How to scroll web page in Selenium Webdriver using java?

Scroll by given pixel offset
//To scroll down web page by 900 pixels In x(vertical) direction.   
//You can y parameter to scroll page In horizontal direction. 
JavascriptExecutor javascript = (JavascriptExecutor) driver; 
javascript.executeScript("window.scrollBy(0,900)", "");     
 
//To scroll up web page by 300 pixels In x(vertical) direction. 
javascript.executeScript("window.scrollBy(0,-300)", ""); 
Scroll down to bottom of page

//Scroll down to bottom of the page. 
  JavascriptExecutor javascript = (JavascriptExecutor) driver; 
  javascript.executeScript("window.scrollTo(0, document.body.scrollHeight)", "");   

//Scroll till element. 
JavascriptExecutor je = (JavascriptExecutor) driver; 
je.executeScript("arguments[0].scrollIntoView(true);",driver.findElement(By.partialLinkText("About Yahoo")));  

Scroll to element using Keys
Actions action = new Actions(dr); 
     action.sendKeys(Keys.PAGE_DOWN); 
     Thread.sleep(5000); 
     action.click(driver.findElement(By.partialLinkText("About Yahoo"))).perform(); 

Example:
import java.util.concurrent.TimeUnit; 
import org.openqa.selenium.By; 
import org.openqa.selenium.JavascriptExecutor; 
import org.openqa.selenium.Keys; 
import org.openqa.selenium.WebDriver; 
import org.openqa.selenium.WebElement; 
import org.openqa.selenium.firefox.FirefoxDriver; 
import org.openqa.selenium.interactions.Actions; 
   
public class ScrollDownUp { 
      public static void main(String[] args) throws InterruptedException { 
 
        // WebDriver reference but Firefox object 
        WebDriver dr = new FirefoxDriver(); 
        //Maximize browser window        
        dr.manage().window().maximize(); 
        //Go to URL       
        dr.get("https://www.yahoo.com/"); 
        //Set  timeout       
        dr.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS); 
 
        //To scroll down web page by 800 pixels In x(vertical) direction.   
        //You can y parameter to scroll page In horizontal direction. 
        JavascriptExecutor javascript = (JavascriptExecutor) dr; 
        javascript.executeScript("window.scrollBy(0,1200)", ""); 
        Thread.sleep(3000);// 
        //To scroll up web page by 300 pixels In x(vertical) direction. 
        javascript.executeScript("window.scrollBy(0,-300)", ""); 
 
        Thread.sleep(5000); 
        //Scroll down to bottom of the page. 
        JavascriptExecutor jasct = (JavascriptExecutor) dr; 
        jasct.executeScript("window.scrollTo(0, document.body.scrollHeight)", ""); 
 
        Thread.sleep(5000); 
        //Scroll till element. 
        JavascriptExecutor je = (JavascriptExecutor) dr; 
        je.executeScript("arguments[0].scrollIntoView(true);", dr.findElement(By.partialLinkText("Mail"))); 
 
        Thread.sleep(5000); 
        // Scroll till to element by Keys 
        dr.findElement(By.partialLinkText("About Yahoo")).sendKeys(Keys.PAGE_DOWN); 
        Thread.sleep(3000); 
        dr.findElement(By.partialLinkText("Mail")).sendKeys(Keys.PAGE_UP); 
 
        Thread.sleep(5000); 
        // Scroll till to element by action  
        Actions action = new Actions(dr); 
        action.sendKeys(Keys.PAGE_DOWN); 
        action.click(dr.findElement(By.partialLinkText("About Yahoo"))).perform(); 
 
        //close firefox browser   
        dr.quit(); 
    } 
}