Java Interview questions

2. 1. Which one is efficient in terms of retrieval between TreeMap and HashMap
   2. What is an atomic operation and synchronized in Java?
   3. We have ReST Service and multiple clients accessing it. How do you handle the count of calls to ReST Service from these clients including concurrent calls
   4. We have Hive Tables - Emp Table and Dept Table and a join query to get employee name and department name on join condition empId == deptId. Can you explain internal execution of this hive query?
   5. Explain the mechanism of Mapper Output related to Reducers Input.
   6. What is the default partitioner used in Spark?
   7. How to handle data skew and cleansing operations?
   8. Do you know about Spark Execution Memory Model?
   9. Since you have 15+ yrs of exp, what type of role are you looking at (Non-Technical) 
3. 1. Explain purpose of Spring Profiles
   2. How do you find the middle node in a singly linked list without using any built-in functionality?
   3. When we try to place key-value pair with an already existing key into a hashmap, what happens? Explain the internal working of HashMap.
   4. HashMap already has an entry for (key1,10). If we try to place again with different value say (key1,20). What would be a value returned for map? get(key1) and why?
   5. How do you store passwords in Java? Which is preferred - String or CharacterArray?
   6. What is JPA/Hibernate?
   7. Write SQL Query to find the maximum salary for a department given dept_id and salary fields in department table
   8. What is the purpose of ZooKeeper in Kafka Cluster?
   9. How is load balancing achieved in Kafka while publishing messages to Kafka Brokers?
   10. In method overloading with xyz(Object o) and  xyz(String s), if we call XYZ(null), which the method gets called by the compiler and explain
   11. Explain what happens when you execute the Springboot Application 

   Can Kafka be used without ZooKeeper?

4. I have 10 GB file and how do process in java?
5. I have 10 files and want to run process these files in multithreading. how can you write code find the count of records processed at any given time?
6. what are the different connection pooling properties? consider in the situation how can you or application handle that record needs to updated to the database but not getting connection due to network failure.
7. i have two tables employee with empid, deptid, and department table with deptid, dept name and there are null values for deptid in the employee table. how you can write a query to retrieve all employee records with department name along with null dept id's
8. how will you read and write 5GB big data files from one file location to another location with less memory 512mb  in java?
9. what are an atomic integer and its usage?
10. How could we share the value between the multiple threads?
11. what is the use of post construct method in spring
12. Query to display emp id, dept id, and dept name if dept name is empty should display default  department name from two tables employee and department 
13. What is cursor in pl SQL
14. Any working knowledge of Hadoop and big data.
15. Explain the current project functionality and architecture 
16. how to make run threads in sequence  
17. what use are Atomic Variables in thread
18. what is the use of @autowired in spring what  internally happens
19. you have n number of threads how to run in sequence printing by each thread tell pseudo code
20. spring design patterns and explain
21. what are scopes in spring
22. what is the singleton bean
23. how to inject prototype bean into a singleton bean
24. Explain the spring application context
25. java 8 features and what is the use of Default method
26. what is the difference between the SQL and NoSQL databases
27. which scenario you use MongoDB and relational databases
28. what is docker has written any docker images
29. how fetch the data between the table write a query using joins with  table records are given
30. what use of NVLwhere it uses
31. how to find out if your facing issue product environment
32. angular and which version you used in developing applications and application flow
33. Find the middle of the LinkedList in the collection using a double linked node method.
34. What is the need to override the hashcode method in HashMap
35. Spring - life cycle of Bean
36. Multi-threading program - need to print the 1 to 100 based on the inputs like no of thread 
37. e.g - if no of a thread is 2 then, print the values like 123 from thread 1 and 456 from thread2.
38. SQL - find the second max salary of every dept in an employee table 
39. e.g employee table - empid, empname, deptid, salary 
40. Hibernate  eager loading and lazy loading difference
41. Multithreading synchronization method and normal method difference 
42. Spring batch  chunk () method use
43. Spring batch partition () method use
44. Multithreading four threads each thread is printing sequence numbers 1,2,3,4  and again same threads will continue the same, explain the step by step process.
45. Get and load method difference in hibernate 
46. What are the design patterns available in Microservice that are utilized in this project?  (Based on skillset added in specific profile)
47. What are the important features of JavaSE 8?
48.  Explain Java Lambda Expressions and advantages?
49.  Java Stream API and map, reduce concepts in stream methods (Scenario-based)? (In an ArrayList of 10 elements, we need to add like (1*1 +2*2....10*10) and need to execute the output greater than 64?).
50.  How the Multi-threading is handled using executors?
51.  What are the design patterns that are used in Spring Framework?
52.  What are the high-level architecture and internal structure of Spring?  (Not like, from the dispatcher to view mode).
53.  Explain IOC and its concepts used in Spring with advantages?
54.  Explain Spring AOP?  (Scenario-based)?
55.   How to write the query for getting the results which are greater than 30% marks, For Ex? (We want to retrieve specific information from a table excluding other irrelevant data)
56.  How to list all rows in a table whose column values match a specified pattern? (Search capabilities of a SQL query.)   
57.  Does the wild card search is case sensitive in SQL?  (Extends from the Question 11, Similar)
58. What is the ConcurrentHashMap in what it is different from Synchronized HashMap and HashMap
59. What is HashSet and when we use it?
60. When to use the ArrayList and LinkedList
61. What is the significance of equals and hashcode...what if either of these methods is not overloaded
62. What is Deadlock? Give an example or scenario. How to avoid the deadlocks
63. If want to build the screen to fetch the data from DB, how many days you require
64. What are the different classes we require to write for developing the screen
65. What is the AOP and how to configure using an example
66. What are Microservices and where you have used
67. What are the design patterns used in Microservices
68. How to configure OneToMany and ManyToOne mapping in hibernate
69. What is eager and lazy in hibernate
70. How to write the Joins, asked with an example scenario
71. What is JDBCTemplate and what is the internal design pattern implementation used here
72. What is the template method design pattern
73. What is a strategy design pattern
74. What is rowMapper and what is the internal design pattern used here
75. What are the used Java 8 features?
76. What is Lambda expression and how to define with an example
77. Does Lambda requires the functional interface or without functional interface also Lambda can be used?
78. What is the stream...How to use and what are the benefits...how to retrieve only odd a number from 1-100 using streams
79. What is the life cycle of thread and methods involved in it
80. How to print odd and even numbers sequentially using 2 threads
81. What are the design patterns you know?
82. What is the singleton design pattern?
83. How will you write a design patten to maintain only two objects?
84. What will you do to create a new object on every hit in Spring?
85. Have you worked in Thread concepts?
86. Brief about the last project?
87. why are you going for Docker and open shift?
88. Difference b/w stateful and stateless service?
89. Explain all OOPs concepts with real-time example?
90. What is Second level cache & first level cache?
91. What is IOC?
92. What is Linked HashSet and when to use?
93. What is the purpose of the framework? 
94. What is the time complexity of HashMap for searching? What are the algorithm and data structure used for this?
95. If two same data tables each having 3 rows...when performed an inner join, how many records it will fetch for you
96. If two same data tables each having 3 rows...when performed cross join, how many records it will fetch for you
98. Are you aware of Spring batch
99. Are you aware of PL/SQL
100. Explain how to print odd and even numbers sequentially using 2 threads
101. Internal working of Hashmap and it's time complexities.
102. Singleton design pattern and how to make it synchronized
103. Print odd-even with two threads.
104. How to create an immutable class.
105. Query to select all the records of employees and only the matching records of the department.
106. Query to select the max salary for every department.