Null Pointer Exception Error at Selenium TestNG

Question

I'm trying to automate the search box but I'm getting null pointer exception.

---

package LICT.Maven_ReCheck_Search;

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.testng.annotations.AfterTest;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;

import io.github.bonigarcia.wdm.WebDriverManager;

public class ReTest_Search {

    public WebDriver driver;
    
    @BeforeTest
    public void beforeTest() {
        WebDriverManager.chromedriver().setup();
        driver =new ChromeDriver();
        driver.manage().window().maximize();
        
        driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
    }
    
    @Test
    public void test() {
        Homepage_ReCheck_Search homepage = new Homepage_ReCheck_Search(driver);
        driver.get("http://automationpractice.com/index.php");
        homepage.input_search_keyword("T Shirt");
        homepage.input_search_submit();
        
    }
    
    @AfterTest
    public void afterTest() {
        driver.close();
    }
    
}

---

package LICT.Maven_ReCheck_Search;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

public class Homepage_ReCheck_Search {
    public WebDriver driver;

    Homepage_ReCheck_Search(WebDriver driver){
        this.driver = driver;
        PageFactory.initElements(this.driver, driver);
        
    }
    
    @FindBy(xpath ="//input[@id='search_query_top']" )
    WebElement search_box;
    
    @FindBy(xpath ="//button[@name='submit_search']" )
    WebElement search_submit;
    
    
    public void input_search_keyword(String keyword) {
        search_box.sendKeys(keyword);
        System.out.println("Input is taken");
    }
    public void input_search_submit() {
        search_submit.click();
        System.out.println("Submit is done");
    }
}

---

[RemoteTestNG] detected TestNG version 7.3.0
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Starting ChromeDriver 84.0.4147.30 (48b3e868b4cc0aa7e8149519690b6f6949e110a8-refs/branch-heads/4147@{#310}) on port 22005
Only local connections are allowed.
Please see https://chromedriver.chromium.org/security-considerations for suggestions on keeping ChromeDriver safe.
ChromeDriver was started successfully.
Aug 19, 2020 4:13:59 PM org.openqa.selenium.remote.ProtocolHandshake createSession
INFO: Detected dialect: W3C

**FAILED: test
java.lang.NullPointerException**
    at 

LICT.Maven_ReCheck_Search.Homepage_ReCheck_Search.input_search_keyword(Homepage_ReCheck_Search.java:25)
    at LICT.Maven_ReCheck_Search.ReTest_Search.test(ReTest_Search.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)
    at org.testng.internal.TestInvoker.invokeMethod(TestInvoker.java:599)
    at org.testng.internal.TestInvoker.invokeTestMethod(TestInvoker.java:174)
    at org.testng.internal.MethodRunner.runInSequence(MethodRunner.java:46)
    at org.testng.internal.TestInvoker$MethodInvocationAgent.invoke(TestInvoker.java:822)
    at org.testng.internal.TestInvoker.invokeTestMethods(TestInvoker.java:147)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:146)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:128)
    at java.util.ArrayList.forEach(Unknown Source)
    at org.testng.TestRunner.privateRun(TestRunner.java:764)
    at org.testng.TestRunner.run(TestRunner.java:585)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:384)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:378)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:337)
    at org.testng.SuiteRunner.run(SuiteRunner.java:286)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:53)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:96)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1218)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1140)
    at org.testng.TestNG.runSuites(TestNG.java:1069)
    at org.testng.TestNG.run(TestNG.java:1037)
    at org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:115)
    at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:251)
    at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:77)


===============================================
    Default test
    Tests run: 1, Failures: 1, Skips: 0
===============================================


===============================================
Default suite
Total tests run: 1, Passes: 0, Failures: 1, Skips: 0
===============================================

Answer 1

The initElements method second argument should be a page class, you feed it the driver. I think you should change the constructor of Homepage_ReCheck_Search to:

PageFactory.initElements(driver, this);

The search_box never gets initialized, because you do not init a page. Thus the search_box stays NULL its default value. Meaning you cannot interact with it.