Qable Software Testing Engineer Interview Questions and Answers

Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList uses dynamic arrays, while LinkedList uses doubly linked nodes for storage, affecting performance and use cases.
• ArrayList is backed by a dynamic array, allowing fast random access (O(1)). Example: accessing an element at index 5 is quick.

• LinkedList consists of nodes that hold data and references to the next and previous nodes, making insertions/removals faster (O(1)) when at known positions.

• ArrayList has a fi...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? Can you explain how the ReentrantLock compares to synchronized?
Ans. 
Java's synchronized keyword offers simple thread safety but has limitations compared to ReentrantLock's flexibility and features.
• Advantages of synchronized: Simple to use, built-in language feature.

• Disadvantages of synchronized: Can lead to thread contention, no timeout options.

• ReentrantLock allows for more advanced features like tryLock() and timed lock acquisition.

• Example of synchronized: synchronized void method() {...read more
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Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
Ans. 
In Java, '==' checks reference equality, while '.equals()' checks value equality. Use them appropriately to avoid bugs.
• == compares object references, checking if both refer to the same memory location.

• Example: String a = new String('test'); String b = new String('test'); a == b returns false.

• .equals() compares the actual content of the objects.

• Example: a.equals(b) returns true because the content is the same.

• Use '==' f...read more
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Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
Ans. 
Java's garbage collector automatically manages memory by reclaiming unused objects, improving performance and preventing memory leaks.
• Java uses automatic garbage collection to manage memory, freeing developers from manual memory management.

• The main garbage collection algorithms in Java include: Serial, Parallel, Concurrent Mark-Sweep (CMS), and G1 (Garbage-First).

• The Serial GC is a simple, single-threaded collector sui...read more
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Q5. What are the main features of Java 8? Can you explain how lambdas and the Stream API have changed the way Java applications are written?
Ans. 
Java 8 introduced lambdas, Stream API, and other features that enhance functional programming and improve code readability.
• Lambda Expressions: Allow concise representation of single-method interfaces (functional interfaces). Example: (x, y) -> x + y.

• Stream API: Facilitates functional-style operations on collections. Example: list.stream().filter(x -> x > 10).collect(Collectors.toList()).

• Default Methods: Enable...read more
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Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
Ans. 
Checked exceptions must be declared or handled, while unchecked exceptions do not require explicit handling.
• Checked exceptions are subclasses of Exception but not of RuntimeException.

• Example: IOException, SQLException are checked exceptions.

• Unchecked exceptions are subclasses of RuntimeException.

• Example: NullPointerException, ArrayIndexOutOfBoundsException are unchecked exceptions.

• Checked exceptions must be caught or d...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? How does volatile help ensure memory visibility?
Ans. 
The Java Memory Model defines how threads interact through memory, ensuring visibility and ordering of shared variables.
• The Java Memory Model (JMM) specifies how threads interact through memory and what behaviors are allowed.

• It ensures visibility of shared variables across threads, preventing stale data issues.

• Synchronization mechanisms (like synchronized blocks) enforce mutual exclusion and visibility.

• The 'volatile' k...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
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Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList uses dynamic arrays, while LinkedList uses linked nodes. Choose based on performance needs for insertion and access.
• ArrayList is backed by a dynamic array, allowing fast random access (O(1)). Example: accessing elements by index.

• LinkedList is backed by a doubly linked list, allowing fast insertions and deletions (O(1)) at both ends. Example: adding/removing elements from the front.

• ArrayList has a fixed size, ...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? Can you explain how the ReentrantLock compares to synchronized?
Ans. 
Java's synchronized keyword offers thread safety but has limitations compared to ReentrantLock.
• Advantages of synchronized: Simple to use, built-in language feature.

• Disadvantages of synchronized: Can lead to deadlocks, less flexible than ReentrantLock.

• ReentrantLock allows for tryLock() method, enabling non-blocking attempts to acquire a lock.

• ReentrantLock supports fairness policies, allowing threads to acquire locks in ...read more
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Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
Ans. 
In Java, '==' checks reference equality, while '.equals()' checks value equality. Use them appropriately to avoid bugs.
• == compares object references, checking if both refer to the same memory location.

• Example: String a = new String('test'); String b = new String('test'); a == b returns false.

• .equals() compares the actual content of the objects.

• Example: a.equals(b) returns true because the content is the same.

• Use '==' f...read more
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Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
Ans. 
Java's garbage collector automatically manages memory by reclaiming unused objects, improving performance and preventing memory leaks.
• Java uses automatic garbage collection to manage memory, freeing developers from manual memory management.

• The main types of garbage collection algorithms in Java include: Serial, Parallel, Concurrent Mark-Sweep (CMS), and G1 (Garbage-First).

