java - 获取以下代码段的Java NPE。不确定出什么问题了

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What is a NullPointerException, and how do I fix it?

（12个答案）


5年前关闭。

import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.datatransfer.StringSelection;
import java.awt.event.KeyEvent;

import org.openqa.selenium.By;
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;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;

public class EmployeeTest {

@FindBy(xpath="//input[@id='email']")
public static WebElement emailIDField;

@FindBy(xpath="//input[@id='password']")
public static WebElement passwordField;

@FindBy(xpath="//a[@id='submitButton']")
public static WebElement loginButton;

static String subscriptionsAndBillingTabXpath="//a[contains(text(),'Silling')]";
@FindBy(xpath="//a[contains(text(),'Silling')]")
public static WebElement subscriptionsAndBillingTab;

public static WebDriver driver;

public static WebDriverWait wait;

public static void main(String[] args) {
    // TODO Auto-generated method stub
    driver = new FirefoxDriver();

    driver.get("http://url.domain.com");

    wait.until(ExpectedConditions.visibilityOf(emailIDField));
    emailIDField.click();
    emailIDField.sendKeys("[email protected]");

    wait.until(ExpectedConditions.visibilityOf(passwordField));
    passwordField.click();
    passwordField.sendKeys("xyz");

    loginButton.click();

    wait.until(ExpectedConditions.visibilityOf(subscriptionsAndBillingTab));
    if(driver.findElements(By.xpath(subscriptionsAndBillingTabXpath)).size()!=0)
        System.out.println("Login successful!");

    else
        System.out.println("Failed to login!");
    driver.close();

}

}

下面是例外情况，

Exception in thread "main" java.lang.NullPointerException
    at org.openqa.selenium.support.ui.ExpectedConditions.elementIfVisible(ExpectedConditions.java:227)
    at org.openqa.selenium.support.ui.ExpectedConditions.access$1(ExpectedConditions.java:226)
    at org.openqa.selenium.support.ui.ExpectedConditions$7.apply(ExpectedConditions.java:213)
    at org.openqa.selenium.support.ui.ExpectedConditions$7.apply(ExpectedConditions.java:1)
    at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:208)
    at EmployeeTest.main(EmployeeTest.java:43)

最佳答案

您尚未初始化wait，因此其为null并在下一行上抛出NPE

wait.until(ExpectedConditions.visibilityOf(emailIDField));

您可以将其初始化为

wait = new WebDriverWait(driver, 15);

这里的15是超时值（以秒为单位），您可以根据需要进行更改。您也可以使用documentation中提供的其他构造函数。