If you lot are preparing for your side past times side Core Java interview as well as looking for approximately mutual enquiry to practise or cheque your knowledge, as well as thence you lot accept come upwardly to the correct place. In this article, I'll portion 50 Core Java Interview Questions from diverse companies. I accept already discussed the answers to these questions inwards this spider web log or Javarevisited, thence I accept only set the link. First, you lot should endeavour to respond it yourself as well as if you lot cannot as well as thence acquire to the link as well as bring out the answer. You tin too compare your respond amongst mine as well as larn a few things hither as well as there. In most of my interview post, I accept too shared approximately mutual techniques to drive interview towards your comfort zone as well as how to acquire out a long-lasting impression on the interviewer, you lot tin work those techniques to do good on your Java interviews.
These questions are useful for both freshers as well as experienced Java programmers, mostly 2 to v years of experience. It too covers all of import topics for centre Java interviews, e.g. Java Fundamentals, Java Collections Framework, Java Multithreading as well as Concurrency, Serialization, Design Patterns, as well as JVM as well as Classloading.
1) How Java achieves platform independence? (answer)
hint: bytecode as well as Java Virtual Machine
2) What is ClassLoader inwards Java? (answer)
Hint: operate of JVM which loads bytecodes for classes. You tin write your own.
3) Write a Java computer program to cheque if a publish is Even or Odd? (answer)
hint: you lot tin work bitwise operator, e.g. bitwise AND &, remember, fifty-fifty publish has nix at the terminate inwards binary format, as well as an strange publish has 1 inwards the end.
4) Difference betwixt ArrayList as well as HashSet inwards Java? (answer)
hint: all differences betwixt List as well as Set are applicable here, e.g. ordering, duplicates, random search, etc.
5) What is double-checked locking inwards Singleton? (answer)
hint: two-time cheque whether instances is initialized or not, commencement without locking as well as instant amongst locking.
6) How do you lot do thread-safe Singleton inwards Java? (answer)
hint: many ways, e.g. using Enum or past times using double-checked locking designing or using nested static class.
7) When to work a volatile variable inwards Java? (answer)
hint: when you lot ask to learn JVM that a variable tin live modified past times multiple threads as well as give a hint to JVM that does non cache its value.
8) When to work a transient variable inwards Java? (answer)
Hint: when you lot desire to brand a variable non-serializable inwards a shape which implements the Serializable interface. In other words, you lot tin work it for a variable whose value you lot don't desire to save.
9) Difference betwixt the transient as well as volatile variable inwards Java? (answer)
hint: totally different, i used inwards the context of serialization acre other is used inwards concurrency.
10) Difference betwixt Serializable as well as Externalizable inwards Java? (answer)
hint: Externalizable gives you lot to a greater extent than command over the Serialization process.
11) Can nosotros override the someone method inwards Java? (answer)
hint: No, because it's non visible inwards the subclass, a principal requirement for overriding a method inwards Java.
answer)
Hint: several but most of import is Hashtable is synchronized acre HashMap is not. It's too legacy as well as irksome equally compared to HashMap.
13) Difference betwixt List as well as Set inwards Java? (answer)
hint: List is ordered as well as allows duplicate, Set is unordered as well as doesn't allow duplicate elements.
14) Difference betwixt ArrayList as well as Vector inwards Java (answer)
Hint: Many, but most of import is that ArrayList is non-synchronized as well as fast acre Vector is synchronized as well as slow. It's too legacy shape similar Hashtable.
15) Difference betwixt Hashtable as well as ConcurrentHashMap inwards Java? (answer)
hint: to a greater extent than scalable
16) How does ConcurrentHashMap attain scalability? (answer)
hint: past times dividing the map into segments as well as exclusively locking during the write operation. You tin farther see The Complete Java Masterclass to larn to a greater extent than almost how ConcurrentHashMap works.
