eAppSys Interview Questions and Answers

Q1. Sale price on on day
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Q2. Start working
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Q1. Basics like introduction background
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Q2. Introduce yourself
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Q3. What is your background
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Q1. Interview are very simple and average person can clear huge hiring
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Q1. 1. Screening 2. Introduction interview basic questions 3. Voice assessment 4. Written assignment 5. Confery test 6. Operation test 7. If qualified final manager round List looks scary to crack but v...read more
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Q1. Explain the difference between ArrayList and LinkedList in Java. ArrayList is implemented as a dynamic array, while LinkedList is a doubly linked list. ArrayList provides fast random access (O(1) complexit...read more
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ArrayList is preferred for frequent retrieval operations due to fast random access, while LinkedList is suitable for frequent insertions/deletions.
• Use ArrayList when frequent retrieval operations are required, such as searching for elements in a large collection.

• Choose LinkedList when frequent insertions/deletions are needed, like maintaining a queue or stack.

• Consider memory overhead and performance trade-offs when dec...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? The synchronized keyword ensures that only one thread can access a block of code at a time. It pre...read more
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ReentrantLock should be used instead of synchronized when more flexibility and control over locking mechanisms is needed.
• Use ReentrantLock when you need to implement custom locking strategies or require advanced features like tryLock() and lockInterruptibly().

• ReentrantLock supports fair locking mechanisms, ensuring that threads acquire the lock in the order they requested it.

• Explicit unlocking in ReentrantLock reduces ...read more
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Q3. What is the difference between == and .equals() in Java? == checks for reference equality, meaning it compares memory addresses. equals() checks for value equality, which can be overridden in user-defined ...read more
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In Java, == checks for reference equality while equals() checks for value equality. Misuse of == can lead to logical errors.
• Override equals() when you want to compare the values of objects instead of their references

• Override hashCode() alongside equals() to ensure proper functioning in collections like HashMap

• Consider implementing Comparable interface for natural ordering in collections
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Q4. How does the Java garbage collector work? Garbage collection in Java automatically reclaims memory occupied by unused objects. The JVM has different types of GC algorithms, including Serial, Parallel, CMS,...read more
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Garbage collection in Java automatically reclaims memory occupied by unused objects using different algorithms and memory regions.
• Java garbage collector automatically reclaims memory from unused objects

• Different types of GC algorithms in JVM: Serial, Parallel, CMS, G1 GC

• Objects managed in Young Generation, Old Generation, and PermGen/Metaspace

• Minor GC cleans up short-lived objects in Young Generation

• Major GC (Full GC) ...read more
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Q5. What are the main features of Java 8? Java 8 introduced lambda expressions, enabling functional-style programming. The Stream API allows efficient data processing with map, filter, and reduce operations. D...read more
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Lambda expressions in Java 8 improve readability and maintainability by enabling concise and functional-style programming.
• Lambda expressions allow writing more compact code by reducing boilerplate code.

• They enable passing behavior as arguments to methods, making code more modular and flexible.

• Example: (a, b) -> a + b is a lambda expression that adds two numbers.
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Q6. Describe the differences between checked and unchecked exceptions in Java. Checked exceptions must be handled using try-catch or declared with throws. Unchecked exceptions (RuntimeException and its subclas...read more
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Checked exceptions must be handled explicitly, while unchecked exceptions do not require explicit handling.
• Use custom exceptions when you want to create your own exception types to handle specific scenarios.

• Custom exceptions can be either checked or unchecked, depending on whether you want to enforce handling or not.

• For example, a custom InvalidInputException could be a checked exception if you want to ensure it is cau...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? The Java Memory Model (JMM) defines how threads interact with shared memory. It ensures visibility and ordering of ...read more
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The Java Memory Model defines how threads interact with shared memory, ensuring visibility and ordering of variable updates in a concurrent environment.
• Volatile keyword ensures changes to a variable are always visible to all threads.

• Synchronized keyword provides mutual exclusion and visibility guarantees.

• Reordering optimizations by the compiler or CPU can lead to unexpected behavior.

• Happens-before relationship determin...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Method overloading allows multiple methods with the same name but different parameters. It occurs within the same cl...read more
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Method overloading allows multiple methods with the same name but different parameters, while method overriding allows a subclass to provide a different implementation of a parent method.
• Use method overloading when you want to provide multiple ways to call a method with different parameters.

• Use method overriding when you want to provide a specific implementation of a method in a subclass.

• Example of method overloading: ...read more
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Q9. What are functional interfaces in Java, and how do they work with lambda expressions? A functional interface is an interface with exactly one abstract method. Examples include Runnable, Callable, Predicate...read more
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Functional interfaces in Java have exactly one abstract method and work with lambda expressions for concise implementation.
• Functional interfaces have exactly one abstract method, such as Runnable, Callable, Predicate, and Function.

• Lambda expressions provide a concise way to implement functional interfaces.

• Default methods in interfaces help in evolving APIs without breaking backward compatibility.

