SELENIUM TESTNG: Difference between @Factory and @DataProvider

SELENIUM TESTNG: Difference between @Factory and @DataProvider:

DataProvider: A test method that uses DataProvider will be executed a multiple number of times based on the data provided by the DataProvider. The test method will be executed using the same instance of the test class to which the test method belongs.

Factory: A factory will execute all the test methods present inside a test class using a separate instance of the respective class.
TestNG factory is used to create instances of test classes dynamically. This is useful if you want to run the test class any number of times. For example, if you have a test to login into a site and you want to run this test multiple times,then its easy to use TestNG factory where you create multiple instances of test class and run the tests (may be to test any memory leak issues). 

                Whereas, dataprovider is used to provide parameters to a test. If you provide dataprovider to a test, the test will be run taking different sets of value each time. This is useful for a scenario like where you want to login into a site with different sets of username and password each time.

@DataProvider with @Factory:

The @DataProvider feature can also be used with the @Factory annotation for creating tests at runtime. This can be done by declaring the @Factory annotation on a constructor of a class or on a regular method.

Example :

 package com.rameshsoft.rameshselenium;

import org.testng.annotations.DataProvider;

import org.testng.annotations.Factory;

import org.testng.annotations.Test;

public class DataProviderWithFactory

{

    private int param_value;

    @Factory(dataProvider = "dataMethod")

    public DataProviderWithFactory(int param) {

        this.param_value = param;

    }

    @DataProvider

    public static Object[][] dataMethod() {

        return new Object[][] { { 0}, { 1} };

    }

    @Test

    public void testMethodOne() {

        int value = param_value + 1;

        System.out.println("Test method one output: "+ value);

    }

    @Test

    public void testMethodTwo() {

        int value = param_value + 2;

        System.out.println("Test method two output: "+ value);

    }

}

output:

Test method one output: 1

Test method one output: 2

Test method two output: 2

Test method two output: 3