Amazon Software Engineer Interview Questions, Process, and Tips for Freshers

Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList and LinkedList are both classes in Java that implement the List interface, but they have different underlying data structures.
• ArrayList uses a dynamic array to store elements, providing fast random access but slower insertion and deletion.

• LinkedList uses a doubly linked list to store elements, providing fast insertion and deletion but slower random access.

• Choose ArrayList when you need fast random access and ...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. 
Using Java's synchronized keyword for thread synchronization has advantages like simplicity and disadvantages like potential for deadlock. ReentrantLock offers more flexibility and control.
• Advantages of synchronized keyword: simplicity, built-in support in Java

• Disadvantages of synchronized keyword: potential for deadlock, lack of flexibility

• ReentrantLock advantages: more flexibility, ability to try and lock with timeou...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, == compares memory addresses while .equals() compares the actual values of objects.
• Use == to compare primitive data types or to check if two objects reference the same memory location.

• Use .equals() to compare the actual values of objects, especially for String comparisons.

• Improper usage can lead to unexpected results, such as comparing objects instead of their values.
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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 garbage collector manages memory by automatically deallocating memory that is no longer in use.
• Java garbage collector runs in the background and identifies objects that are no longer reachable by the application.

• It uses different algorithms like Mark-Sweep, Mark-Compact, and Copying to reclaim memory.

• Mark-Sweep algorithm identifies and marks objects for deletion, then sweeps through and deallocates them.

• Mark-Compa...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 features like lambdas and Stream API which have revolutionized the way Java applications are written.
• Lambdas allow for more concise and readable code by enabling functional programming style.

• Stream API provides a way to process collections of objects in a functional way, allowing for easier parallel processing and improved performance.

• Java 8 also introduced default methods in interfaces, allowing for ...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 handled at compile time, while unchecked exceptions do not need to be caught or declared.
• Checked exceptions are subclasses of Exception class, while unchecked exceptions are subclasses of RuntimeException class.

• Checked exceptions must be caught or declared in the method signature using 'throws', while unchecked exceptions do not have this requirement.

• Examples of checked exceptions include IOE...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 and how synchronization ensures visibility and consistency.
• Java Memory Model specifies how threads interact with memory

• Synchronization ensures visibility and consistency of shared data among threads

• Volatile keyword ensures changes made by one thread are immediately visible to other threads

• Example: Using volatile keyword to share a boolean flag among mult
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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 is when multiple methods have the same name but different parameters, while method overriding is when a subclass provides a specific implementation of a method in its superclass.
• Method overloading is achieved within the same class by having multiple methods with the same name but different parameters.

• Method overriding occurs in a subclass that provides a specific implementation of a method that is al...read more
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Q9. What are functional interfaces in Java? How do they work with lambda expressions? Provide an example of a custom functional interface.
Ans. 
Functional interfaces in Java are interfaces with a single abstract method. They can be used with lambda expressions for functional programming.
• Functional interfaces have only one abstract method, but can have multiple default or static methods.

• Lambda expressions can be used to implement the abstract method of a functional interface concisely.

• An example of a custom functional interface is 'Calculator' with a single abs
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Q10. What is a Java Stream, and how does it differ from an Iterator? Explain how Streams can be used to process collections efficiently.
Ans. 
Java Stream is a sequence of elements that supports functional-style operations. It differs from Iterator by being more declarative and allowing for parallel processing.
• Java Stream is a high-level abstraction over collections that allows for functional-style operations like map, filter, reduce, etc.

• Streams are more declarative compared to Iterators, which are imperative. This means that with Streams, you specify what y...read more
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Q11. Explain the concept of immutability in Java. How does the String class achieve immutability, and what are the advantages of immutable objects?
Ans. 
Immutability in Java means objects cannot be modified after creation. String class achieves immutability by not allowing changes to its value.
• Immutability means once an object is created, its state cannot be changed.

• String class in Java is immutable because its value cannot be modified once it is assigned.

• Advantages of immutable objects include thread safety, security, and ease of caching.
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Q12. What is the difference between final, finally, and finalize in Java? Provide examples to illustrate their usage.
Ans. 
final, finally, and finalize have different meanings in Java.
• final is a keyword used to restrict the user from changing the value of a variable, making it a constant.

• finally is a block of code that is always executed, whether an exception is thrown or not.

• finalize is a method used for cleanup operations before an object is garbage collected.
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Q13. Explain the Singleton design pattern in Java. How can you implement it safely to ensure thread safety?
Ans. 
Singleton design pattern ensures a class has only one instance and provides a global point of access to it.
• Create a private static instance of the class within the class itself.

