Question 1

Explain the four OOP pillars and where you used them in your automation framework.

Accepted Answer

Encapsulation, inheritance, polymorphism and abstraction. In a Selenium framework, page objects encapsulate locators, a BaseTest/BasePage provides inheritance, WebDriver references give polymorphism, and interfaces like WebDriver itself are abstraction.

Question 2

What is the difference between method overloading and overriding?

Accepted Answer

Overloading is the same method name with different parameter lists in the same class, resolved at compile time. Overriding is a subclass redefining a parent method with the same signature, resolved at runtime.

Question 3

String vs StringBuilder vs StringBuffer?

Accepted Answer

String is immutable, so every modification creates a new object. StringBuilder is mutable and not synchronized (fast), StringBuffer is mutable and synchronized (thread-safe but slower).

Question 4

Which collections do you use in automation and why?

Accepted Answer

List (ArrayList) for ordered elements such as findElements results, Set (HashSet) to detect duplicates or store window handles, and Map (HashMap) for test data and config key-value pairs.

Question 5

What are checked vs unchecked exceptions? Name common Selenium exceptions.

Accepted Answer

Checked exceptions are verified at compile time and must be handled or declared (IOException). Unchecked exceptions extend RuntimeException and are not enforced by the compiler; all Selenium exceptions are unchecked.

Question 6

Difference between final, finally and finalize?

Accepted Answer

final is a keyword making variables constant, methods non-overridable and classes non-inheritable. finally is a block that always runs after try/catch, used for cleanup like driver.quit(). finalize() was a GC hook, deprecated since Java 9.

Question 7

What does static mean and where do you use it in a framework?

Accepted Answer

static members belong to the class rather than an instance, so they are shared and accessible without creating an object. Frameworks use it for utility methods, constants and config loaders.

Question 8

Interface vs abstract class: when do you use each?

Accepted Answer

An interface defines a contract a class can implement (many allowed), with default/static methods since Java 8. An abstract class can hold state, constructors and partial implementation, but a class can extend only one.

Question 9

What are generics and how do they help in test utilities?

Accepted Answer

Generics provide compile-time type safety by parameterizing classes and methods with types. They let you write reusable utilities, like a JSON deserializer or fluent page navigation, without casting.

Question 10

How do you use streams and lambdas in automation?

Accepted Answer

Streams let you filter, map and collect collections declaratively, and lambdas provide concise implementations of functional interfaces. They're great for processing lists of WebElements or API response data.

Question 11

TestNG vs JUnit 5: key annotations and differences?

Accepted Answer

Both are test frameworks. TestNG offers groups, dependsOnMethods, DataProvider and XML-driven parallel suites; JUnit 5 uses a modular Jupiter API with @ParameterizedTest, extensions and tags.

Question 12

Hard assert vs soft assert?

Accepted Answer

A hard assert stops the test immediately on failure. A soft assert collects failures and reports them all when assertAll() is called, useful for validating many fields on one page.

Question 13

What is Maven and how do you run tests with it?

Accepted Answer

Maven is a build and dependency management tool driven by pom.xml. Tests run in the test phase via the Surefire plugin, so mvn test or mvn clean test executes the suite, typically in CI.

Question 14

How does HashMap work internally?

Accepted Answer

HashMap stores entries in an array of buckets indexed by the key's hashCode. Collisions are chained in a linked list that becomes a balanced tree after 8 entries (Java 8+); equals() finds the exact key.

Question 15

How do you use ThreadLocal in Java to give each parallel test its own WebDriver?

Accepted Answer

Wrap the driver in ThreadLocal so each thread gets its own instance. A DriverManager sets it in @BeforeMethod, reads it via get(), and calls quit() then remove() in @AfterMethod.

Question 16

Which design patterns have you used in your framework?

Accepted Answer

Page Object Model for UI structure, Factory for creating browser drivers, Singleton for config readers, Builder for test data and Strategy for swapping behaviors like environments.

Question 17

Write a program to reverse a string without using built-in reverse.

Accepted Answer

Iterate from the last character to the first and append to a StringBuilder, or swap characters in a char array using two pointers. Both run in O(n).

Question 18

Find duplicate elements in an array.

Accepted Answer

Add each element to a HashSet; if add() returns false the element is a duplicate. This is O(n) time compared to O(n^2) with nested loops.

Question 19

Check whether a string is a palindrome.

Accepted Answer

Compare characters from both ends moving inward; if any pair differs it's not a palindrome. Normalize case and strip non-alphanumerics first for phrases.