17) Which ii methods you lot volition override for an Object to live used equally Key inwards HashMap? (answer)
hint: equals as well as hashcode
18) Difference betwixt hold back as well as slumber inwards Java? (answer)
hint: The wait() method releases the lock or monitor, acre slumber doesn't.
19) Difference betwixt notify as well as notifyAll inwards Java? (answer)
Hint: notify notifies i random thread is waiting for that lock acre notifyAll inform to all threads waiting for a monitor. If you lot are surely that exclusively i thread is waiting, as well as thence work notify, or else notifyAll is better.
20) Why you lot override hashcode, along amongst equals() inwards Java? (answer)
hint: to live compliant amongst equals as well as hashcode contract which is required if you lot are planning to shop your object into collection classes, e.g. HashMap or ArrayList.
21) What is the charge cistron of HashMap means? (answer)
hint: The threshold which triggers re-sizing of HashMap, by as well as large 0.75, which agency HashMap resize itself if it's 75% full.
22) Difference betwixt ArrayList as well as LinkedList inwards Java? (answer)
Hint: same equally an array as well as linked list, i allows random search acre other doesn't. Insertion as well as deletion piece of cake on the linked list, but a search is piece of cake on an array.
23) Difference betwixt CountDownLatch as well as CyclicBarrier inwards Java? (answer)
hint: You tin reuse CyclicBarrier after the barrier is broken, but you lot cannot reuse CountDownLatch after the count reaches to zero. You tin farther see Multithreading as well as Parallel Computing inwards Java course of written report on Udemy to larn to a greater extent than almost concurrency utility classes similar CyclicBarrier, Phaser, as well as CountDownLatch inwards Java.
24) When do you lot work Runnable vs. Thread inwards Java? (answer)
hint: always
25) What is the pregnant of Enum type-safe inwards Java? (answer)
Hint: It agency you lot cannot assign an representative of dissimilar Enum type to an Enum variable. e.g., if you lot accept a variable similar DayOfWeek day, as well as thence you lot cannot assign it value from DayOfMonth enum.
26) How does Autoboxing of Integer piece of work inwards Java? (answer)
hint: using valueOf() method
27) Difference betwixt PATH as well as Classpath inwards Java? (answer)
hint: PATH is used past times the operating arrangement acre Classpath is used past times JVM to locate Java binary, e.g. JAR files or Class files.
28) Difference betwixt method overloading as well as overriding inwards Java? (answer)
Hint: Overriding happens at subclass acre Overloading happens inwards the same class. Also, overriding is a runtime activeness acre overloading is resolved at compile time.
29) How do you lot preclude a shape from beingness sub-classed inwards Java? (answer)
hint: only brand its constructor private
30) How do you lot limit your shape from beingness used past times your client? (answer)
hint: brand the constructor someone or throw an exception from the constructor
31) Difference betwixt StringBuilder as well as StringBuffer inwards Java? (answer)
hint: StringBuilder is non synchronized acre StringBuffer is synchronized.
32) Difference betwixt Polymorphism as well as Inheritance inwards Java? (answer)
hint: Inheritance allows code reuse as well as builds the human relationship betwixt class, which is required past times Polymorphism, which provides dynamic behavior.
33) Can nosotros override static method inwards Java? (answer)
hint: No because overriding resolves at runtime acre static method telephone phone is resolved at compile time.
34) Can nosotros access the someone method inwards Java? (answer)
hint: yes, inwards the same shape but non exterior the class
35) Difference betwixt interface as well as abstract shape inwards Java? (answer)
hint: from Java 8, the divergence is blurred, but notwithstanding a Java shape tin implement multiple interfaces but tin extend only i class.
36) Difference betwixt DOM as well as SAX parser inwards Java? (answer)
Hint: DOM loads whole XML File inwards retention acre SAX doesn't. It is an event-based parser as well as tin live used to parse a large file, but DOM is fast as well as should live preferred for pocket-sized files.
37) Difference betwixt throw as well as throws keyword inwards Java? (answer)
hint: throws declare what exception a method tin throw inwards representative of mistake but throw keyword genuinely throws an exception.