• The Serial Garbage Collector is simple and suit...read more
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Q5. What are the main features of Java 8? Can you explain how lambdas and the Stream API have changed the way Java applications are written?
Ans. 
Java 8 introduced lambdas, Stream API, and other features that enhance functional programming and simplify code.
• Lambdas: Enable concise representation of functional interfaces. Example: (x, y) -> x + y.

• Stream API: Facilitates functional-style operations on collections. Example: list.stream().filter(x -> x > 10).collect(Collectors.toList()).

• Default Methods: Allow adding new methods to interfaces without breakin...read more
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Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
Ans. 
Checked exceptions must be declared or handled, while unchecked exceptions do not require explicit handling in Java.
• Checked exceptions are subclasses of Exception (excluding RuntimeException). Example: IOException.

• Unchecked exceptions are subclasses of RuntimeException. Example: NullPointerException.

• Checked exceptions must be either caught using try-catch or declared in the method signature with 'throws'.

• Unchecked exce...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? How does volatile help ensure memory visibility?
Ans. 
The Java Memory Model defines how threads interact through memory, ensuring visibility and ordering of shared variables.
• The Java Memory Model (JMM) specifies how threads interact with memory, ensuring consistency and visibility.

• It defines rules for visibility, atomicity, and ordering of operations in a multithreaded environment.

• Without proper synchronization, threads may see stale or inconsistent data due to caching an...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
Ans. 
Method overloading allows multiple methods with the same name but different parameters; overriding replaces a superclass method in a subclass.
• Method Overloading: Same method name, different parameter types or counts.

• Example of Overloading: 'void add(int a, int b)' and 'void add(double a, double b)'.

• Use Overloading for convenience and readability when methods perform similar functions.

• Method Overriding: Redefining a met...read more
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Mcq

Q1. How do you debug a piece of code with errors
Ans. 
Debugging involves identifying, isolating, and fixing errors in code through systematic analysis and testing.
• 1. Read error messages carefully: They often indicate the line number and type of error.

• 2. Use print statements: Insert print statements to check variable values at different execution points.

• 3. Utilize a debugger: Step through the code line by line to observe the flow and state of variables.

• 4. Check for common ...read more
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Q2. How do you keep your technical skills updated
Ans. 
I stay updated through continuous learning, hands-on projects, and engaging with the tech community.
• Participate in online courses on platforms like Coursera or Udemy to learn new technologies.

• Attend local meetups and conferences to network and learn from industry experts.

• Contribute to open-source projects on GitHub to gain practical experience and collaborate with others.

• Follow tech blogs, podcasts, and YouTube channel...read more
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Coding test duration is 30 to 40 min
on paper pen and topic is simple like related to string,pattern and number's

Q1. Introduction about yourself
Ans. 
I'm a passionate software developer with a strong background in full-stack development and a love for problem-solving.
• Experience in JavaScript frameworks like React and Angular.

• Developed a full-stack application for a local business, improving their online presence.

• Strong understanding of algorithms and data structures, demonstrated through competitive programming.

• Collaborated in Agile teams, participating in daily sta...read more
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Q2. Salary expectation
Ans. 
I expect a competitive salary based on my skills, experience, and industry standards.
• Research industry standards: For example, Glassdoor or Payscale can provide insights into average salaries for similar roles.

• Consider my experience: With 5 years in software development, I would expect a salary in the range of $80,000 to $100,000.

• Location matters: Salaries can vary significantly based on the cost of living in different...read more
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Q1. Related to the basic of html css and js
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Q2. Ask run time short code and explanation
Ans. 
Runtime refers to the period when a program is executing, affecting performance and resource usage.
• Runtime is when code is executed, as opposed to compile time.

• Performance can vary based on algorithms used; e.g., O(n) vs O(n^2).

• Memory usage is crucial; e.g., using arrays vs linked lists can impact runtime.

• Dynamic typing in languages like Python can lead to slower runtime compared to statically typed languages like C++.
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Q1. About yourself and other
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Q2. All about company your expectation and salary disscuced
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Q1. Introduced Yourself
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Q2. About knowledge in Software Development
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Q1. Write a mongoDB query to filter top 5 students
Ans. 
Use MongoDB's aggregation framework to filter and sort students by their scores, returning the top 5 results.
• Use the `find()` method to query the students collection.

• Sort the results by the score field in descending order.

• Limit the results to 5 using the `limit()` method.

• Example: `db.students.find().sort({ score: -1 }).limit(5)`

• Ensure the score field exists and is indexed for better performance.
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Q2. What is redux and difference between redux and context api
Ans. 
Redux is a state management library for JavaScript apps, while Context API is a built-in React feature for managing state.
• Redux provides a centralized store for application state, while Context API allows for state sharing across components without prop drilling.

• Redux uses actions and reducers to manage state changes, whereas Context API uses the Provider and Consumer pattern.

• Redux is more suitable for large applicatio...read more
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