Oracle Senior Application Developer Interview Questions and Answers

Q1. Run length encoding
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Q2. Find element in sorted matrix
Ans. 
Efficiently locate an element in a sorted 2D matrix using binary search or a stair-step approach.
• Use binary search on each row if the matrix is sorted row-wise.

• For a matrix sorted both row-wise and column-wise, start from the top-right corner.

• If the current element is greater than the target, move left; if less, move down.

• Example: In a matrix [[1, 2, 3], [4, 5, 6], [7, 8, 9]], to find 5, start at 3 (top-right) and move...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 1 question related to DSA and then the majority of the questions were revolving around Java.

Q1. 
Convert a Binary Tree to its Sum Tree
Given a binary tree of integers, convert it to a sum tree where each node is replaced by the sum of the values of its left and right subtrees. Set leaf nodes to zero.
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Ans. 
Convert a binary tree to a sum tree by replacing each node with the sum of its left and right subtrees, setting leaf nodes to zero.
• Traverse the tree in postorder fashion to calculate the sum of left and right subtrees for each node.

• Set leaf nodes to zero by checking if a node has no children.

• Update the value of each node to be the sum of its left and right subtrees.

• Return the level order traversal of the converted sum ...read more
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Q2. What is the garbage collector in Java?
Ans. 
Garbage collector in Java is a built-in mechanism that automatically manages memory by reclaiming unused objects.
• Garbage collector runs in the background to identify and delete objects that are no longer needed.

• It helps prevent memory leaks and optimize memory usage.

• Examples of garbage collectors in Java include Serial, Parallel, CMS, and G1.
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Q3. Why is Java considered platform independent, while the Java Virtual Machine (JVM) is platform dependent?
Ans. 
Java is platform independent because it compiles code into bytecode that can run on any system with a JVM, which is platform dependent due to its reliance on the underlying hardware and operating system.
• Java code is compiled into bytecode, which can run on any system with a JVM installed.

• JVM acts as an intermediary between the Java code and the underlying hardware/OS, making it platform dependent.

• The JVM interprets the...read more
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Q4. What do you understand by marker interfaces in Java?
Ans. 
Marker interfaces in Java are interfaces with no methods, used to mark classes for special treatment.
• Marker interfaces have no methods, they simply mark a class as having a certain capability or characteristic.

• Examples of marker interfaces in Java include Serializable, Cloneable, and Remote.

• Classes implementing marker interfaces can be treated differently by the JVM or other components based on the interface they imple...read more
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Round duration - 60 Minutes
Round difficulty - Medium

In this round, I had 2 questions of DSA where I had to first explain my approach with proper compleixt analysis and then write the pseudo code for both of them. After that, I was asked some questions from Java and MVC architecture.

Q1. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
Ans. 
Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.
• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Handle get and put operations efficiently to maintain ...read more
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Q2. 
Intersection of Linked List Problem
You are provided with two singly linked lists containing integers, where both lists converge at some node belonging to a third linked list.
Your task is to determine t...read more
Ans. 
Find the node where two linked lists merge, return -1 if no merging occurs.
• Traverse both lists to find their lengths and the difference in lengths

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

• Traverse both lists simultaneously until they meet at the merging point
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Q3. Can you explain in brief the role of different MVC components?
Ans. 
MVC components include Model, View, and Controller for organizing code in a web application.
• Model: Represents the data and business logic of the application.

• View: Represents the UI and presentation layer of the application.

• Controller: Acts as an intermediary between Model and View, handling user input and updating the Model accordingly.

• Example: In a web application, a user interacts with the View (UI), which sends requ...read more
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Q4. How is routing handled in the MVC pattern?
Ans. 
Routing in MVC pattern is handled by a routing engine which maps incoming URLs to specific controller actions.
• Routing is the process of matching incoming URLs to specific controller actions in the MVC pattern.

• Routes are defined in a routing table which maps URLs to corresponding controller actions.

• The routing engine uses the routing table to determine which controller and action should handle a particular request.

• Route...read more
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Q5. Is it possible to import the same class or package twice in Java, and what happens during runtime?
Ans. 
Yes, it is possible to import the same class or package twice in Java, but it will not cause any issues during runtime.
• Importing the same class or package multiple times in Java will not result in any errors or conflicts.

• The Java compiler will simply ignore duplicate imports and only include the class or package once in the compiled code.

• This behavior helps in avoiding unnecessary redundancy and keeps the code clean an...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round was inclined towards some Low Level Design Principles and some concepts from MVC.

Q1. Design a Railway Reservation System.
Ans. 
Railway Reservation System for booking train tickets.
• Users can search for trains based on source and destination stations.

• Users can select preferred train, class, and seat.

• System should handle payment processing and generate e-tickets.

• Admin panel for managing trains, schedules, and bookings.

• Integration with SMS/email notifications for updates.

• Database to store train details, user information, and booking history.
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Q2. What is Spring MVC?
Ans. 
Spring MVC is a framework used for building web applications in Java.
• Spring MVC stands for Model-View-Controller, which is a design pattern for separating concerns in a web application.

• It provides a powerful model for building flexible and loosely coupled web applications.

• It integrates with other Spring frameworks like Spring Boot, Spring Security, and Spring Data.

• It uses annotations to simplify configuration and reduc...read more
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Q3. Can you define the concept of Filters in MVC?
Ans. 
Filters in MVC are components that allow pre-processing and post-processing of requests and responses.
• Filters are used to perform common functionalities like logging, authentication, authorization, etc.

• They can be applied globally to all controllers or selectively to specific controllers or actions.

• Examples of filters include Authorization filters, Action filters, Result filters, and Exception filters.
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