Introduction: Why Java Is Needed for Automation Testing
Java is the most widely used programming language in automation testing. Almost every enterprise-level automation framework is built using Java + Selenium + TestNG/JUnit + CI/CD tools.
In automation interviews, Java is not tested like a developer role. Instead, interviewers focus on:
- Applying Core Java concepts to automation problems
- Designing maintainable automation frameworks
- Handling UI, API, and database validation
- Writing clean, reusable automation code
That’s why automation testing Java technical interview questions form the backbone of QA and SDET interviews.
Core Java Topics for Testing
1. Object-Oriented Programming (OOP)
Used for:
- Framework architecture
- Code reusability
- Maintainability
Key concepts:
- Encapsulation
- Inheritance
- Polymorphism
- Abstraction
2. Collections Framework
Used to store:
- Test data
- API responses
- Database values
- WebElements
Common collections:
- List
- Set
- Map
3. Multithreading
Used for:
- Parallel execution in TestNG
- Faster regression cycles
4. Exception Handling
Used to:
- Handle Selenium failures
- Improve stability
- Debug automation issues
5. Java 8 Streams
Used for:
- Filtering test data
- Validating API and DB results
- Cleaner utility methods
Automation Testing Java Technical Interview Questions (With Answers)
Core Java Interview Questions (1–25)
1. Why is Java preferred for automation testing?
Java is platform-independent, object-oriented, scalable, and integrates easily with automation tools.
2. Explain OOP concepts with automation relevance.
- Encapsulation → Secure test data
- Inheritance → Base test classes
- Polymorphism → Browser-independent execution
- Abstraction → Framework layers
3. Encapsulation example:
class Config {
private String browser = “chrome”;
public String getBrowser() {
return browser;
}
}
Expected Output:
Browser value accessed using getter method.
4. Inheritance example:
class BaseTest {
void setup() {
System.out.println(“Setup completed”);
}
}
class LoginTest extends BaseTest {
void execute() {
setup();
System.out.println(“Login test executed”);
}
}
Output:
Setup completed
Login test executed
5. How is polymorphism used in Selenium?
A single WebDriver reference is used to run tests on different browsers.
6. Abstract class vs interface?
| Abstract Class | Interface |
| Partial abstraction | Full abstraction |
| Can have methods | Used as contract |
7. What is a singleton class in automation?
Ensures only one instance of WebDriver or configuration class.
8. Why is String immutable?
For security, performance, and thread safety.
9. String vs StringBuilder vs StringBuffer?
| Type | Thread Safe | Performance |
| String | Yes | Slow |
| StringBuilder | No | Fast |
| StringBuffer | Yes | Medium |
10. What is exception handling?
Handling runtime errors without terminating execution.
11. Checked vs unchecked exceptions?
| Checked | Unchecked |
| Compile time | Runtime |
| IOException | NullPointerException |
12. Custom exception example:
class FrameworkException extends RuntimeException {
FrameworkException(String msg) {
super(msg);
}
}
13. Why are collections important in automation?
They store dynamic test data and results efficiently.
14. ArrayList vs HashSet?
| ArrayList | HashSet |
| Allows duplicates | No duplicates |
| Maintains order | No order |
15. HashMap usage example:
Map<String,String> data = new HashMap<>();
data.put(“username”,”admin”);
16. Iterating HashMap:
for(Map.Entry<String,String> e : data.entrySet()) {
System.out.println(e.getKey()+” : “+e.getValue());
}
Output:
username : admin
17. What is multithreading?
Executing multiple threads concurrently.
18. Why multithreading in automation?
To execute tests in parallel.
19. Thread vs Runnable?
Runnable is preferred for better design.
20. What is synchronization?
Controls access to shared resources.
21. Java 8 Stream example:
List<Integer> list = Arrays.asList(1,2,3,4);
list.stream().filter(n -> n%2==0).forEach(System.out::println);
Output:
2
4
22. File handling usage?
Reading config files and test data.
23. File read example:
BufferedReader br = new BufferedReader(new FileReader(“data.txt”));
System.out.println(br.readLine());
24. What is garbage collection?
Automatic memory management.
25. What are access modifiers?
public, private, protected, default.
Java Selenium Coding Challenges (26–55)
26. Launch browser dynamically:
WebDriver driver;
if(browser.equals(“chrome”)) {
driver = new ChromeDriver();
}
27. Locator priority?
id → name → cssSelector → xpath
28. Dynamic XPath example:
//input[contains(@id,’email’)]
29. Types of waits?
Implicit, Explicit, Fluent.