Question 20

Count the frequency of each character (or word) using a HashMap.

Accepted Answer

Loop through the characters and use map.merge(c, 1, Integer::sum) to increment counts. A LinkedHashMap preserves first-occurrence order in the output.

Question 21

What is the difference between JDK, JRE and JVM?

Accepted Answer

The JVM executes bytecode and makes Java platform independent. The JRE is the JVM plus core libraries needed to run programs, and the JDK is the JRE plus development tools like javac, jar and javadoc.

Question 22

What are primitive types vs wrapper classes, and what is autoboxing?

Accepted Answer

Java has eight primitives (byte, short, int, long, float, double, char, boolean) stored as raw values, and matching wrapper classes like Integer that are objects. Autoboxing converts primitives to wrappers automatically and unboxing does the reverse.

Question 23

What is the equals() and hashCode() contract in Java?

Accepted Answer

If two objects are equal by equals(), they must return the same hashCode(). Unequal objects may share a hash code, but good distribution keeps HashMap and HashSet fast.

Question 24

Explain Java access modifiers and how you apply them in page objects.

Accepted Answer

private is visible only inside the class, default (no modifier) within the package, protected within the package plus subclasses, and public everywhere. Page objects keep locators private and expose public action methods.

Question 25

How do constructors, this() and super() work in Java?

Accepted Answer

A constructor initializes a new object and has the class name with no return type. this() calls another constructor of the same class, super() calls the parent constructor, and either must be the first statement.

Question 26

What is the difference between an array and an ArrayList?

Accepted Answer

An array has a fixed size and can hold primitives or objects. An ArrayList is a resizable List implementation backed by an array that holds only objects and offers methods like add, remove and contains.

Question 27

Write a FizzBuzz program in Java.

Accepted Answer

Loop from 1 to n and print FizzBuzz for multiples of 15, Fizz for multiples of 3, Buzz for multiples of 5, otherwise the number. Check 15 first, or the 3 and 5 branches will win.

Question 28

Swap two numbers without using a third variable in Java.

Accepted Answer

Use arithmetic: a = a + b, b = a - b, a = a - b. XOR swapping also works and avoids overflow concerns for integers.

Question 29

Reverse an integer and find the sum of its digits in Java.

Accepted Answer

Repeatedly take the last digit with n % 10, add it to the result (rev * 10 + digit for reversal, sum + digit for the sum), then drop it with n / 10 until n is 0.

Question 30

Print the Fibonacci series up to n terms in Java.

Accepted Answer

Start with 0 and 1, and each next term is the sum of the previous two. An iterative loop is O(n); naive recursion is O(2^n) and should be avoided for large n.

Question 31

Check whether a number is prime and print primes up to n in Java.

Accepted Answer

A prime is greater than 1 and divisible only by 1 and itself. Check divisors from 2 up to the square root of n; if none divide evenly, it is prime.

Question 32

Compare ArrayList, LinkedList, HashSet, TreeSet and Vector.

Accepted Answer

ArrayList is array-backed with fast random access; LinkedList is a doubly linked list with cheap insertion at the ends. HashSet stores unique elements with no order, TreeSet keeps them sorted, and Vector is a legacy synchronized list.

Question 33

What is the difference between Comparable and Comparator?

Accepted Answer

Comparable defines a class's natural ordering via compareTo() inside the class itself. Comparator is a separate object with compare() that lets you define multiple custom orderings without changing the class.

Question 34

What is Optional in Java and how should you use it?

Accepted Answer

Optional is a container that may or may not hold a value, introduced in Java 8 to make 'no result' explicit and reduce NullPointerExceptions. Use it mainly as a method return type.

Question 35

What are functional interfaces? Name the common built-in ones.

Accepted Answer

A functional interface has exactly one abstract method, so it can be implemented with a lambda or method reference. Common ones are Predicate, Function, Consumer, Supplier and Runnable.

Question 36

What is the difference between throw and throws, and how do you create a custom exception?

Accepted Answer

throw is a statement that raises a specific exception instance, while throws in a method signature declares exceptions the method may pass to callers. A custom exception extends Exception (checked) or RuntimeException (unchecked).

Question 37

How do you create an immutable class in Java?

Accepted Answer

Make the class final, all fields private final, set them only in the constructor, provide no setters, and defensively copy mutable fields in and out. Java 16+ records give you most of this for free.

Question 38

Explain Java memory: stack vs heap and garbage collection.

Accepted Answer

Each thread has a stack holding method frames, local variables and references, while objects live on the shared heap. The garbage collector reclaims heap objects that are no longer reachable from GC roots.

