Program to display all prime number below a user entered number

Create a new Class with name Disp_primes:

import java.util.Scanner;

public class Disp_primes {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
       
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number : ");
        int num = sc.nextInt();
        System.out.println("prime numbers below "+num+" are :");
        int rem=0;
        if(num==2){
            System.out.print(num+" is even prime");
        }
        else{
            for(int i=num;i>2;i--){
                int count=2;
        while(count<i){
            rem = i%count;
            if(rem==0)
                break;
            else
                count++;
                    }
        if(rem!=0)
            System.out.print(i+",");
        }
            if(num>2){
                System.out.print("2");
            }
        }
    }

}

Output:(Click on image to enlarge):

(Comment if you have any doubts)
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Program to check if a number is Prime or not

Create a new Class with name Chk_prime :

import java.util.Scanner;
 
public class Chk_prime {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int rem=0,i=2;
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number to check if it is prime : ");
        int num = sc.nextInt();
        System.out.println("You entered : "+num);
        if(num==2){
            System.out.print(num+" is even prime");
        }
        else{
        while(i<num){
            rem = num%i;
            if(rem==0){
                System.out.print(num+" is not prime");
            break;}
            else
                i++;
                    }
        if(rem!=0)
            System.out.print(num+" is prime");
        }
        }
    }

Output:(Click on image to enlarge)

(Comment if you have any doubts)

Program to check if a year is leap year or not

Create a new class with name Chk_leapyear: 

import java.util.Scanner;

public class Chk_leapyear {
   
    public static void main(String[] args) {
        // TODO Auto-generated method stub
       
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a year to check if it is leap year : ");
        int year = sc.nextInt();
        System.out.println("You entered : "+year);
        if(year%100==0){
            if(year%400==0)
                System.out.println(year+" is a leap year");
            else
                System.out.println(year+" is not a leap year");
        }
        else{
            if(year%4==0)
                System.out.println(year+" is a leap year");
            else
                System.out.println(year+" is not a leap year");
        }
    }

}

Output:(Click on image to enlarge)

Enter the year you want to check in the output window as shown above.
(Comment if you have any doubts)

First Java program

A demo file to initialize and display different variables:

• Create a new class with name VariablesDemo:

public class VariablesDemo {

    public static void main(String[] args) {
   
        /* Declaration of variables  */
         int Id;
         String name;
         char gender;
         double salary;
    
         /* Initialization of variables*/
         Id = 4348;
         name = "Employer";
         gender ='M';
         salary = 25000.0;
    
        /* Display the employee details */
         System.out.println("Id : "+ Id);
         System.out.println("Name : "+ name);
         System.out.println("Gender : "+ gender);
         System.out.println("Salary : "+ salary);

        }
}

NOTE: 

• The text between "/* " and "*/" will not be executed.They are used to write comments.
• For single line comments use "//" 

 Output:(Click on the image to enlarge)

Demonstration of Continue statement

Create a new class with name ControlContinue:

class ControlContinue {
    public static void main(String args[]) {
        //boolean bool = true;
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 10; j++) {
                System.out.print(j + "\t");
                if (j > 5) {
                    System.out.println();
                    continue;
                }
            }
            System.out.println("Outer Loop");
        }
        System.out.println("End");
    }
}

Output:(Click on the image to enlarge)

Demonstration of break statement

create a class with name Control:

class Control {
    public static void main(String args[]) {
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < 10; j++) {
                System.out.print(j + "\t");
                if (j > 5) {
                    break;
                }
            }
            System.out.println("Outer Loop :"+(i+1));
        }
        System.out.println("End");
    }
}

Output: (Click on the image to enlarge)

Program to print Fibonacci numbers below 'n'

Create a new Class with name Fibonacci:

import java.io.*;
class Fibonacci {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("enter the value n");
        int n = Integer.parseInt(br.readLine());
        int a = 0, b = 1, c = 0;
        if (n > 0) {
            System.out.println("---------------------");
            System.out.println("\t" + a);
            System.out.println("\t" + b);
            do {
                c = a + b;
                if(c<=n)
                System.out.println("\t" + c);
                a = b;
                b = c;
            } while (c <= n);
            System.out.println("---------------------");
        } else {
            System.out.println("enter positive n value");
        }
    }
}

Output:(Click on image to enlarge):

Comment if you have any doubts.