Core Java Most Commonly Asked Interview Questions.

• What are the differences between JDK, JRE, JVM, JIT?

• Which JDK version you used in your project?

• What are the Java 5, 7, 8 features?

• How to migrate the java 7 project to java 8 version?

• How to write Documentation Comment?

• What is Class & Object?

• What is OOPS and what are their pillars?What is Abstraction, Polymorphism, Inheritance and Encapsulation?

• How did you implemented OOPS concept in your project?

• What is static in java?

• What is final in java?

• Why can't a local variable have default value?

• What is Constructor and what are the differences between Constructor and Method?

• What is Constructor Chaining in Java?

• What are the things happening internally at memory level when we create an object in java? Explain Object creation steps.

• What is Static Polymorphism or Compile Time Polymorphism or Overloading or Early binding?

• What is Dynamic Polymorphism or Run Time Polymorphism or Overriding or Late Binding?

• What are the differences between Overloading and Overriding?

• Can we have different return type in overloading/overriding?

• Can we override static method ? Justify for YES or NO.

• How to restrict the methods from overriding?

• What are the difference between Interface and Abstract Class?

• Why Abstract Classes are there in Java?

• What is static import?

• What is path, classpath? What are the differences between them? How to set the path and classpath?

• What is jar-war-ear? Differences among them? How to create them? How to execute them?

• What is Diamond problem in Multiple Interitance?

• What is Has-A and Is-A relationship in java?

• Difference between Association vs Inheritance and Aggregation vs Composition.

• What is Coupling and Cohesion?

• What are the importance of Inner class in java, why did vendors design it?

• What is hashcode?

• Difference between equals method and == operator?

• What is cloning, Types of cloning,Difference between them Write the code to implement Deep Clone?

• What is garbage collection in java, Explain in detail.

• What are the differences between String, StringBuilder & StringBuffer?

• What is the difference between creating the string object with new operator and without new operator?

• What is String Constant Pool and Why String uses it?

• Why String is final, Immutable?

• Name the five important methods of String that you used so frequently.

• What is Auto - Boxing & Auto - Unboxing?
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• What are BigInteger and BigDecimal classes in java? 

• What are the differences among Heap, Stack and Method Area?

• What is design pattern?

• How to create singleton design pattern?

• What is Immutable Class and how to design Immutable class?

• How to break the singleton design pattern?

• What is class loader, How many types of class loaders are available in java?

• In how many ways we can create the object of class?

• What is difference between Compile Time and Runtime Exception?

• How to create user defined exception?

• What are the differences between final, finally & finalize?

• What are the differences between throw & throws?

• Which is  preferable between finally block and finalize method and why?

• Explain the Exception throwing rules while overriding the methods.

• In how many ways we can create the thread? Which one is preferable and why?

• Explain the thread life cycle.

• What are the differences between Sleep method and Wait method?

• Why wait and notify methods are available in Object class while being used in context of Thread Class?

• What is Synchronization? In how many ways we can apply Synchronization?Explain in detail.

• What is Deadlock? write the code for Deadlock.

• What is Consumer & Producer Problem? Write the code for the same. 

• What is thread pooling? explain it with codes?

• What is join method?Write the code to explain.

• What is Daemon Thread? How to create Daemon Thread?

• What is difference between stop & yield method in java?

• What is volatile keyword in java?

• What is collection? Draw the hierarchy of collection.

• What are the differences between Collection, Collection Framework & Collections?

• Which collection you used in your project and why?

• How does Set collection rejects the duplicate elements?

• What are the differences between:

•    Array vs ArrayList.             
•    ArrayList vs LinkedList.
•    List vs Set.
•    HashSet vs TreeSet.
•    Iterator vs ListIterator.
•    Comparable vs Comparator.

• What is Hashing Technique, How to avoid Collision in Hashing?

• Explain the internal Implementation of HashMap & LinkedHashMap?

• What are the differences between peak & poll of Queue?

• What is Concurrent Collection?

• What is Generic?

• What is Serialization? What is Transient? Can we serialize static variable?

• What is Reflection?

• What are the differences between creating the object using  newInstance method  and new operator?

Coding Round.

• Prime Number Checking.

• One Sorting Code.
• Second Highest Number.

• Star Pattern Printing Program.

• Factorial.

• Reverse String.

• Reverse Number.

• Count the occurrence of each character in given string.

• Consumer Producer Code.

• Dead Lock Code.
• Palindrome.
• Armstrong.
• Creation of Thread Pool.
• Temperature Conversion.

Various Company's Interview Questions Link below.

• Zensar 

• Ibm

• Mphasis

• Happiest Mind

• bridgei2i

• Mobily

• Ericsson

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