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Amazon Software Engineer Interview Questions and Answers
78 Interview questions
Counting good triplets involves finding triplets in an array that satisfy specific conditions based on given parameters.
Definition of Good Triplet: A triplet (i, j, k) is considered good if i < j < k and arr[j] - arr[i] = arr[k] - arr[j].
Example: For the array [1, 2, 3, 4], the triplet (1, 2, 3) is good because 2 - 1 = 3 - 2 = 1.
Constraints: The problem may specify constraints on the values of i, j, and k, s...
The increasing triplet subsequence problem involves finding a subsequence of three numbers in an array that are in increasing order.
Definition: An increasing triplet subsequence is a sequence of three indices i, j, k such that i < j < k and nums[i] < nums[j] < nums[k].
Example: In the array [1, 2, 3, 4, 5], the triplet (1, 2, 3) is an increasing subsequence.
Optimal Approach: Use two variables to track t...
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
Java annotations provide metadata for classes, methods, and fields, enhancing functionality in frameworks like Spring.
Annotations are a form of metadata that provide data about a program but are not part of the program itself.
In Spring, annotations like @Autowired and @Controller simplify dependency injection and define components.
Built-in annotations include @Override, @Deprecated, and @SuppressWarnings, which se...
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ArrayList uses dynamic arrays, while LinkedList uses a doubly linked list structure for storing elements.
ArrayList is faster for random access (e.g., get(index)). Example: arrayList.get(5);
LinkedList is better for frequent insertions/deletions. Example: linkedList.addFirst('A');
ArrayList has a fixed size, while LinkedList can grow and shrink dynamically.
Memory overhead is higher for LinkedList due to node pointers...
final, finally, and finalize have different meanings in Java.
final is a keyword used to declare constants, prevent method overriding, and prevent inheritance.
finally is a block used in exception handling to execute code after try-catch block.
finalize is a method used for cleanup operations before an object is garbage collected.
In Java, == compares memory addresses while .equals() compares object contents.
Use == to compare primitive data types and object references.
Use .equals() to compare object contents, such as strings.
Improper usage can lead to unexpected results, as == may not always work as expected with objects.
Method overloading involves creating multiple methods in the same class with the same name but different parameters, while method overriding involves creating a new implementation of a method in a subclass.
Method overloading is used to provide different ways to call a method with different parameters. For example, having multiple constructors in a class with different parameter lists.
Method overriding is used to p...
Java Streams provide a functional approach to processing sequences of elements, unlike Iterators which are imperative.
Streams are part of the Java 8+ API, enabling functional-style operations on collections.
Unlike Iterators, Streams do not store data; they process data on-the-fly.
Streams support operations like map, filter, and reduce, allowing for concise and readable code.
Example: List<String> names = Arra...
In Java, == compares memory addresses while .equals() compares values of objects.
Use == to compare primitive data types and object references.
Use .equals() to compare the actual values of objects.
Improper usage can lead to unexpected results, such as comparing memory addresses instead of values.
Amazon Software Engineer Interview Experiences
80 interviews found
Anonymous
Interview Questionnaire
20 Questions
- Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
- 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 synchronized keyword for thread synchronization in Java has advantages like simplicity and disadvantages like potential for deadlock. ReentrantLock offers more flexibility and control.
Advantages of using synchronized keyword: simplicity, built-in support in Java
Disadvantages of using synchronized keyword: potential for deadlock, lack of flexibility
ReentrantLock offers more flexibility and control: ability to try ...
- Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
- Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
- Ans.
The Java garbage collector automatically manages memory by reclaiming unused objects.
Java garbage collector runs in the background, periodically identifying and removing objects that are no longer needed.
Different types of garbage collection algorithms in Java include Serial, Parallel, CMS, G1, and ZGC.
Serial garbage collector uses a single thread for garbage collection, while Parallel garbage collector uses multiple t...
- 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 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 backw...
- Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
- 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 changes made by one thread are visible to others.
Java Memory Model ensures that changes made by one thread are visible to other threads.
It defines the behavior of threads in terms of reading and writing to memory.
Synchronization in Java ensures that only one thread can access a shared resource at a time.
The 'volatile' keyword in Java ensures that...
- Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
- 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.
They can be used with lambda expressions to provide a concise way of implementing the abstract method.
An example of a custom functional interface is 'MyFunctionalInterface' with...
- Q10. What is a Java Stream, and how does it differ from an Iterator? Explain how Streams can be used to process collections efficiently.
- 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 that once an object is created, its state cannot be changed.
String class achieves immutability by making the value of the string constant and not allowing it to be changed after creation.
Advantages of immutable objects include thread safety, caching, and easier debugging.
Immutable objects are inherently thread-safe because their state cannot be modified, reducing the risk of concurrency issue...
- Q12. What is the difference between final, finally, and finalize in Java? Provide examples to illustrate their usage.
- 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.
Make the constructor private to prevent instantiation from outside the class.
Provide a public static method to access the instance, creating it if necessary.
Use synchronized keyword or double-checked locking to ensure thread safety.
- Q14. What are Java annotations, and how are they used in frameworks like Spring? Explain the difference between built-in and custom annotations.
- 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...
- 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...
- Ans.
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...
- 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...
- Ans.
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 are granted access in the order they requested it.
Explicit unlocking in ReentrantLock reduce...
- 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...
- 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 values of objects instead of their references
Override hashCode() method alongside equals() to ensure proper functioning in collections like HashMap
Implement Comparable interface if you want to define a natural ordering for objects
- 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...
