Introduction: Why Java Is Needed for Automation Testing
Java plays a critical role in automation and database testing. Most enterprise automation frameworks are built using Java + Selenium + TestNG/JUnit + SQL. Companies expect automation testers to validate UI, backend APIs, and databases together.
In interviews that focus on 335 Java and DB testing interview questions, recruiters evaluate:
- Core Java fundamentals
- Automation testing logic
- Database validation skills
- Real-time framework usage
- End-to-end test scenarios
Java allows testers to connect UI, API, and DB layers seamlessly, making it indispensable for modern testing roles.
Core Java Topics for Testing
1. Object-Oriented Programming (OOP)
- Encapsulation
- Inheritance
- Polymorphism
- Abstraction
2. Collections Framework
- List, Set, Map
- ArrayList, HashSet, HashMap
- Iteration and data handling
3. Multithreading
- Thread class
- Runnable interface
- Parallel execution in TestNG
4. Exception Handling
- try–catch–finally
- throws vs throw
- Custom exceptions
5. Java 8 Features
- Streams
- Lambda expressions
- Functional interfaces
Java Interview Questions with Answers (1–40)
1. What is Java?
Java is a platform-independent, object-oriented programming language widely used in automation testing.
2. Why is Java used in automation testing?
- Platform independence
- Strong OOP support
- Easy integration with Selenium and DB
- Mature ecosystem
3. What is JVM?
JVM executes Java bytecode and enables write once, run anywhere.
4. Difference between JDK, JRE, JVM?
| Component | Purpose |
| JVM | Executes bytecode |
| JRE | JVM + libraries |
| JDK | JRE + compiler |
5. What are OOP concepts?
Encapsulation, Inheritance, Polymorphism, Abstraction.
6. Encapsulation example:
class User {
private String username;
public void setUsername(String name) {
username = name;
}
public String getUsername() {
return username;
}
}
Output:
Data accessed securely using getter/setter.
7. What is inheritance?
class Browser {
void open() {
System.out.println(“Browser opened”);
}
}
class Chrome extends Browser {
void launch() {
System.out.println(“Chrome launched”);
}
}
Output:
Browser opened
Chrome launched
8. What is polymorphism?
Same method name with different behavior.
9. Overloading vs overriding?
| Overloading | Overriding |
| Compile time | Runtime |
| Same class | Parent-child |
10. What is abstraction?
Hiding implementation and exposing functionality.
11. Abstract class vs interface?
| Abstract Class | Interface |
| Partial abstraction | Full abstraction |
| Can have methods | Supports multiple inheritance |
12. What is constructor?
Initializes objects automatically.
13. What is static keyword?
Belongs to class, not object.
14. What is final keyword?
Prevents modification.
15. Why String is immutable?
For security and memory optimization.
16. String vs StringBuilder?
| String | StringBuilder |
| Immutable | Mutable |
| Slow | Fast |
17. What is exception?
An abnormal event that disrupts execution.
18. Checked vs unchecked exceptions?
| Checked | Unchecked |
| Compile-time | Runtime |
| IOException | NullPointerException |
19. try vs throws?
- try handles exception
- throws declares exception
20. What is collection framework?
Used to store and manipulate data dynamically.
21. List vs Set?
- List allows duplicates
- Set does not
22. ArrayList vs LinkedList?
| ArrayList | LinkedList |
| Faster retrieval | Faster insertion |
| Uses array | Uses nodes |
23. What is HashMap?
Stores key-value pairs.
24. Iterate HashMap:
HashMap<String, Integer> map = new HashMap<>();
map.put(“ID”, 101);
for(Map.Entry<String,Integer> e : map.entrySet()) {
System.out.println(e.getKey()+” “+e.getValue());
}
Output:
ID 101
25. What is multithreading?
Executing multiple threads concurrently.
26. Why multithreading in automation?
Parallel test execution.
27. Thread vs Runnable?
Runnable supports multiple inheritance.
28. What is synchronization?
Controls thread access to shared resources.
29. 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
30. What is lambda expression?
Provides functional programming support.
31. File handling in Java?
Reading and writing files.
32. Read file example:
BufferedReader br = new BufferedReader(new FileReader(“data.txt”));
System.out.println(br.readLine());
33. Serialization?
Converting object to byte stream.
34. Deserialization?
Converting byte stream to object.
35. What is garbage collection?
Automatic memory management.
36. What is wrapper class?
Converts primitive to object.
37. What is enum?
Fixed set of constants.
38. What is package?
Namespace for classes.
