What is an alert/How to handle alert in selenium.

Alert is a common scenario for all the testers.For example if you are performing an action on a specific button like delete or save then you will  get an alert box.
If you doing a registration on a website.Then you can get an alert box.This came for your confirmation.In this scenario I am going to tell you all when I clicked on delete button of my web application i get this alert box.Then i will tell How to handle this alert box.

Web Driver provides a more efficient manner to handle all these events through the Alert interface, using the following methods:
There are four methods to work with alertbox.
void dismiss();
void accept();
String getText();
void sendKeys(String keysToSend);

Case1:
How to click on cancel on alert Box?
If you want to click on cancel button then  use void.dismiss(); 
//click on delete button
driver.findElement(By.id('id of Delete button')).click(); 
Alert myAlert = driver.switchTo().alert(); //Switch to alert pop-up
myAlert.dismiss();//click on cancel button
Case2:
How to click on ok on alert Box?
If you want to click on ok button then  use void accept();
driver.findElement(By.id('id of Delete button')).click(); 
//click on delete button
Alert myAlert = driver.switchTo().alert(); //Switch to alert pop-up
myAlert.accept(); //click on ok button

Case3:
How to getText from alert Box?
If you want to getText from pop up.

//click on delete button
driver.findElement(By.id('id of Delete button')).click(); 
Alert myAlert= driver.switchTo().alert();//Switch to alert pop-up
System.out.println(myAlert.getText());

Case4:
How to enter keys in alert box and click on ok?
If you want to enter keys in alert box.

//click on delete button
driver.findElement(By.id('id of Delete button')).click(); 
Alert myAlert=driver.switchTo().alert();//Switch to alert pop-up
driver.switchTo().myAlert().sendKeys("Delete");//This will enter keys in Textbox
myAlert.accept();//click on ok button

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