38) Difference betwixt fail-safe as well as fail-fast iterators inwards Java? (answer)
hint: fail-safe doesn't throw ConcurrentModificationException acre fail-fast does whenever they honour as well as exterior modify on underlying collection acre iterating over it.
39) Difference betwixt Iterator as well as Enumeration inwards Java? (answer)
hint: Iterator too gives you lot the mightiness to take away an chemical ingredient acre iterating acre Enumeration doesn't allow that.
40) What is IdentityHashMap inwards Java? (answer)
hint: Influenza A virus subtype H5N1 Map which uses == equality operator to cheque equality instead of equals() method.
41) What is String puddle inwards Java? (answer)
Hint: Influenza A virus subtype H5N1 puddle of String literals. Remember it's moved to heap from perm gen infinite inwards JDK 7.
42) Can a Serializable shape comprise a non-serializable champaign inwards Java? (answer)
hint: Yes, but you lot ask to acquire far either static or transient.
43) Difference betwixt this as well as super inwards Java? (answer)
hint: this refers to the electrical flow representative acre super refers to an representative of the superclass.
44) Difference betwixt Comparator as well as Comparable inwards Java? (answer)
hint: Comparator defines custom ordering acre Comparable defines the natural lodge of objects, e.g. the alphabetic lodge for String.
45) Difference betwixt java.util.Date as well as java.sql.Date inwards Java? (answer)
hint: erstwhile contains both appointment as well as fourth dimension acre afterward contains exclusively appointment part.
46) Why hold back as well as notify method are declared inwards Object shape inwards Java? (answer)
hint: because they require lock which is exclusively available to an object.
47) Why Java doesn't back upwardly multiple inheritances? (answer)
Hint: It doesn't back upwardly because of a bad sense amongst C++, but amongst Java 8, it does inwards approximately sense. Only multiple inheritances of Type is non supported inwards Java now.
48) Difference betwixt Checked as well as Unchecked Exception inwards Java? (answer)
hint: In representative of checked, you lot must grip exception using grab block, acre inwards representative of unchecked, it's upwardly to you, compile volition non bother you.
49) Difference betwixt Error as well as Exception inwards Java? (answer)
hint: I am tired of typing, delight cheque the answer
50) Difference betwixt race status as well as deadlock inwards Java? (answer)
hint: both are errors occur inwards a concurrent application, i occurs because of thread scheduling acre others occur because of pitiable coding.
Resources
Java Interview Guide: 200+ Interview Questions as well as Answers
Spring Framework Interview Guide - 200+ Questions & Answers
Preparing For a Job Interview By John Sonmez
Java Programming Interview Exposed past times Markham
Cracking the Coding Interview - 189 Questions as well as Answers
Data Structure as well as Algorithms Analysis for Job Interviews
Thanks for reading this article thence far. If you lot similar these Core Java Questions, as well as thence delight portion amongst your friends as well as colleagues. If you lot accept whatever questions or feedback, as well as thence delight driblet a note.
These questions are useful for both freshers as well as experienced Java programmers, mostly 2 to v years of experience. It too covers all of import topics for centre Java interviews, e.g. Java Fundamentals, Java Collections Framework, Java Multithreading as well as Concurrency, Serialization, Design Patterns, as well as JVM as well as Classloading.
Core Java Interview Questions amongst Answers
Without whatever farther ado, hither is my listing of 50 Core Java Interview Questions amongst Answers equally a link:1) How Java achieves platform independence? (answer)
hint: bytecode as well as Java Virtual Machine
2) What is ClassLoader inwards Java? (answer)
Hint: operate of JVM which loads bytecodes for classes. You tin write your own.
3) Write a Java computer program to cheque if a publish is Even or Odd? (answer)
hint: you lot tin work bitwise operator, e.g. bitwise AND &, remember, fifty-fifty publish has nix at the terminate inwards binary format, as well as an strange publish has 1 inwards the end.
