Mjunction Services Java Developer Interview Questions and Answers

Q1. Explain Spring Boot
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Q2. What is Redux in React
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Q3. What is Context API in React
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Q1. They asked some core Java Concepts,String,Java 8,SpringBoot Architecture,Stream API code
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Q1. Difference between ArrayList and LinkedList?
Ans. 
ArrayList is implemented as a resizable array, while LinkedList is implemented as a doubly linked list.
• ArrayList provides fast random access, LinkedList provides fast insertion and deletion.

• ArrayList uses more memory as it needs to allocate a fixed size array, LinkedList uses more memory for storing references to the next and previous elements.

• Example: ArrayList is better for scenarios where random access is required, ...read more
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Q2. Difference between HashMap and HashTable?
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HashMap is non-synchronized and allows null values, while HashTable is synchronized and does not allow null values.
• HashMap is non-synchronized, meaning it is not thread-safe, while HashTable is synchronized and thread-safe.

• HashMap allows null values for both keys and values, while HashTable does not allow null keys or values.

• HashMap is faster than HashTable as it is non-synchronized, but HashTable is preferred in multi...read more
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Q1. What is the contract between hashCode and equals method?
Ans. 
The contract between hashCode and equals method is that if two objects are equal according to the equals method, then their hash codes must also be equal.
• hashCode and equals method must be consistent - if two objects are equal according to equals method, their hash codes must be equal

• If two objects have the same hash code, they may or may not be equal according to equals method

• Overriding equals method in a class requir...read more
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Q2. Features introduced in Java 8
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Java 8 introduced several new features including lambda expressions, functional interfaces, streams, and default methods in interfaces.
• Lambda expressions allow you to pass functions as arguments.

• Functional interfaces have a single abstract method and can be used with lambda expressions.

• Streams provide a way to work with sequences of elements.

• Default methods allow interfaces to have method implementations.
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Q3. What are the ways to start a thread
Ans. 
Ways to start a thread in Java
• Extending the Thread class and overriding the run() method

• Implementing the Runnable interface and passing it to a Thread object

• Using a thread pool from the Executors class
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Q4. What will happen if you start a thread which is already running
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The thread will continue running as it is already active
• The thread will not be started again if it is already running

• Attempting to start a thread that is already running will not have any effect

• The thread will continue its execution without any interruption
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Q5. Explain about the join and sleep method
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Join method is used to wait for a thread to finish its execution, while sleep method is used to pause the execution of a thread for a specified amount of time.
• Join method is used to wait for a thread to finish its execution before moving on to the next task.

• Sleep method is used to pause the execution of a thread for a specified amount of time, allowing other threads to run.

• Example: thread1.join() will wait for thread1 ...read more
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Q1. Micro service disadvantage
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Microservices can introduce complexity, communication overhead, and potential performance issues.
• Increased complexity due to managing multiple services

• Communication overhead between services

• Potential performance issues due to network latency

• Difficulty in maintaining consistency across services
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Q2. @functionalinterface can we extend or not, map & flatmap
Ans. 
No, @FunctionalInterface cannot be extended. Map and flatMap are default methods in the interface and cannot be overridden.
• No, @FunctionalInterface cannot be extended as it is a single abstract method interface.

• Map and flatMap are default methods in the interface and cannot be overridden.

• Example: public interface MyInterface { void myMethod(); default void myDefaultMethod() { // implementation } }
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Q1. Java8 coding to filter the vowels
Ans. 
Using Java8 to filter vowels from an array of strings
• Use Java8 stream and filter to iterate through each string in the array

• Use a lambda expression to check if each character is a vowel

• Collect the filtered strings into a new array
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Q2. Java8, Multi Threading, Hibernate, JPA
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30 multiple choice questions

Two coding questions

Q1. Oops questions like main principles of oops
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Q1. Deep in project
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Q1. Self intro, family background,some hr questions
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Q1. Explain OOPs concepts.
Ans. 
OOPs concepts are fundamental principles of object-oriented programming that help in designing and implementing software solutions.
• Encapsulation: Bundling data and methods together in a class.

• Inheritance: Creating new classes by inheriting properties and behaviors from existing classes.

• Polymorphism: Ability of an object to take on many forms.

• Abstraction: Hiding complex implementation details and providing a simplified ...read more
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Q2. Write a program to count occurance the letter in a string.
Ans. 
This program counts the occurrence of each letter in a given string.
• Use a HashMap to store the count of each letter.

• Iterate through the characters of the string and update the count in the HashMap.

• Finally, print the count of each letter.
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Q3. Write a SQL query to find third highest salary from employee table.
Ans. 
SQL query to find third highest salary from employee table.
• Use the ORDER BY clause to sort the salaries in descending order

• Use the LIMIT clause to limit the result to the third row

• Use a subquery to exclude the highest and second highest salaries
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Q4. Difference between Array and arraylist.
Ans. 
Array is a fixed-size data structure while ArrayList is a dynamic-size data structure in Java.
• Array has a fixed length, while ArrayList can grow dynamically.

• Array can store both primitive types and objects, while ArrayList can only store objects.

• Array uses square brackets [] for declaration, while ArrayList uses angle brackets <>.

• Array provides direct access to elements using index, while ArrayList provides methods for...read more
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Q5. Explain working of Arraylist.
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ArrayList is a dynamic array that can grow or shrink in size. It stores objects and provides methods for adding, removing, and accessing elements.
• ArrayList is part of the Java Collections Framework.

• It is implemented as a resizable array.

• Elements can be added using the add() method.

• Elements can be accessed using the get() method.

• Elements can be removed using the remove() method.

• The size() method returns the number of el...read more
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Q6. What is the default size of an arraylist.
Ans. 
The default size of an ArrayList is 10.
• The default initial capacity of an ArrayList is 10.

• If the number of elements exceeds the initial capacity, the ArrayList automatically increases its size.

• The capacity of an ArrayList can be increased manually using the ensureCapacity() method.
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Q7. Some questions from my resume about my previous experience.
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Q8. The interviewer was stupid and in my opinion they are just wasting your precious time. After the interview they don't provide any updates about the interview.
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