• Provide a public static method to access the instance, creating it if necessary.

• Make the constructor private to prevent instantiation from outside the class.

• Use synchronized keyword or double-checked locking to ensure thread safety.
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Q14. What are Java annotations, and how are they used in frameworks like Spring? Explain the difference between built-in and custom annotations.
Ans. 
Java annotations are metadata that provide data about a program but do not affect the program itself. They are used in frameworks like Spring to configure and customize behavior.
• Java annotations are used to provide metadata about classes, methods, fields, etc. in a program.

• In frameworks like Spring, annotations are used to configure various aspects of the application, such as dependency injection, transaction managemen...read more
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Q15. How do Java Streams handle parallel processing? What are the potential pitfalls of using parallel streams, and how can they be mitigated?
Ans. 
Java Streams can handle parallel processing using parallel streams. Pitfalls include increased complexity and potential for race conditions.
• Java Streams can be processed in parallel by calling the parallel() method on a stream.

• Potential pitfalls of using parallel streams include increased complexity, potential for race conditions, and performance overhead due to thread management.

• To mitigate these pitfalls, ensure that...read more
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Q16. 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) complexi...read more
Ans. 
ArrayList is preferred for frequent retrieval operations due to fast random access, while LinkedList is suitable for frequent insertions/deletions with fast O(1) complexity.
• Use ArrayList for scenarios where frequent retrieval operations are needed, such as searching for elements in a large collection.

• Choose LinkedList when frequent insertions/deletions are required, like maintaining a queue or stack with dynamic size.

• C...read more
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Q17. 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 pr...read more
Ans. 
ReentrantLock should be used instead of synchronized when more flexibility and control over locking mechanisms is required.
• Use ReentrantLock when you need to implement advanced locking mechanisms like tryLock() or lockInterruptibly()

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

• Explicit unlocking in ReentrantLock can help prevent deadlocks and improve performa
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Q18. 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
Ans. 
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 actual content of objects in user-defined classes.

• Override hashCode() method alongside equals() to ensure consistent behavior in collections like HashMap.

• Implement Comparable interface and override compareTo() method for natural ordering of objects.
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Q19. 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
Ans. 
Garbage collection in Java automatically reclaims memory occupied by unused objects using different GC algorithms and memory regions.
• Force garbage collection in Java can be done using System.gc() or Runtime.gc() methods.

• It is generally not recommended to force garbage collection as it can disrupt the JVM's natural memory management process and cause performance issues.

• Forcing garbage collection may not guarantee immedi...read more
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Q20. 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. ...read more
Ans. 
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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Q1. In an array where all elements are repeated twice, find an element that is repeated once
Ans. 
Find the element that is repeated once in an array where all elements are repeated twice
• Iterate through the array and use a hashmap to keep track of the count of each element

• Once the iteration is complete, check the hashmap for the element with a count of 1
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Q2. Find the maximum diagonal sum of a binary tree
Ans. 
Find the maximum diagonal sum of a binary tree
• Traverse the tree diagonally and keep track of the sum at each diagonal level

• Use a hashmap to store the sum at each diagonal level

• Return the maximum sum from the hashmap
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Q1. DSA question. Detect Symmetric Binary tree.
Ans. 
Detect if a binary tree is symmetric.
• Check if the left and right subtrees are mirror images of each other.

• Use a recursive approach to compare corresponding nodes.

• Base case: if both nodes are null, return true.

• If one node is null and the other is not, return false.

• If the values of the nodes are not equal, return false.

• Recursively check if the left subtree of the left node is symmetric to the right subtree of the right n...read more
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Q2. Merge point of twi linked list.
Ans. 
Finding the merge point of two linked lists.
• Traverse both linked lists to find their lengths.

• Move the pointer of the longer list ahead by the difference in lengths.

• Iterate both lists simultaneously until the merge point is found.
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Q1. DSA only with higher difficulty with SDE3.
Ans. 
The question is about advanced data structures and algorithms for a senior software engineer role.
• Focus on advanced data structures like AVL trees, B-trees, and tries

• Discuss complex algorithms like Dijkstra's algorithm, A* search algorithm, and dynamic programming

• Highlight experience with optimizing time and space complexity

• Provide examples of solving challenging coding problems or implementing complex algorithms
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Q1. System Design and Project.
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Basic data structure and algorithm problem

Q1. Basic data structrure and algo problems
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Q2. Cant share exact questions due to legal reasons
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