10+ DR JOY DENTAL CLINIC DUBAI . UAE Interview Questions and Answers

Java interview questions on OOPS concepts, polymorphism, exceptions, data structures, and threading.

• OOPS concepts include encapsulation, inheritance, and polymorphism.

• Polymorphism refers to the ability of an object to take on multiple forms.

• Singleton class is a class that can only have one instance, while factory method is a method that creates objects.

• Exception is an error that occurs during program execution, with a hierarchy of exceptions.

• Volatile keyword is used to indica...read more

Implement a SQL query for given examples

• Use SELECT statement to retrieve data from tables

• Use WHERE clause to filter results based on conditions

• Use JOIN clause to combine data from multiple tables if needed

Filter out strings starting with 'a' and convert to uppercase using Streams

• Use Stream.filter() to filter out strings starting with 'a'

• Use Stream.map() to convert remaining strings to uppercase

• Collect the result back into an array using Collectors.toList()

Using Java 8 streams to count frequency of elements in an array of strings

• Use Java 8 streams to convert the array to a map with element as key and count as value

• Use Collectors.groupingBy and Collectors.counting to achieve this

• Example: Arrays.stream(array).collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))

HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.

• HashMap is implemented using an array of linked lists, where each element is a key-value pair stored in a Node object.

• When a key-value pair is added to the HashMap, the key is hashed to determine the index in the array where the pair will be stored.

• If multiple key-value pairs hash to the same index, they are stored in a linked list at that index.

• HashMap uses hashing to quic...read more

Interface defines a contract for classes to implement, while abstract class provides partial implementation.

• Interface can have only abstract methods, while abstract class can have both abstract and concrete methods.

• A class can implement multiple interfaces but can only extend one abstract class.

• Interfaces are used for achieving multiple inheritance in Java.

• Abstract classes are used when some common functionality needs to be shared among multiple classes.

Microservices design pattern is an architectural style that structures an application as a collection of loosely coupled services.

• Each service is responsible for a specific function and can be developed, deployed, and scaled independently.

• Communication between services is typically done through APIs, allowing for flexibility and resilience.

• Microservices promote agility, scalability, and maintainability in large and complex applications.

• Examples of companies using microservice...read more

Java 8 streams provide a way to process collections of objects in a functional style.

• Streams are created from collections using stream() method

• Operations like filter, map, reduce can be applied to streams

• Terminal operations like forEach, collect are used to process the stream

Multithreading allows multiple threads to execute concurrently within a single process.

• Multithreading improves performance by allowing tasks to run in parallel.

• Each thread has its own stack and shares the same heap memory.

• Java provides built-in support for multithreading through the Thread class and Runnable interface.

Merge two lists in Java

• Create a new list to store the merged result

• Use addAll() method to add elements from both lists to the new list

• Return the merged list