Java Basic Examples

 Hello World example
/*
Java Hello World example.
*/

public class HelloWorldExample{

  public static void main(String args[]){

    /*
    Use System.out.println() to print on console.
    */
    System.out.println("Hello World !");

  }

}

/*

OUTPUT of the above given Java Hello World Example would be :

Hello World !

*/
Java Class example
/*
Java Class example.
This Java class example describes how class is defined and being used
in Java language.

Syntax of defining java class is,
<modifier> class <class-name>{
  // members and methods
}
*/

public class JavaClassExample{
  /*
  Syntax of defining memebers of the java class is,
    <modifier> type <name>;
  */
  private String name;
  /*
  Syntax of defining methods of the java class is,
  <modifier> <return-type> methodName(<optional-parameter-list>) <exception-list>{
                    ...
  }
  */
  public void setName(String n){
    //set passed parameter as name
    name = n;
  }
  public String getName(){
    //return the set name
    return name;
  }
  //main method will be called first when program is executed
  public static void main(String args[]){
    /*
    Syntax of java object creation is,
    <class-name> object-name = new <class-constructor>;
    */
    JavaClassExample javaClassExample = new JavaClassExample();
    //set name member of this object
    javaClassExample.setName("Visitor");
    // print the name
    System.out.println("Hello " + javaClassExample.getName());      
  }
}
 
/*
OUTPUT of the above given Java Class Example would be :
Hello Visitor
*/

Calculate Circle Area using Java Example
/*
    Calculate Circle Area using Java Example
    This Calculate Circle Area using Java Example shows how to calculate
    area of circle using it's radius.
*/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateCircleAreaExample {

    public static void main(String[] args) {

        int radius = 0;
        System.out.println("Please enter radius of a circle");

        try
        {
            //get the radius from console
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            radius = Integer.parseInt(br.readLine());
        }
        //if invalid value was entered
        catch(NumberFormatException ne)
        {
            System.out.println("Invalid radius value" + ne);
            System.exit(0);
        }
        catch(IOException ioe)
        {
            System.out.println("IO Error :" + ioe);
            System.exit(0);
        }
 
        /*
         * Area of a circle is
         * pi * r * r
         * where r is a radius of a circle.
         */

        //NOTE : use Math.PI constant to get value of pi
        double area = Math.PI * radius * radius;

        System.out.println("Area of a circle is " + area);
    }
}

/*
Output of Calculate Circle Area using Java Example would be
Please enter radius of a circle
19
Area of a circle is 1134.1149479459152

Calculate Circle Perimeter using Java Example
/*
    Calculate Circle Perimeter using Java Example
    This Calculate Circle Perimeter using Java Example shows how to calculate
    Perimeter of circle using it's radius.
*/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateCirclePerimeterExample {

    public static void main(String[] args) {

        int radius = 0;
        System.out.println("Please enter radius of a circle");

        try
        {
            //get the radius from console
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            radius = Integer.parseInt(br.readLine());
        }
        //if invalid value was entered
        catch(NumberFormatException ne)
        {
            System.out.println("Invalid radius value" + ne);
            System.exit(0);
        }
        catch(IOException ioe)
        {
            System.out.println("IO Error :" + ioe);
            System.exit(0);
        }
 
        /*
         * Perimeter of a circle is
         * 2 * pi * r
         * where r is a radius of a circle.
         */

        //NOTE : use Math.PI constant to get value of pi
        double perimeter = 2 * Math.PI * radius;

        System.out.println("Perimeter of a circle is " + perimeter);
    }
}
 
/*
Output of Calculate Circle Perimeter using Java Example would be
Please enter radius of a circle
19
Perimeter of a circle is 119.38052083641213
*/
Calculate Rectangle Area using Java Example
/*
    Calculate Rectangle Area using Java Example
    This Calculate Rectangle Area using Java Example shows how to calculate
    area of Rectangle using it's length and width.
*/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateRectArea {

    public static void main(String[] args) {

        int width = 0;
        int length = 0;

        try
        {
            //read the length from console
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

            System.out.println("Please enter length of a rectangle");
            length = Integer.parseInt(br.readLine());

            //read the width from console
            System.out.println("Please enter width of a rectangle");
            width = Integer.parseInt(br.readLine());


