General Structure of a Java Program

//Document section – we write a description of the program
//Package statement – we add packages here
//Interface statement – we declare interface here
class Test     // class definition
{
   public static void main(String args[])    // main function definition
   {
       // program code
   }
 }

Example : Sum of two numbers
 class AddTwoNumbers
{
   public static void main(String[] args)
 {
      int num1 = 5, num2 = 15, sum;
      sum = num1 + num2;
      System.out.println("Sum of two numbers: "+sum);
   }
}

Output:
Sum of these numbers: 20

Example: Sum of two numbers using Command line arguments
class AddTwoNumbers
{
   public static void main(String[] args)
  {
        int num1, num2, sum;
        num1 = Integer.parseInt(args[0]);
        num2 = Integer.parseInt(args[1]);
        sum = num1 + num2;
        System.out.println("Sum of two numbers: "+sum);
    }
}
Output:
Enter First Number: 
12
Enter Second Number: 
19
Sum of these numbers: 31

Example: Sum of two numbers using Scanner
import java.util.Scanner;
class AddTwoNumbers
{
   public static void main(String[] args)
  {
        int num1, num2, sum;
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter First Number: ");
        num1 = sc.nextInt();
        System.out.println("Enter Second Number: ");
        num2 = sc.nextInt();
        sum = num1 + num2;
        System.out.println("Sum of two numbers: "+sum);
    }
}
Output:
Enter First Number: 
121
Enter Second Number: 
19
Sum of these numbers: 140

Example 1: convert temperature given in foreign heat to celsius
Solution:
import java.util.Scanner;
class FahrenheitToCelsius
{
  public static void main(String[] args)
 {
    float temperature;
    Scanner in = new Scanner(System.in);
    System.out.println("Enter temperature in Fahrenheit");
    temperature = in.nextInt();
    temperature = ((temperature - 32)*5)/9;
    System.out.println("Temperature in Celsius = " + temperature);
  }
}
Output:
H:\>java FahrenheitToCelsius
Enter temperature in Fahrenheit
98
Temperature in Celsius = 36.666668

Example 2. program to calculate Area Of Rectangle.
Solution:
import java.util.Scanner;
class AreaOfRectangle
{
   public static void main (String[] args)
   {
   Scanner scanner = new Scanner(System.in);
   System.out.println("Enter the length of Rectangle:");
   double length = scanner.nextDouble();
   System.out.println("Enter the width of Rectangle:");
   double width = scanner.nextDouble();
   //Area = length*width;
   double area = length*width;
   System.out.println("Area of Rectangle is:"+area);
   }}
Output:
Enter the length of Rectangle:
2
Enter the width of Rectangle:
8
Area of Rectangle is:16.0

Example 3:Program to calculate compound interest
Solution:
import java.util.Scanner;
class CompoundInterest
{
    public static void main(String args[])
   {
        Scanner s=new Scanner(System.in);
        System.out.println("Enter Principal :");
        double p=s.nextInt();
        System.out.println("Enter Rate of Interest:");
        double r=s.nextInt();
        System.out.println("Enter Time Period:");
        double n=s.nextInt();
        double ci=p *( Math.pow(1+0.01*r,n)-1);
        double amt=p+ci;
        System.out.println("Compound Interest after " + n + " years: "+ci);
        System.out.println("Amount after " + n + " years: "+amt);
    }  
  }
Output:
H:\>java CompoundInterest
Enter Principal :
25000
Enter Rate of Interest:
4
Enter Time Period:
5
Compound Interest after 5.0 years: 5416.322560000003
Amount after 5.0 years: 30416.322560000004