10+ Mayfair Housing Interview Questions and Answers

Immutable objects are those whose state cannot be changed after creation.

• Use final keyword to make class immutable

• Make all fields private and final

• Do not provide setter methods

• If a field is mutable, return a copy of it instead of the original object

• Examples: String, Integer, LocalDate

Singleton is a design pattern that restricts the instantiation of a class to one object.

• To create a singleton class, make the constructor private, create a static method to get the instance of the class, and create a private static variable to hold the instance.

• Benefits of singleton include ensuring only one instance of the class exists, providing a global point of access to the instance, and reducing the number of objects created in the system.

• Example: java.lang.Runtime is a...read more

Volatile is a keyword in Java used to indicate that a variable's value may be modified by multiple threads.

• Volatile variables are not cached in thread's local memory

• Changes made to volatile variables are immediately visible to other threads

• Volatile keyword is used to ensure visibility and ordering of variables in multithreaded environment

• Example: volatile int count = 0;

The @Component annotation is used to mark a class as a bean, while @Configuration is used to define a configuration class.

• The @Component annotation is used to auto-detect and auto-configure beans using classpath scanning.

• @Configuration classes are used to define beans and their dependencies explicitly.

• A @Configuration class can contain @Bean methods that return bean instances.

• A @Component class can be used as a bean in a Spring application context.

A program to create custom exceptions in Java.

• Create a class that extends Exception or RuntimeException

• Add constructors to the custom exception class

• Throw the custom exception in the code when needed

Microservices communicate through lightweight protocols like HTTP/REST or messaging systems like RabbitMQ.

• Microservices can communicate through synchronous protocols like HTTP/REST, where one service sends a request to another service and waits for a response.

• Microservices can also communicate through asynchronous messaging systems like RabbitMQ, where one service publishes a message to a queue and other services consume the message when they are ready.

• Microservices can use l...read more

To count duplicate names in SQL, use the GROUP BY clause with the COUNT function.

• Use GROUP BY clause to group the names together

• Use COUNT function to count the number of occurrences

• Use HAVING clause to filter out names with count less than 2

Java 1.8 introduced lambda expressions, default methods, and functional interfaces.

• Lambda expressions allow functional programming in Java.

• Default methods allow adding new methods to interfaces without breaking existing implementations.

• Functional interfaces are interfaces with a single abstract method, used for lambda expressions.

• Stream API for processing collections and arrays.

• Date and Time API for easier handling of date and time.

• Nashorn JavaScript engine for embedding Java...read more

Primary key uniquely identifies each record in a table, while unique key ensures that each value in a column is unique.

• Primary key does not allow NULL values, while unique key allows one NULL value.

• A table can have only one primary key, but multiple unique keys.

• Primary key automatically creates a unique index, while unique key does not.

• Primary key is used to establish relationships between tables, while unique key is used to enforce data integrity.

Securing a firewall involves configuring access control, implementing intrusion detection systems, and regularly updating security policies.

• Configure access control lists to allow only necessary traffic

• Implement intrusion detection systems to monitor for suspicious activity

• Regularly update firewall rules and security policies to address new threats

• Enable logging and monitoring to track firewall activity

• Use strong authentication methods for accessing the firewall

• Regularly revi...read more