Introduction: Why Java Is Needed for Automation Testing
Java is the most important programming language for software testers, especially those aiming for automation testing and SDET roles. In today’s interviews, testers are expected to know Core Java concepts along with Selenium automation, not just manual testing theory.
Java is required in testing because:
- Automation frameworks are built using Core Java
- Java supports Object-Oriented Programming (OOP), essential for framework design
- Platform-independent and stable
- Works seamlessly with Selenium, TestNG, JUnit, Cucumber, Rest Assured
- Supports UI, API, Database, and CI/CD automation
That’s why core java interview questions for testing are a must-prepare topic for manual testers, automation testers, and fresh SDETs.
Core Java Topics for Testing (Must-Know Areas)
Interviewers usually evaluate testers on these Core Java fundamentals.
1. OOP Concepts
- Class & Object
- Inheritance
- Polymorphism
- Encapsulation
- Abstraction
2. Java Collections
- List → ArrayList, LinkedList
- Set → HashSet
- Map → HashMap, LinkedHashMap
3. Exception Handling
- try, catch, finally
- Checked vs Unchecked exceptions
4. Multithreading (Basic Level)
- Thread class
- Runnable interface
5. Java 8 Features
- Streams
- Lambda expressions
- forEach()
Core Java Interview Questions for Testing (With Answers & Code)
Q1. Why is Core Java important for testing?
Core Java is used to write automation scripts, design frameworks, manage test data, and integrate tools.
Q2. What is JVM?
JVM (Java Virtual Machine) executes Java bytecode and makes Java platform-independent.
Q3. What is OOP?
Object-Oriented Programming organizes code into reusable objects.
Q4. Explain inheritance with example.
class Browser {
void open() {
System.out.println(“Browser opened”);
}
}
class Chrome extends Browser {
void test() {
System.out.println(“Testing application in Chrome”);
}
}
public class Demo {
public static void main(String[] args) {
Chrome c = new Chrome();
c.open();
c.test();
}
}
Output
Browser opened
Testing application in Chrome
Q5. What is polymorphism?
Same method name behaving differently (method overloading or overriding).
class Login {
void login() {
System.out.println(“Login with password”);
}
void login(String otp) {
System.out.println(“Login with OTP”);
}
}
Q6. What is encapsulation?
Wrapping data using private variables and accessing them through public methods.
Q7. Difference between abstract class and interface?
| Abstract Class | Interface |
| Can have method body | Methods abstract by default (Java 7) |
| Constructor allowed | No constructor |
| Partial abstraction | Full abstraction |
Q8. What is ArrayList?
A dynamic array that allows duplicate elements.
Q9. ArrayList vs LinkedList?
- ArrayList → Faster access
- LinkedList → Faster insertion/deletion
Q10. What is HashMap?
HashMap<String,String> map = new HashMap<>();
map.put(“env”,”QA”);
System.out.println(map.get(“env”));
Output
QA
Q11. Checked vs Unchecked exceptions?
- Checked → IOException
- Unchecked → NullPointerException
Q12. Exception handling example.
try {
int a = 10 / 0;
} catch (ArithmeticException e) {
System.out.println(“Exception handled”);
}
Output
Exception handled
Q13. What is multithreading?
Executing multiple threads simultaneously.
Q14. Thread vs Runnable?
Runnable is preferred because Java does not support multiple inheritance.
Q15. Java 8 Stream example.
List<Integer> list = Arrays.asList(10,20,30);
list.stream().filter(x -> x > 15).forEach(System.out::println);
Output
20
30
Selenium + Core Java Interview Questions for Testing
Q16. What is Selenium?
Selenium is an open-source tool used to automate web applications.
Q17. What is WebDriver?
WebDriver controls browsers directly using browser drivers.
Q18. Selenium code to open browser.
WebDriver driver = new ChromeDriver();
driver.get(“https://example.com”);
Q19. What are locators?
Locators identify web elements.
Types:
- id
- name
- className
- xpath
- cssSelector
Q20. XPath vs CSS Selector?
XPath supports backward traversal; CSS is faster and simpler.
Q21. Implicit vs Explicit wait.
driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(10));
WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
wait.until(ExpectedConditions.visibilityOf(element));
Java Selenium Coding Challenges (Interview Level)
Q22. Handle dropdown.
Select select = new Select(driver.findElement(By.id(“country”)));
select.selectByVisibleText(“India”);
Q23. Handle alert.
Alert alert = driver.switchTo().alert();
alert.accept();
Q24. Take screenshot.
File src = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
Q25. Find all links on a page.
List<WebElement> links = driver.findElements(By.tagName(“a”));
System.out.println(links.size());
Q26. File handling example.
BufferedReader br = new BufferedReader(new FileReader(“data.txt”));
System.out.println(br.readLine());
Real-Time Interview Scenarios for Automation Testers
Scenario 1: Page Object Model (POM)
- Base class → WebDriver setup
- Page classes → Locators & actions
- Test classes → Assertions
- Utilities → Config, reports
Scenario 2: Login Automation Test
- Launch browser
- Enter credentials
- Click Login
- Validate dashboard page
Scenario 3: API + UI Validation
- Call login API
- Capture token
- Validate UI data with API response
Scenario 4: Database Validation
- Fetch data from database
- Compare with UI displayed values
JUnit Interview Questions for Testing
Q27. What is JUnit?
JUnit is a unit testing framework for Java.
Q28. Common JUnit annotations?
- @Test
- @Before
- @After
TestNG Interview Questions for Testing
Q29. What is TestNG?
TestNG is an advanced testing framework inspired by JUnit.
Q30. Important TestNG annotations?
- @Test
- @BeforeMethod
- @AfterMethod
- @BeforeSuite
Q31. DataProvider example.
@DataProvider
public Object[][] loginData() {
return new Object[][] {{“user”,”pass”}};
}
Q32. TestNG priority example.
@Test(priority = 1)
public void loginTest() {}
Selenium + Java + API Practical Example
Response response = RestAssured.get(“/users”);
System.out.println(response.getStatusCode());
Output
200
Framework Design Interview Questions (Very Important)
Q33. What is Hybrid Framework?
Combination of POM + Data-Driven + Keyword-Driven frameworks.
Q34. What is Cucumber?
BDD framework using Gherkin syntax (Given-When-Then).
Q35. CI/CD tools used in testing?
- Jenkins
- GitHub Actions
- Azure DevOps
Common Mistakes in Core Java Testing Interviews
- Weak Core Java fundamentals
- No hands-on Selenium coding
- Hard-coded test data
- Missing waits and exception handling
- Poor framework understanding
1-Page Revision Table / Notes
| Area | Key Focus |
| Core Java | OOP, Collections, Streams |
| Selenium | Locators, Waits |
| TestNG/JUnit | Annotations, DataProvider |
| Framework | POM, Hybrid, Cucumber |
| API | Rest Assured |
| CI/CD | Jenkins |
FAQs – Core Java Interview Questions for Testing
Q1. Is Core Java mandatory for automation testing?
Yes, Core Java is the backbone of automation frameworks.
Q2. Are Java coding questions asked in testing interviews?
Yes, Core Java and Selenium coding questions are very common.
Q3. Is TestNG better than JUnit for automation testing?
Yes, TestNG supports parallel execution and advanced reporting.
Q4. Do testers need API testing knowledge?
Yes, modern testing roles expect API testing skills.