        }
        //if invalid value was entered
        catch(NumberFormatException ne)
        {
            System.out.println("Invalid value" + ne);
            System.exit(0);
        }
        catch(IOException ioe)
        {
            System.out.println("IO Error :" + ioe);
            System.exit(0);
        }

        /*
         * Area of a rectangle is
         * length * width
        */

        int area = length * width;

        System.out.println("Area of a rectangle is " + area);
    }

}

/*
Output of Calculate Rectangle Area using Java Example would be
Please enter length of a rectangle
10
Please enter width of a rectangle
15
Area of a rectangle is 150
*/
 
Calculate Rectangle Perimeter using Java Example
/*
    Calculate Rectangle Perimeter using Java Example
    This Calculate Rectangle Perimeter using Java Example shows how to calculate
    perimeter of Rectangle using it's length and width.
*/
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateRectPerimeter {

    public static void main(String[] args) {

        int width = 0;
        int length = 0;

        try
        {
            //read the length from console
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

            System.out.println("Please enter length of a rectangle");
            length = Integer.parseInt(br.readLine());

            //read the width from console
            System.out.println("Please enter width of a rectangle");
            width = Integer.parseInt(br.readLine());


        }
        //if invalid value was entered
        catch(NumberFormatException ne)
        {
            System.out.println("Invalid value" + ne);
            System.exit(0);
        }
        catch(IOException ioe)
        {
            System.out.println("IO Error :" + ioe);
            System.exit(0);
        }

        /*
         * Perimeter of a rectangle is
         * 2 * (length + width)
        */

        int perimeter = 2 * (length + width);

        System.out.println("Perimeter of a rectangle is " + perimeter);
    }

}

/*
Output of Calculate Rectangle Perimeter using Java Example would be
Please enter length of a rectangle
10
Please enter width of a rectangle
15
Perimeter of a rectangle is 50
*/

Even Odd Number Example
/*
  Even Odd Number Example
  This Java Even Odd Number Example shows how to check if the given
  number is even or odd.
*/

public class FindEvenOrOddNumber {

    public static void main(String[] args) {

        //create an array of 10 numbers
        int[] numbers = new int[]{1,2,3,4,5,6,7,8,9,10};

        for(int i=0; i < numbers.length; i++){

            /*
             * use modulus operator to check if the number is even or odd.   
             * If we divide any number by 2 and reminder is 0 then the number is
             * even, otherwise it is odd.
             */

             if(numbers[i]%2 == 0)
                 System.out.println(numbers[i] + " is even number.");
             else
                 System.out.println(numbers[i] + " is odd number.");

        }

    }
}

/*
Output of the program would be
1 is odd number.
2 is even number.
3 is odd number.
4 is even number.
5 is odd number.
6 is even number.
7 is odd number.
8 is even number.
9 is odd number.
10 is even number.
*/
Find Largest and Smallest Number in an Array Example
/*
  Find Largest and Smallest Number in an Array Example
  This Java Example shows how to find largest and smallest number in an
  array.
*/
public class FindLargestSmallestNumber {

    public static void main(String[] args) {

        //array of 10 numbers
        int numbers[] = new int[]{32,43,53,54,32,65,63,98,43,23};

        //assign first element of an array to largest and smallest
        int smallest = numbers[0];
        int largetst = numbers[0];

        for(int i=1; i< numbers.length; i++)
        {
            if(numbers[i] > largetst)
                largetst = numbers[i];
            else if (numbers[i] < smallest)
                smallest = numbers[i];

        }

        System.out.println("Largest Number is : " + largetst);
        System.out.println("Smallest Number is : " + smallest);
    }
}

/*
Output of this program would be
Largest Number is : 98
Smallest Number is : 23
*/

Java Factorial Example
/*
  Java Factorial Example
  This Java Factorial Example shows how to calculate factorial of
  a given number using Java.
*/

public class NumberFactorial {

    public static void main(String[] args) {

        int number = 5;

        /*
         * Factorial of any number is !n.
         * For example, factorial of 4 is 4*3*2*1.
        */

        int factorial = number;

        for(int i =(number - 1); i > 1; i--)
        {
            factorial = factorial * i;
        }

        System.out.println("Factorial of a number is " + factorial);
    }
}
 
/*
Output of the Factorial program would be
Factorial of a number is 120
*/
Java Factorial Using Recursion Example
Submitted By: Naresh
/*
    Java Factorial Using Recursion Example
    This Java example shows how to generate factorial of a given number
    using recursive function.
*/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class JavaFactorialUsingRecursion {

    public static void main(String args[]) throws NumberFormatException, IOException{