• Method references (::) ...read more
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Q10. What is a Java Stream, and how does it differ from an Iterator? Streams enable functional-style operations on collections with lazy evaluation. Unlike Iterators, Streams support declarative operations lik...read more
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Java Streams enable functional-style operations on collections with lazy evaluation, unlike Iterators.
• Parallel streams can improve performance by utilizing multiple threads, but may introduce overhead due to thread management.

• Care must be taken to ensure thread safety when using parallel streams in a multi-threaded environment.

• Parallel streams are suitable for operations that can be easily parallelized, such as map and...read more
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Q11. Explain the concept of immutability in Java and its advantages. An immutable object cannot be changed after it is created. The String class is immutable, meaning modifications create new objects. Immutabl...read more
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Immutability in Java prevents objects from being changed after creation, promoting thread safety and preventing unintended side effects.
• Immutable objects cannot be modified after creation, promoting thread safety

• String class in Java is immutable, modifications create new objects

• Use final fields and avoid setters to create immutable classes

• Collections can be made immutable using Collections.unmodifiableList()

• Immutabilit...read more
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Q12. What is the difference between final, finally, and finalize in Java? final is a keyword used to declare constants, prevent method overriding, or inheritance. finally is a block that executes after a try-c...read more
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final, finally, and finalize have different meanings in Java. final is for constants, finally for cleanup, and finalize for garbage collection.
• final is used for constants, preventing method overriding, and inheritance

• finally is used for cleanup actions after a try-catch block

• finalize() is called by the garbage collector before object deletion

• Alternatives to finalize() for resource management include using try-with-reso...read more
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Q13. Explain the Singleton design pattern in Java. Singleton ensures that only one instance of a class exists in the JVM. It is useful for managing shared resources like database connections. A simple implemen...read more
Ans. 
Singleton design pattern ensures only one instance of a class exists in the JVM, useful for managing shared resources like database connections.
• Avoid using Singleton when multiple instances of a class are required.

• Avoid Singleton for classes that are not thread-safe.

• Avoid Singleton for classes that need to be easily mockable for testing purposes.
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Q14. What are Java annotations, and how are they used in frameworks like Spring? Annotations provide metadata to classes, methods, and fields. @Override, @Deprecated, and @SuppressWarnings are common built-in ...read more
Ans. 
Java annotations provide metadata to classes, methods, and fields, improving code readability and maintainability.
• Annotations like @Component, @Service, and @Autowired in Spring help with dependency injection

• Annotations reduce boilerplate code compared to XML configurations

• Custom annotations can be created using @interface

• Reflection APIs allow reading annotation metadata dynamically

• Annotations like @Transactional simpl
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Q15. How do Java Streams handle parallel processing, and what are its pitfalls? Parallel streams divide data into multiple threads for faster processing. The ForkJoin framework handles parallel execution inter...read more
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Java Streams handle parallel processing by dividing data into multiple threads using the ForkJoin framework. Pitfalls include race conditions, performance issues with small datasets, and debugging challenges.
• Parallel streams divide data into multiple threads for faster processing

• ForkJoin framework handles parallel execution internally

• Useful for CPU-intensive tasks but may not improve performance for small datasets

• Share...read more
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Q1. Self intro and project architecture
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Q2. What are the data sources used?
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Q3. Bigquery architecture
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Q4. Partition vs clustering
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Q5. Bq commands on create table and load csv file
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Q6. Bq commands on show the schema of the table
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Q7. Explain about leaf nodes and columnar storage.
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Q8. How many slots are there in bigquery?
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A sequence was provided: 4181, 2684, 1597, 987, 610.
first 2 are given and write code for other value calculation using java 8

The second question required writing a reverse of a palindrome using both Java 8 streams. I was able to successfully write both and clear the first round.

Q1. Interviewer was himself not knowing anything as it was walkin drive he was sitting infront of me and checking questions on phone Introduction that he inturrepted in between when I was introducing myself
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Q2. What are the features of Java 17, specifically related to sealed classes, including their syntax and necessity, along with the potential errors encountered when invoking a sealed class?
Ans. 
Java 17 introduces sealed classes to restrict inheritance and improve code maintainability.
• Sealed classes are declared using the 'sealed' keyword followed by the permitted subclasses.

• Subclasses of a sealed class must be either final or sealed themselves.

• Errors may occur when trying to extend a sealed class with a non-permitted subclass.
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Q3. Java 8 feathers stream api, functional interface, Intermittent operator ,Ternary operator, Prediction,Bi predicate. Answered all successfully
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Q4. Draw low level design of implementation of notify me if item is back in stock in a ecommerce application
Ans. 
Implementation of 'notify me if item is back in stock' feature in an ecommerce application
• Create a database table to store user notifications for out-of-stock items

• Implement a service to check item availability and send notifications to subscribed users

• Provide a user interface for users to subscribe to notifications for specific items
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Q5. All design patterns which I know. Asked me to implement adapter pattern on paper
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Q6. Then given a problem that concurrent way perform operation on excell to decrease the response time
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