4) Difference betwixt ArrayList as well as HashSet inwards Java? (answer)
hint: all differences betwixt List as well as Set are applicable here, e.g. ordering, duplicates, random search, etc.
5) What is double-checked locking inwards Singleton? (answer)
hint: two-time cheque whether instances is initialized or not, commencement without locking as well as instant amongst locking.
6) How do you lot do thread-safe Singleton inwards Java? (answer)
hint: many ways, e.g. using Enum or past times using double-checked locking designing or using nested static class.
7) When to work a volatile variable inwards Java? (answer)
hint: when you lot ask to learn JVM that a variable tin live modified past times multiple threads as well as give a hint to JVM that does non cache its value.
8) When to work a transient variable inwards Java? (answer)
Hint: when you lot desire to brand a variable non-serializable inwards a shape which implements the Serializable interface. In other words, you lot tin work it for a variable whose value you lot don't desire to save.
9) Difference betwixt the transient as well as volatile variable inwards Java? (answer)
hint: totally different, i used inwards the context of serialization acre other is used inwards concurrency.
10) Difference betwixt Serializable as well as Externalizable inwards Java? (answer)
hint: Externalizable gives you lot to a greater extent than command over the Serialization process.
11) Can nosotros override the someone method inwards Java? (answer)
hint: No, because it's non visible inwards the subclass, a principal requirement for overriding a method inwards Java.
Hint: several but most of import is Hashtable is synchronized acre HashMap is not. It's too legacy as well as irksome equally compared to HashMap.
13) Difference betwixt List as well as Set inwards Java? (answer)
hint: List is ordered as well as allows duplicate, Set is unordered as well as doesn't allow duplicate elements.
14) Difference betwixt ArrayList as well as Vector inwards Java (answer)
Hint: Many, but most of import is that ArrayList is non-synchronized as well as fast acre Vector is synchronized as well as slow. It's too legacy shape similar Hashtable.
15) Difference betwixt Hashtable as well as ConcurrentHashMap inwards Java? (answer)
hint: to a greater extent than scalable
16) How does ConcurrentHashMap attain scalability? (answer)
hint: past times dividing the map into segments as well as exclusively locking during the write operation. You tin farther see The Complete Java Masterclass to larn to a greater extent than almost how ConcurrentHashMap works.
17) Which ii methods you lot volition override for an Object to live used equally Key inwards HashMap? (answer)
hint: equals as well as hashcode
18) Difference betwixt hold back as well as slumber inwards Java? (answer)
hint: The wait() method releases the lock or monitor, acre slumber doesn't.
19) Difference betwixt notify as well as notifyAll inwards Java? (answer)
Hint: notify notifies i random thread is waiting for that lock acre notifyAll inform to all threads waiting for a monitor. If you lot are surely that exclusively i thread is waiting, as well as thence work notify, or else notifyAll is better.
20) Why you lot override hashcode, along amongst equals() inwards Java? (answer)
hint: to live compliant amongst equals as well as hashcode contract which is required if you lot are planning to shop your object into collection classes, e.g. HashMap or ArrayList.
21) What is the charge cistron of HashMap means? (answer)
hint: The threshold which triggers re-sizing of HashMap, by as well as large 0.75, which agency HashMap resize itself if it's 75% full.
22) Difference betwixt ArrayList as well as LinkedList inwards Java? (answer)
Hint: same equally an array as well as linked list, i allows random search acre other doesn't. Insertion as well as deletion piece of cake on the linked list, but a search is piece of cake on an array.
23) Difference betwixt CountDownLatch as well as CyclicBarrier inwards Java? (answer)
hint: You tin reuse CyclicBarrier after the barrier is broken, but you lot cannot reuse CountDownLatch after the count reaches to zero. You tin farther see Multithreading as well as Parallel Computing inwards Java course of written report on Udemy to larn to a greater extent than almost concurrency utility classes similar CyclicBarrier, Phaser, as well as CountDownLatch inwards Java.