Question 39

How do you write data-driven tests in JUnit 5?

Accepted Answer

Use @ParameterizedTest with a source annotation such as @ValueSource, @CsvSource, @CsvFileSource, @EnumSource or @MethodSource. Each row runs as a separate test invocation with its own report entry.

Question 40

How do you use TestNG listeners and retry failed tests?

Accepted Answer

Implement ITestListener to hook into events like onTestFailure for screenshots and reporting, and IRetryAnalyzer to rerun a failed test a fixed number of times. Register listeners via @Listeners or testng.xml.

Question 41

Check whether two strings are anagrams in Java.

Accepted Answer

Two strings are anagrams if they contain the same characters with the same counts. Either sort both char arrays and compare, which is O(n log n), or count characters with an int array, which is O(n).

Question 42

Find the second largest number in an array in a single pass.

Accepted Answer

Track largest and second largest while iterating. When a number beats the largest, shift largest down to second; otherwise update second if the number is between them and not equal to the largest.

Question 43

Find the missing number in an array containing 1 to n.

Accepted Answer

The expected sum of 1 to n is n * (n + 1) / 2; subtract the actual sum of the array and the difference is the missing number. XOR of all indices and values works too and avoids overflow.

Question 44

How do ExecutorService and CompletableFuture work in Java?

Accepted Answer

ExecutorService manages a pool of threads so you submit tasks instead of creating threads yourself, and returns Futures for results. CompletableFuture adds non-blocking composition with thenApply, thenCombine and allOf.

Question 45

Explain synchronized, volatile and concurrent collections.

Accepted Answer

synchronized gives mutual exclusion and visibility by letting only one thread hold a monitor at a time. volatile guarantees visibility of a variable's latest value across threads but not atomicity, and concurrent collections like ConcurrentHashMap provide thread-safe operations without locking the whole structure.

Question 46

Which Java 17 and 21 features do you use in test code?

Accepted Answer

Java 17 LTS brought records, sealed classes, switch expressions, text blocks and pattern matching for instanceof. Java 21 LTS added record patterns, pattern matching for switch, sequenced collections and virtual threads.

Question 47

What are virtual threads in Java 21 and do they matter for test automation?

Accepted Answer

Virtual threads are lightweight threads managed by the JVM rather than the OS, so you can run thousands of blocking tasks cheaply. They help I/O-heavy work like many parallel API calls, but don't make browser tests faster because each browser is still a heavy process.

Question 48

Sort an integer array without using Arrays.sort().

Accepted Answer

Bubble sort repeatedly swaps adjacent out-of-order elements so the largest bubbles to the end each pass. It's O(n^2) but simple; add a swapped flag to stop early when the array is already sorted.

Question 49

Find all pairs in an array whose sum equals a target.

Accepted Answer

Iterate once and keep a HashSet of numbers seen so far; for each number, if target minus it is in the set, you've found a pair. This is O(n) instead of the O(n^2) nested loop.

Question 50

How do reflection and custom annotations work in Java test frameworks?

Accepted Answer

Reflection lets code inspect and invoke classes, methods and fields at runtime, and annotations attach metadata that frameworks read through reflection. TestNG and JUnit find @Test methods this way, and you can build custom annotations like @Owner or @Jira for reporting.

Interview Questions

01Explain the four OOP pillars and where you used them in your automation framework.BeginnerOOP & Core Java

02What is the difference between method overloading and overriding?BeginnerOOP & Core Java

03String vs StringBuilder vs StringBuffer?BeginnerOOP & Core Java

04Which collections do you use in automation and why?BeginnerCollections & Generics

05What are checked vs unchecked exceptions? Name common Selenium exceptions.BeginnerExceptions

06Difference between final, finally and finalize?BeginnerExceptions

07What does static mean and where do you use it in a framework?BeginnerOOP & Core Java

08Interface vs abstract class: when do you use each?IntermediateOOP & Core Java

09What are generics and how do they help in test utilities?IntermediateCollections & Generics

10How do you use streams and lambdas in automation?IntermediateJava 8+ Features

11TestNG vs JUnit 5: key annotations and differences?IntermediateTestNG, JUnit & Maven

12Hard assert vs soft assert?IntermediateTestNG, JUnit & Maven

13What is Maven and how do you run tests with it?IntermediateTestNG, JUnit & Maven

14How does HashMap work internally?IntermediateCollections & Generics

15How do you use ThreadLocal in Java to give each parallel test its own WebDriver?IntermediateOOP & Core Java