Eidiko Systems Integrators Interview Questions and Answers

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Q1. What is the servlet life cycle, and can you explain its various phases?
Ans. 
The servlet life cycle consists of initialization, request handling, and destruction phases managed by the servlet container.
• 1. Initialization: The servlet is loaded into memory and initialized by calling the init() method.

• 2. Request Handling: The servlet processes client requests through the service() method, which can handle multiple requests concurrently.

• 3. Destruction: The servlet is taken out of service and cleane...read more
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Q2. What is the purpose of the String constant pool in Java?
Ans. 
The String constant pool in Java optimizes memory usage by storing unique string literals.
• Strings are immutable in Java, meaning once created, they cannot be changed.

• The String constant pool is a special memory area in the Java heap.

• When a string literal is created, Java checks the pool first to see if it already exists.

• If it exists, a reference to the existing string is returned; if not, a new string is created.

• Exampl...read more
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Q3. If a servlet component receives 10 requests after its deployment, which methods will be executed and how many times will each be called?
Ans. 
A servlet processes requests using lifecycle methods; init, service, and destroy are key in handling multiple requests.
• init(): Called once when the servlet is first loaded; initializes resources. Example: Database connections.

• service(): Called for each request; handles the request and response. Example: Processing user input.

• destroy(): Called once when the servlet is taken out of service; cleans up resources. Example: ...read more
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Q4. What are the differences between inner join and outer join in SQL?
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Inner join returns matching rows from both tables, while outer join returns all rows from one or both tables, with nulls for non-matches.
• Inner Join: Combines rows from two tables where there is a match based on a specified condition.

• Example: SELECT * FROM TableA INNER JOIN TableB ON TableA.id = TableB.a_id;

• Outer Join: Returns all rows from one table and matched rows from the other, filling with nulls where there is no ...read more
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Q5. What is the query to retrieve the 7th highest salary from the employee table for those with the designation of Software Developer?
Ans. 
To retrieve the 7th highest salary of Software Developers, use a SQL query with ranking functions or subqueries.
• Using Subquery: SELECT MAX(salary) FROM employees WHERE designation = 'Software Developer' AND salary < (SELECT DISTINCT salary FROM employees WHERE designation = 'Software Developer' ORDER BY salary DESC LIMIT 6);

• Using CTE: WITH RankedSalaries AS (SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS...read more
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Q6. What are the main components or building blocks of Object-Oriented Programming (OOP) in Java?
Ans. 
OOP in Java is based on four main principles: encapsulation, inheritance, polymorphism, and abstraction.
• Encapsulation: Bundling data and methods that operate on the data within one unit (class). Example: private variables with public getters/setters.

• Inheritance: Mechanism to create a new class using properties and methods of an existing class. Example: class Dog extends Animal.

• Polymorphism: Ability to present the same ...read more
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Q7. What is transaction management in JDBC, how is it handled, and what is the corresponding code?
Ans. 
Transaction management in JDBC ensures data integrity by grouping multiple operations into a single unit of work.
• Atomicity: Transactions ensure that all operations within a transaction are completed successfully or none at all, maintaining data integrity.

• Isolation: Transactions are isolated from each other, preventing concurrent transactions from interfering with one another.

• Consistency: Transactions bring the database...read more
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Q8. What is construction in Java, and what is its purpose?
Ans. 
Construction in Java refers to the process of creating objects using constructors, which initialize object attributes.
• Definition: A constructor is a special method invoked when an object is created, used to initialize the object's state.

• Types of Constructors: There are two types - default constructors (no parameters) and parameterized constructors (with parameters).

• Example of Default Constructor: public class Dog { Dog...read more
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Q9. What is the purpose of using the synchronized keyword in Java?
Ans. 
The synchronized keyword in Java ensures that a method or block is accessed by only one thread at a time, preventing concurrency issues.
• Used to control access to a method or block by multiple threads.

• Prevents thread interference and memory consistency errors.

• Example: synchronized void methodName() { // code }

• Can be applied to methods or blocks: synchronized(this) { // code }

• Only one thread can execute a synchronized me...read more
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Q10. What is serialization and deserialization, and how are these concepts used in Java?
Ans. 
Serialization is converting an object to a byte stream; deserialization is the reverse process in Java.
• Serialization allows Java objects to be saved to a file or sent over a network.

• In Java, classes must implement the Serializable interface to be serialized.

• Example: ObjectOutputStream can be used to serialize an object to a file.

• Deserialization is done using ObjectInputStream to recreate the object from the byte stream...read more
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Q11. What is the difference between method overloading and method overriding? Please provide examples.
Ans. 
Method overloading allows multiple methods with the same name but different parameters; overriding replaces a method in a subclass.
• Method Overloading: Same method name, different parameters (e.g., `add(int a, int b)` and `add(double a, double b)`)

• Method Overriding: Same method name and parameters in subclass (e.g., `class Animal { void sound() { } }` and `class Dog extends Animal { void sound() { } }`)

• Overloading is re...read more
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Q12. What is the sequence of execution for the start() and run() methods, and what is the purpose of the yield() method?
Ans. 
The start() method initiates a new thread, while run() contains the code executed by that thread. Yield() suggests thread scheduling.
• start() creates a new thread and invokes the run() method in that thread.

• run() contains the code that will be executed by the thread.

• yield() is a static method that hints the thread scheduler to pause the current thread and allow others to execute.