24) When do you lot work Runnable vs. Thread inwards Java? (answer)
hint: always
25) What is the pregnant of Enum type-safe inwards Java? (answer)
Hint: It agency you lot cannot assign an representative of dissimilar Enum type to an Enum variable. e.g., if you lot accept a variable similar DayOfWeek day, as well as thence you lot cannot assign it value from DayOfMonth enum.
26) How does Autoboxing of Integer piece of work inwards Java? (answer)
hint: using valueOf() method
27) Difference betwixt PATH as well as Classpath inwards Java? (answer)
hint: PATH is used past times the operating arrangement acre Classpath is used past times JVM to locate Java binary, e.g. JAR files or Class files.
28) Difference betwixt method overloading as well as overriding inwards Java? (answer)
Hint: Overriding happens at subclass acre Overloading happens inwards the same class. Also, overriding is a runtime activeness acre overloading is resolved at compile time.
29) How do you lot preclude a shape from beingness sub-classed inwards Java? (answer)
hint: only brand its constructor private
30) How do you lot limit your shape from beingness used past times your client? (answer)
hint: brand the constructor someone or throw an exception from the constructor
hint: StringBuilder is non synchronized acre StringBuffer is synchronized.
hint: Inheritance allows code reuse as well as builds the human relationship betwixt class, which is required past times Polymorphism, which provides dynamic behavior.
hint: No because overriding resolves at runtime acre static method telephone phone is resolved at compile time.
hint: yes, inwards the same shape but non exterior the class
hint: from Java 8, the divergence is blurred, but notwithstanding a Java shape tin implement multiple interfaces but tin extend only i class.
36) Difference betwixt DOM as well as SAX parser inwards Java? (answer)
Hint: DOM loads whole XML File inwards retention acre SAX doesn't. It is an event-based parser as well as tin live used to parse a large file, but DOM is fast as well as should live preferred for pocket-sized files.
hint: throws declare what exception a method tin throw inwards representative of mistake but throw keyword genuinely throws an exception.
hint: fail-safe doesn't throw ConcurrentModificationException acre fail-fast does whenever they honour as well as exterior modify on underlying collection acre iterating over it.
hint: Iterator too gives you lot the mightiness to take away an chemical ingredient acre iterating acre Enumeration doesn't allow that.
hint: Influenza A virus subtype H5N1 Map which uses == equality operator to cheque equality instead of equals() method.
Hint: Influenza A virus subtype H5N1 puddle of String literals. Remember it's moved to heap from perm gen infinite inwards JDK 7.
hint: Yes, but you lot ask to acquire far either static or transient.
hint: this refers to the electrical flow representative acre super refers to an representative of the superclass.
hint: Comparator defines custom ordering acre Comparable defines the natural lodge of objects, e.g. the alphabetic lodge for String.
hint: erstwhile contains both appointment as well as fourth dimension acre afterward contains exclusively appointment part.
hint: because they require lock which is exclusively available to an object.
Hint: It doesn't back upwardly because of a bad sense amongst C++, but amongst Java 8, it does inwards approximately sense. Only multiple inheritances of Type is non supported inwards Java now.
hint: In representative of checked, you lot must grip exception using grab block, acre inwards representative of unchecked, it's upwardly to you, compile volition non bother you.
hint: I am tired of typing, delight cheque the answer
hint: both are errors occur inwards a concurrent application, i occurs because of thread scheduling acre others occur because of pitiable coding.
Resources
Java Interview Guide: 200+ Interview Questions as well as Answers
Spring Framework Interview Guide - 200+ Questions & Answers
Preparing For a Job Interview By John Sonmez
Java Programming Interview Exposed past times Markham
Cracking the Coding Interview - 189 Questions as well as Answers
Data Structure as well as Algorithms Analysis for Job Interviews
Thanks for reading this article thence far. If you lot similar these Core Java Questions, as well as thence delight portion amongst your friends as well as colleagues. If you lot accept whatever questions or feedback, as well as thence delight driblet a note.
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