30. Explicit wait example:
WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
wait.until(ExpectedConditions.elementToBeClickable(By.id(“login”)));
31. Thread.sleep vs Explicit wait?
| Thread.sleep | Explicit Wait |
| Static | Dynamic |
| Not recommended | Recommended |
32. Handle dropdown:
Select s = new Select(element);
s.selectByVisibleText(“India”);
33. Handle alert:
driver.switchTo().alert().accept();
34. Handle frames:
driver.switchTo().frame(“frame1”);
35. Handle multiple windows?
Using getWindowHandles().
36. Screenshot on failure:
File src = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
37. StaleElementReferenceException?
Element removed from DOM.
38. Solution?
Re-locate the element.
39. Actions class usage?
Mouse hover, drag and drop.
40. JavaScriptExecutor usage?
Handle hidden elements.
41. Headless browser?
Used in CI/CD.
42. Selenium Grid?
Parallel cross-browser execution.
43. Selenium limitation?
Cannot automate CAPTCHA.
44. Page Object Model (POM)?
Separates UI logic and test logic.
45. POM example:
@FindBy(id=”username”)
WebElement username;
46. Hybrid framework?
POM + Data-driven + Keyword-driven.
47. Framework folder structure?
base, pages, tests, utils, reports.
48. Test data management?
Excel, JSON, DB.
49. Read properties file:
Properties prop = new Properties();
prop.load(new FileInputStream(“config.properties”));
50. Maven usage?
Dependency and build management.
51. Maven lifecycle?
clean → test → install
52. Jenkins role?
CI/CD automation.
53. Git usage?
Version control.
54. Logging tool?
Log4j.
55. Reporting tools?
Extent Reports, Allure.
JUnit & TestNG Interview Questions (56–75)
56. Why TestNG is preferred?
Parallel execution and advanced annotations.
57. Common TestNG annotations?
| Annotation | Purpose |
| @Test | Test case |
| @BeforeMethod | Setup |
| @AfterMethod | Teardown |
58. DataProvider example:
@DataProvider
public Object[][] data() {
return new Object[][]{{“admin”,”123″}};
}
59. Hard vs Soft assertion?
| Hard | Soft |
| Stops execution | Continues |
60. TestNG XML usage?
Controls execution flow.
61. Grouping tests?
Execute selected test groups.
62. DependsOnMethods?
Controls test dependency.
63. Retry Analyzer?
Re-runs failed tests.
64. Listener usage?
Captures test execution events.
65. Parallel execution?
Thread count in XML.
66. JUnit annotations?
@Test, @Before, @After
67. JUnit vs TestNG?
| JUnit | TestNG |
| Simple | Advanced |
68. Parameterization?
Multiple test data sets.
69. BDD framework?
Cucumber.
70. Feature file?
Written in Gherkin.
71. Step definition?
Maps steps to code.
72. Hooks?
@Before, @After
73. CI/CD integration?
Automated execution.
74. API testing tool?
REST Assured.
75. API validations?
Status code, response body.
Selenium + Java + API + DB Scenarios (76–90)
76. API + DB validation scenario:
Create data via API and validate in DB.
77. JDBC connection example:
Connection con = DriverManager.getConnection(url,user,pass);
78. Execute query:
ResultSet rs = stmt.executeQuery(“SELECT * FROM USERS”);
79. UI + DB validation?
Compare UI and DB values.
80. API + UI validation?
Create data via API and verify in UI.
81. Parallel execution challenge?
Thread safety.
82. Handling flaky tests?
Explicit waits and retries.
83. Environment handling?
Config files.
84. Logging importance?
Debugging failures.
85. Reporting importance?
Stakeholder visibility.
86. CI/CD failure handling?
Auto rerun with logs.
87. Security testing?
Limited via Selenium.
88. Performance testing?
Handled by JMeter.
89. Framework scalability?
Modular design.
90. Maintenance strategy?
Reusable utilities.
Common Mistakes in Java Automation Interviews
- Weak OOP explanation
- No framework clarity
- Memorised answers
- Poor exception handling
- No real-time examples
1-Page Revision Table / Notes
| Area | Key Focus |
| Core Java | OOP, Collections |
| Selenium | Locators, Waits |
| TestNG | Parallel execution |
| Framework | POM, Hybrid |
| CI/CD | Jenkins |
FAQs (For Google Ranking)
Is Java mandatory for automation testing?
Yes, Java is the most widely used language.
Are framework questions compulsory?
Yes, especially POM and Hybrid.
Is API + DB testing required?
Yes, end-to-end testing is common.
Is coding required in interviews?
Yes, basic to intermediate Java coding is expected.