• Example: Calling thread1.start() will exe...read more
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Q13. What is the process for creating a thread-safe object?
Ans. 
Creating a thread-safe object involves ensuring that shared data is accessed safely by multiple threads.
• Use synchronization mechanisms like locks (e.g., Mutex in C++, synchronized in Java). Example: 'synchronized void method() { ... }'

• Utilize concurrent data structures (e.g., ConcurrentHashMap in Java) that handle synchronization internally.

• Implement immutability where possible, as immutable objects are inherently thre...read more
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Q14. What is the process for creating a singleton object?
Ans. 
A singleton ensures a class has only one instance and provides a global point of access to it.
• Define a private constructor to prevent instantiation from outside the class.

• Create a static variable to hold the single instance of the class.

• Provide a public static method to access the instance, creating it if it doesn't exist.

• Example in Java: public class Singleton { private static Singleton instance; private Sing...read more
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Q15. What is the difference between the List interface and the Map interface in Java?
Ans. 
The List interface stores ordered collections of elements, while the Map interface stores key-value pairs for efficient data retrieval.
• Data Structure: List is a collection of elements (e.g., ArrayList, LinkedList), while Map is a collection of key-value pairs (e.g., HashMap, TreeMap).

• Ordering: Lists maintain the order of elements based on insertion, whereas Maps do not guarantee any specific order unless using a specif...read more
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Q16. What is the difference between Integrator and ListIntegrator in Java?
Ans. 
Integrator and ListIntegrator are interfaces in Java for handling integration tasks, with ListIntegrator managing collections of integrators.
• Integrator: This interface is used for integrating a single function over a specified interval, typically returning a single result.

• ListIntegrator: This interface extends Integrator to handle a list of integrators, allowing for batch processing of multiple integration tasks.

• Exampl...read more
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Q17. What are the uses of the Map interface in Java?
Ans. 
The Map interface in Java is used to store key-value pairs, allowing efficient data retrieval and manipulation.
• 1. Key-Value Storage: Maps store data in pairs, where each key is unique. Example: Map<String, Integer> map = new HashMap<>();

• 2. Fast Lookups: Maps provide O(1) average time complexity for retrieval operations. Example: map.get('key');

• 3. Iteration: You can iterate over keys, values, or entries. Exa...read more
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Q18. What is the process for establishing a connection and inserting data into an Oracle database from a Java application?
Ans. 
Establishing a connection to an Oracle database in Java involves using JDBC for data insertion and management.
• JDBC Driver: Use the Oracle JDBC driver (ojdbc8.jar) to connect to the database. Example: Class.forName('oracle.jdbc.driver.OracleDriver');

• Connection String: Create a connection using DriverManager. Example: Connection conn = DriverManager.getConnection('jdbc:oracle:thin:@localhost:1521:xe', 'username', 'passwo...read more
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Q19. What is the difference between configuration parameters and context parameters in servlets?
Ans. 
Configuration parameters are set at deployment, while context parameters are specific to the servlet's runtime environment.
• Configuration Parameters: These are defined in the web.xml file and are used to configure the entire web application.

• Example: <context-param> in web.xml can define a database connection string.

• Context Parameters: These are specific to a servlet and can be accessed via the ServletContext.

• Examp...read more
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Q20. What is the difference between the forward method and the redirect method?
Ans. 
The forward method processes a request internally, while the redirect method sends a new request to a different URL.
• Forward Method: It forwards the request from one servlet to another within the same server, maintaining the original request and response objects.

• Example of Forward: In a Java servlet, using request.getRequestDispatcher('/newPage').forward(request, response) keeps the URL unchanged.

• Redirect Method: It sen...read more
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Q21. What are the various processes for handling session tracking in Servlets?
Ans. 
Session tracking in Servlets is crucial for maintaining user state across multiple requests in web applications.
• Cookies: Servlets can use cookies to store session identifiers on the client side, allowing the server to recognize returning users. Example: `Cookie sessionCookie = new Cookie("JSESSIONID", sessionId);`

• URL Rewriting: If cookies are disabled, session IDs can be appended to URLs. Example: `response.sendRedirec...read more
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Q22. What is the purpose of a Servlet filter?
Ans. 
Servlet filters are used to intercept requests and responses in a web application for processing tasks like logging and authentication.
• Filters can modify request and response objects before they reach the servlet or after the servlet processes them.

• Common use cases include logging request data, authentication, input validation, and response compression.

• For example, a logging filter can log the details of incoming reque...read more
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Q23. What is the difference between the generic service method and the doXxx() method in servlets?
Ans. 
Generic service methods handle requests generically, while doXxx() methods are specific to HTTP methods in servlets.
• Generic Service Method: This method can handle multiple types of requests (GET, POST, etc.) and is defined in the HttpServlet class.

• doGet() Method: Specifically handles HTTP GET requests, typically used for retrieving data from the server.

• doPost() Method: Specifically handles HTTP POST requests, used for ...read more
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Q24. What is encapsulation, and what are its uses?
Ans. 
Encapsulation is an object-oriented programming principle that restricts access to certain components of an object.
• Encapsulation helps in data hiding, preventing unauthorized access to sensitive data.

• It allows for controlled access through public methods (getters and setters).

• Example: A class 'BankAccount' can have private fields like 'balance' and public methods to deposit or withdraw money.

• Encapsulation enhances code...read more
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Q25. Difference between equals() and == operators?
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The '==' operator checks reference equality, while 'equals()' checks value equality in Java.
• '==' compares memory addresses for reference types.

• '==' checks for primitive types' actual values.

• 'equals()' is used to compare the contents of objects.

• Example: String a = new String('test'); String b = new String('test'); a == b // false, a.equals(b) // true
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Easy to medium aptitude questions you can expect

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