- Ans.
Garbage collection in Java automatically reclaims memory occupied by unused objects using different algorithms and memory regions.
Force garbage collection in Java using System.gc() or Runtime.gc() methods.
Not recommended to force garbage collection as it can cause performance issues by disrupting the JVM's natural memory management.
Forcing garbage collection can lead to unnecessary CPU usage and potential application s...
- 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. ...
- 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.
test
Selected
I appeared for an interview in Jan 2025, where I was asked the following questions.
- Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
- 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...
- Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
- Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
- Ans.
The Java garbage collector automatically manages memory by reclaiming unused objects.
Garbage collection in Java is done by the JVM to reclaim memory occupied by objects that are no longer in use.
There are different types of garbage collection algorithms in Java such as Serial, Parallel, CMS, G1, and Z Garbage Collector.
Each algorithm has its own way of managing memory and has different performance characteristics.
For e...
- 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 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 backw...
- Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
- 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 data consistency.
Java Memory Model specifies how threads interact with memory
Synchronization ensures data consistency by preventing race conditions
Volatile keyword ensures visibility of changes made by one thread to other threads
Volatile variables are not cached locally by threads, always read from main memory
Example: Usin...
- Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
- 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...
- Q10. What is a Java Stream, and how does it differ from an Iterator? Explain how Streams can be used to process collections efficiently.
- 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 achieves immutability by making the value of the string constant and not allowing modification
Advantages of immutable objects include thread safety, caching, and ease of use
- Q12. What is the difference between final, finally, and finalize in Java? Provide examples to illustrate their usage.
- 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.
Ensure the constructor is private to prevent instantiation from outside the class.
Use synchronized keyword or double-checked locking to ensure thread safety.
- Q14. What are Java annotations, and how are they used in frameworks like Spring? Explain the difference between built-in and custom annotations.
- 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...
- 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...
- Ans.
ArrayList for frequent retrieval, LinkedList for frequent insertions/deletions.
Use ArrayList for scenarios where frequent retrieval operations are needed, such as searching or sorting large datasets.
Choose LinkedList when frequent insertions/deletions are required, like maintaining a queue or stack.
Consider memory overhead and performance trade-offs when deciding between ArrayList and LinkedList.
- 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...
- Ans.
ReentrantLock should be used instead of synchronized when more flexibility and control over locking mechanisms is needed.
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 reduces the chances of deadlocks and allows for m...
- 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...
- 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 values of objects instead of their references
Override hashCode() alongside equals() to ensure consistent behavior in collections like HashMap
Consider implementing Comparable interface for natural ordering of objects
- 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...
- Ans.
Garbage collection in Java automatically reclaims memory occupied by unused objects using different algorithms and memory regions.
Java garbage collection automatically reclaims memory from unused objects
Different types of GC algorithms in Java include Serial, Parallel, CMS, and G1 GC
Objects are managed in Young Generation, Old Generation, and PermGen/Metaspace
Minor GC cleans up short-lived objects in Young Generation
Ma...
- 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. ...
- 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.
Lambda expressions can be used with functional interfac...
(2 Questions)
- Q1. In an array where all elements are repeated twice, find an element that is repeated once
- Q2. Find the maximum diagonal sum of a binary tree
3 leetcode hards, followed by some system design
(2 Questions)
- Q1. How to design amazon
- Ans.
Designing Amazon involves creating a user-friendly e-commerce platform with a vast product selection, efficient search and recommendation algorithms, secure payment processing, and reliable delivery logistics.
Develop a user-friendly interface for easy navigation and product search
Implement recommendation algorithms based on user behavior and preferences
Integrate secure payment processing systems to protect customer inf...
- Q2. How to invert 25 bst
- Ans.
To invert a binary search tree (BST), swap the left and right children of each node recursively.
Start from the root node and recursively swap the left and right children of each node.
Repeat this process for all nodes in the BST.
The final result will be the inverted BST.
Interview Preparation Tips
Skills evaluated in this interview
The Aptitude was quite hard
The coding round was medium
(1 Question)
- Q1. They asked dsa, operating system, coding
I appeared for an interview in Mar 2025, where I was asked the following questions.
- Q1. Question:1 Count good triplets in an array
- Q2. Question:2 Increasing triplet subsequence
Selected
I applied via Naukri.com and was interviewed in May 2024. There were 3 interview rounds.
Coding questions based on DP
(2 Questions)
- Q1. Binary search based question
- Q2. Graph bfs based question
(2 Questions)
- Q1. Question related to my project
- Q2. Question based on dsa
Selected
I applied via Referral
2 coding question were asked
(2 Questions)
- Q1. Sum on node in binary tree
- Ans.
Recursively sum the values of nodes in a binary tree
Use a recursive function to traverse the tree and add the values of each node
Base case: if the current node is null, return 0
Recursive step: return the sum of current node value, left subtree sum, and right subtree sum
- Q2. Lp question asked
(2 Questions)
- Q1. Question on string manipulation
- Q2. Lp question asked
(2 Questions)
- Q1. Managerial question on projects were asked
- Q2. Past experience and leadership question
Skills evaluated in this interview
Hard and platformwas leetcode and geeksforgeeks
(2 Questions)
- Q1. Medium level code was asked
- Q2. Hard level code as asked
Interview Preparation Tips
Selected
Good, leetcode medium level questions
Amazon Interview FAQs
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