使用Selenium时收到“线程“ main” java.lang.NullPointerException中的异常”

Question

When using this class in Selenium WebDriver:

package Selenium3;

import java.util.ArrayList;
import java.util.List;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;

public class Jobs {

static WebDriver driver;

public Jobs(WebDriver driver) {
    this.driver = driver;
}

public static void con() throws InterruptedException {
    List<WebElement> element = driver.findElements(By.cssSelector(".position_title.ng-binding"));
    for (int i = 0; i < element.size(); i++) {
        Thread.sleep(2000);
        String u = element.get(i).getText();
        if (u.contains("Java"));
        System.out.println(u);
    }
  }
}

The driver is always null. In the end I want to call this method from my Main class. What am I doing wrong?

Answer 1

You have an static method (that not requires class instantiation)... so when you call the method without instantiating the class you wont initialize your driver:

You have various solutions:

• Make method not static (you will force initialization of driver with constructor, but you can reuse the instantiated class various times)

   public class Jobs { private WebDriver driver; public Jobs(WebDriver driver) { this.driver = driver; } public void con() throws InterruptedException { List<WebElement> element = driver.findElements(By.cssSelector(".position_title.ng-binding")); for (int i = 0; i < element.size(); i++) { Thread.sleep(2000); String u = element.get(i).getText(); if (u.contains("Java")); System.out.println(u); } } 

• Keep method static adding driver as a parameter (so you will have your driver prior to call method and you won't need to instantiate the class)

   public class Jobs { public static void con(WebDriver driver) throws InterruptedException { List<WebElement> element = driver.findElements(By.cssSelector(".position_title.ng-binding")); for (int i = 0; i < element.size(); i++) { Thread.sleep(2000); String u = element.get(i).getText(); if (u.contains("Java")); System.out.println(u); } } 

• Use a static block to initialize the driver prior the method static call (faster to call, but problem is you cannot chuoose which driver implementation you will use)

   public class Jobs { static WebDriver driver; static { this.driver = new FirefoxDriver(); // just an example } public static void con() throws InterruptedException { List<WebElement> element = driver.findElements(By.cssSelector(".position_title.ng-binding")); for (int i = 0; i < element.size(); i++) { Thread.sleep(2000); String u = element.get(i).getText(); if (u.contains("Java")); System.out.println(u); } }