Java Interview questions

Interview questions Java

1. What is Fail-Fast and Fail Safe Systems?
2. What is the difference between Encapsulation and Abstraction?
    There are two objects a and b with same hashcode. I am inserting these two objects inside a hashmap.
3. hMap.put(a,a);
   hMap.put(b,b);
4. where a.hashCode()==b.hashCode()
5. Now tell me how many objects will be there inside the hashmap?
6. What is the difference between StringBuffer and String class ?
7. What are Marker Interfaces ? Name few Java marker interfaces ?
8. What are various types of Class loaders used by JVM ?
9. What are RESTful Web Services ?
10. What is a cyclic dependency ?
11. What is reflection ?
12. How are classes loaded by JVM ?
13. What is the use of HashCode in objects ?
14. What is a ConcurrentHashMap ?
15. How is Hashmap internally implemented in Java ?
16. What is a Servlet Filter ?
17. What are the ways to get the values from list ?
18. There are 8 balls, 7 weigh 100 gms, 1 is defective, there is a weighing scale, any number of balls can be measured at the same time. in how many attempts defective balls can be found out.
19. 
    serialization and deserialization of singleton class
20. serialization and deserialization of singleton class
21. what is volatile and atomic
22. How many read and write operations are provided at the same time by ConcurrentHashMaps ?
23. 
    
    in the following class:
    class A {
    void methoda(Object o) {
    Sysout("Object");
    }
24. void methoda(String s) {
    
    Sysout("String");
    }
25. public static void main(String []args) {
    
    A a = new A();
    a.methoda(null);
    }
    }
26. what will be printed?
27. Explain Hibernate caching mechanism?
28. Explain the difference between JDK, JRE, and JVM.
29. What makes Java a platform-independent programming language?
30. Would it be correct to say that Java is not 100% Object-oriented?
31. What is a constructor in Java?
32. Differentiate between a constructor and a method? Can we mark constructors final?
33. What is a class in Java?
34. State the significance of public, private, protected class.
35. What is the final class?
36. What is a wrapper class?
37. What is an abstract class?
38. Describe synchronization with respect to multi-threading.
39. What is the purpose of garbage collection in Java, and when is it used?
40. What are the different ways of implementing thread? Which one is more advantageous?
41. What if the main() method is declared as private? What happens when the static modifier is removed from the signature of the main() method?
42. What is the first argument of the String array in main() method?
43. What is a Java servlet?
44. Describe the Life-cycle of a Java Servlet.
45. Explain the Request Dispatcher?
46. List the steps to connect to a database in java?
47. What do you mean by a JDBC Driver?
48. What is a Java applet?
49. What is a numeric promotion?
50. What is false sharing in the context of multi-threading?
51. What are the methods used to implement for the key Object in HashMap?
52. What is an immutable object?
53. Differentiate between String Buffer and String Builder in Java?
54. What is the difference between factory and abstract factory pattern?
55. Differentiate JAR and WAR files
56. What is a JIT compiler?
57. What is the multi-catch block in Java? 
58. What is Hashcode
59. What is callable interface
60. Where we use Hashcode?
61. Why Hashcode?
62. Explain types of design pattern
63. What is factory design pattern?
64. What is advantable of java serialization?
65. What is serial no of serialization why we require it ?
66. Can a static veriable be serialized?
67. Can a transient variable be serialiazed?
68. what is diamond problem
69. what is spring IOC and types
70. advantages of applicationcontext over beanfactory
71. design patterns
72. what is bean scopes and how global session scope works
73. what is singleton
74. lifecycle of a bean
75. spring security principal
76. spring cloud
77. rest vs soap
78. what  microservices and framework
79. JAX-RS annotations
80. spring annottaions
81. what is ORM and JPA
82. JPA annoations and how to access the data from table on the basis of columne name and order by using JPA
83. what is spring authrorization
84. oauth2.0 working
85. what is work of dispatcher servlet
86. what is work of view resolver
87. how to handle the exception in spring
88. if there are two @Controller advice in an application, then which one will be called - @Ordered
89. git commands
90. apache camel
91. ways to implement spring security
92. how to gain concurrency in spring
93. how to check health of rest service..
94. what is oops
95. oops concepts in java
1. set vs list
2. set vs map
3. treeset vs hashset
4. internal working of set
5. internal working of map
6. stream api vs old java nested for loops
7. polymorphism
8. design patterns
9. pizza problem- decorator vs builder pattern
10. spring conttext
11. spring scopes
12. fetch type in hibernate - https://www.mkyong.com/hibernate/hibernate-fetching-strategies-examples/
13. hashset vs hashtable
14. spring mvc
15. what is time complexity improvement in stream api of java
16. what is generic types
17. how stream api works and advantages of use
18. jenkins
19. maven
20. hashcode and equals method
21. program to count the frequency of char in a string
22. spring cloud
23. program to find the combination of no whose sum is 10 ()1,2,3,4,5,6,7,8,9)
24. how the microservices communicate with each others
25. what is microservices
26. what is DI and ways to do
27. when to use constructor based and setter based DI
28. what is IOC in spring
29. type of IOC
30. applicationcontext vs beanfactory
31. advantages of applicationcontext
32. difference between lazy and early inalization
33. IS A and HAS a realationship
34. aggregation, composition aand association
35. how index works
36. What is the return type of compareTo Method ? What is comparable interface?