        System.out.println("Enter the number: ");

        //get input from the user
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(br.readLine());

        //call the recursive function to generate factorial
        int result= fact(a);


        System.out.println("Factorial of the number is: " + result);
    }

    static int fact(int b)
    {
        if(b <= 1)
            //if the number is 1 then return 1
            return 1;
        else
            //else call the same function with the value - 1
            return b * fact(b-1);
    }
}

/*
Output of this Java example would be

Enter the number:
5
Factorial of the number is: 120
*/
Java Interface example
/*
Java Interface example.
This Java Interface example describes how interface is defined and
being used in Java language.

Syntax of defining java interface is,
<modifier> interface <interface-name>{
  //members and methods()
}
*/

//declare an interface
interface IntExample{

  /*
  Syntax to declare method in java interface is,
  <modifier> <return-type> methodName(<optional-parameters>);
  IMPORTANT : Methods declared in the interface are implicitly public and abstract.
  */

  public void sayHello();
  }
}
/*
Classes are extended while interfaces are implemented.
To implement an interface use implements keyword.
IMPORTANT : A class can extend only one other class, while it
can implement n number of interfaces.
*/

public class JavaInterfaceExample implements IntExample{
  /*
  We have to define the method declared in implemented interface,
  or else we have to declare the implementing class as abstract class.
  */

  public void sayHello(){
    System.out.println("Hello Visitor !");
  }

  public static void main(String args[]){
    //create object of the class
    JavaInterfaceExample javaInterfaceExample = new JavaInterfaceExample();
    //invoke sayHello(), declared in IntExample interface.
    javaInterfaceExample.sayHello();
  }
}

/*
OUTPUT of the above given Java Interface example would be :
Hello Visitor !
*/
Reverse Number using Java
/*
  Reverse Number using Java
  This Java Reverse Number Example shows how to reverse a given number.
*/

public class ReverseNumber {

    public static void main(String[] args) {

        //original number
        int number = 1234;
        int reversedNumber = 0;
        int temp = 0;

        while(number > 0){

            //use modulus operator to strip off the last digit
            temp = number%10;

            //create the reversed number
            reversedNumber = reversedNumber * 10 + temp;
            number = number/10;

        }

        //output the reversed number
        System.out.println("Reversed Number is: " + reversedNumber);
    }
}

/*
Output of this Number Reverse program would be
Reversed Number is: 4321
*/
Swap Numbers Java Example
/*
    Swap Numbers Java Example
    This Swap Numbers Java Example shows how to
    swap value of two numbers using java.
*/

public class SwapElementsExample {

    public static void main(String[] args) {

        int num1 = 10;
        int num2 = 20;

        System.out.println("Before Swapping");
        System.out.println("Value of num1 is :" + num1);
        System.out.println("Value of num2 is :" +num2);

        //swap the value
        swap(num1, num2);
    }

    private static void swap(int num1, int num2) {

        int temp = num1;
        num1 = num2;
        num2 = temp;

        System.out.println("After Swapping");
        System.out.println("Value of num1 is :" + num1);
        System.out.println("Value of num2 is :" +num2);

    }
}

/*
Output of Swap Numbers example would be
Before Swapping
Value of num1 is :10
Value of num2 is :20
After Swapping
Value of num1 is :20
Value of num2 is :10
*/
Swap Numbers Without Using Third Variable Java Example
/*
    Swap Numbers Without Using Third Variable Java Example
    This Swap Numbers Java Example shows how to
    swap value of two numbers without using third variable using java.
*/

public class SwapElementsWithoutThirdVariableExample {

    public static void main(String[] args) {

        int num1 = 10;
        int num2 = 20;

        System.out.println("Before Swapping");
        System.out.println("Value of num1 is :" + num1);
        System.out.println("Value of num2 is :" +num2);

        //add both the numbers and assign it to first
        num1 = num1 + num2;
        num2 = num1 - num2;
        num1 = num1 - num2;

        System.out.println("Before Swapping");
        System.out.println("Value of num1 is :" + num1);
        System.out.println("Value of num2 is :" +num2);
    }


}

/*
Output of Swap Numbers Without Using Third Variable example would be
Before Swapping
Value of num1 is :10
Value of num2 is :20
Before Swapping
Value of num1 is :20
Value of num2 is :10
*/

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