
 }

Output:

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Prime Number List
--------------------
Enter Limit: 20
Prime Numbers:
2	3	5	7	11	13	17	19

Java Program to List Prime Numbers till Limit using while loop

import java.util.Scanner;	
import java.lang.*;

public class PrimeNumber {

	public static void main(String args[]) {
	  Scanner in = new Scanner(System.in); 
	  System.out.println("Prime Numbers List");
	  System.out.println("---------------------------");
	  System.out.print("Enter Limit: ");
	  int limit = in.nextInt();

	  System.out.println("Prime Numbers:");
	  int i = 2;
	  while (i <= limit)                                                     
	  {            
		int j = i-1;
		boolean isPrime = true;                                                                
	    while ( j > 1)                                                   
	    {                                                                           
	       if(i%j == 0){                                                     
	    	   isPrime = false;
	       }
	       j--;
	    }                                                                           
		 if (isPrime) {
			 System.out.print(i+"\t");
		 }  
		  
		 i++;
	  }   
	}
 }

Output:

D:\Java_Programs>javac PrimeNumber.java
D:\Java_Programs>java PrimeNumber 
Prime Number List
--------------------
Enter Limit: 25
Prime Numbers:
2	3	5	7	11	13	17	19	23

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