在Selenium WebDriver中获取java.lang.NullPointerException

Question

在Eclipse中运行testcase时，我将获得java.lang.NullPointerException。有人能帮我指出我犯的错误吗？

错误@Line 17:loginpage.java中的WebElement。@Line 12:tc_logineTwin_001.java中的LoginPage。

**LoginPage.Java**

package com.internetBanking.pageObjects;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;

public class LoginPage {
    
    WebDriver driver;
    
    public LoginPage (WebDriver driver) {
            
        this.driver = driver;
        
    }
    
    WebElement usrname = driver.findElement(By.name("uid"));
    WebElement pwd = driver.findElement(By.name("password"));
    WebElement login = driver.findElement(By.name("btnLogin"));
    
    public void setUsrname(String uname) {
        usrname.sendKeys(uname);
    }

    public void setPwd(String pswd) {
        pwd.sendKeys(pswd);
    }

    public void login() {
        
        login.click();
    }

}

**TC_LoginTest_001.java**

package com.internetBanking.testCases;
import org.testng.annotations.Test;
import com.internetBanking.pageObjects.LoginPage;
public class TC_LoginTest_001 extends BaseClass {
    
    @Test
    public void LoginTest() {
                
        driver.get(baseURL);
        logger.info("URL is opened");
        
        LoginPage loginPage = new LoginPage(driver);
        
        loginPage.setUsrname(username);
        logger.info("Username is entered");
        
        loginPage.setPwd(password);
        logger.info("Password is entered");
        
        loginPage.login();                                         
        logger.info("Login button is clicked");
        
    }
}

当我运行测试用例时，我得到以下错误：

java.lang.NullPointerException在com.internetbanking.pageobjects.loginpage.(loginpage.java:17)在com.internetbanking.testcases.tc_logineter_001.java:12)在sun.reflect.nativeMethodAccessorImpl.Invoke0（原生方法）在sun.reflect.nativeMethodAccessorImpl.Invoke（未知源）在sun.reflect.delegatingmethodAccessorImpl.Invoke（未知源）在r.runtest(Suiterunner.java:455)在org.testng.suiterunner.runsequency(Suiterunner.java:450)在org.testng.suiterunner.privaterun(Suiterunner.java:415)在org.testng.suiterunner.java:364)在org.testng.suiterunner.runsuite(Suiterunner.java:52)在org.testng.suiterunnerworker.runsuite(Suiterunner.java:52)在

Answer 1

请考虑以下代码：

public class MainTest {
    public static void main(String[] args) {
        new Test(new Object());
    }
}

class Test {
    InitMe initMe = new InitMe();
    public Test(Object o){
        System.out.println("Test instance has been created");
    }
}

class InitMe{
    public InitMe(){
        System.out.println("Init me instance has been created");
    }
}

如果运行它,您将看到以下输出：

Init me instance has been created
Test instance has been created

这意味着在执行构造函数之前初始化字段。因此在您的情况下,您有以下结构：

public class MainTest {
    public static void main(String[] args) {
        new Test(new Object());
    }
}

class Test {
    Object o;
    String oStr = o.toString();
    public Test(Object o){
        this.o = o;
    }
}

    WebDriver driver;
    
    public LoginPage (WebDriver driver) {
            
        this.driver = driver;
        
    }
    
    WebElement usrname = driver.findElement(By.name("uid"));
    WebElement pwd = driver.findElement(By.name("password"));
    WebElement login = driver.findElement(By.name("btnLogin"));

    WebDriver driver;
    WebElement usrname;
    WebElement pwd;
    WebElement login;
    
    public LoginPage (WebDriver driver) {
        this.driver = driver;
        usrname = driver.findElement(By.name("uid"));
        pwd = driver.findElement(By.name("password"));
        login = driver.findElement(By.name("btnLogin"));}
    }