39. Access modifiers?
public, private, protected, default.
40. What is singleton class?
Allows only one object.
Selenium + Java Interview Questions (41–80)
41. What is Selenium WebDriver?
Web automation tool.
42. Launch browser:
WebDriver driver = new ChromeDriver();
driver.get(“https://example.com”);
43. Locators in Selenium?
id, name, className, xpath, cssSelector.
44. XPath types?
Absolute and Relative.
45. Dynamic XPath example:
//input[contains(@id,’email’)]
46. What are waits?
Implicit, Explicit, Fluent.
47. Explicit wait example:
WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
wait.until(ExpectedConditions.visibilityOfElementLocated(By.id(“login”)));
48. Thread.sleep vs wait?
| Thread.sleep | Wait |
| Static | Dynamic |
49. Handle dropdown:
Select s = new Select(element);
s.selectByVisibleText(“India”);
50. Handle alerts:
driver.switchTo().alert().accept();
51. Handle frames?
driver.switchTo().frame(0);
52. Take screenshot?
File src = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
53. Actions class usage?
Mouse and keyboard actions.
54. Stale element exception?
Element no longer in DOM.
55. Handle multiple windows?
Using window handles.
56. What is Page Object Model?
Separates UI and test logic.
57. POM example:
@FindBy(id=”username”)
WebElement user;
58. What is Hybrid Framework?
Combination of POM + Data-driven + Keyword-driven.
59. Role of Maven?
Build and dependency management.
60. Maven lifecycle?
clean, test, install.
61. What is Jenkins?
CI/CD automation tool.
62. CI/CD in testing?
Automates test execution.
63. Selenium Grid?
Parallel cross-browser execution.
64. Limitations of Selenium?
No desktop automation.
65. Headless browser?
Browser without UI.
66. Read Excel using Java?
Apache POI.
67. Read properties file:
Properties p = new Properties();
p.load(new FileInputStream(“config.properties”));
68. Logging tool?
Log4j.
69. Reporting tools?
Extent Reports, Allure.
70. CAPTCHA handling?
Cannot be automated.
71. Upload file?
sendKeys(filePath).
72. Download file validation?
Check file system.
73. Exception handling in framework?
Centralized try-catch.
74. Retry failed tests?
Retry Analyzer.
75. Listener in TestNG?
Listens to test execution.
76. Cross-browser testing?
Run on Chrome, Firefox, Edge.
77. Handling dynamic elements?
Explicit waits.
78. Handling pop-ups?
Alerts or window switching.
79. Test data management?
Excel, JSON, DB.
80. Framework folder structure?
pages, tests, utilities, base.
Database Testing Interview Questions (81–120)
81. What is database testing?
Validating data stored in DB.
82. Why DB testing?
Ensures backend data integrity.
83. Types of DB testing?
Structural, Functional, Performance.
84. What is SQL?
Structured Query Language.
85. CRUD operations?
Create, Read, Update, Delete.
86. Select query?
SELECT * FROM users;
87. Where clause?
Filters records.
88. Join types?
Inner, Left, Right, Full.
89. Primary key?
Unique identifier.
90. Foreign key?
Links tables.
91. Normalization?
Reduces redundancy.
92. Index?
Improves query performance.
93. Stored procedure?
Reusable SQL block.
94. View?
Virtual table.
95. ACID properties?
Atomicity, Consistency, Isolation, Durability.
96. JDBC?
Java Database Connectivity.
97. JDBC connection example:
Connection con = DriverManager.getConnection(url,user,pass);
98. Execute query:
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(“SELECT * FROM users”);
99. Validate DB data with UI?
Compare UI value with DB result.
100. API + DB validation scenario?
Validate response data in DB.
Real-Time Automation Scenarios
End-to-End Scenario Example
- Create user via API
- Validate user in DB
- Login via UI
- Verify dashboard
Common Mistakes in Java & DB Interviews
- Weak SQL knowledge
- Ignoring DB validation
- No framework explanation
- Memorised answers
- No coding practice
1-Page Revision Table
| Area | Focus |
| Java | OOP, Collections |
| Selenium | Locators, Waits |
| DB | SQL, Joins |
| Framework | POM, CI/CD |
| Tools | Maven, Jenkins |
FAQs (For Google Ranking)
Are Java and DB testing both mandatory?
Yes, backend validation is essential.
How much SQL is required?
Basic to intermediate queries.
Is JDBC important?
Yes, for automation DB validation.
Which framework is preferred?
Hybrid framework.