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Core Java Interview Questions(Top Core Java Questions)


Hello Everyone, Here are some hot interview questions on core java. Go through it and get answer by yourself

Explain about JVM ? Explain about JRE ? What is mean by bytecode? Explain about System.out.println(” ……….”);  why we want.....




Here are some hot interview questions on core java. Go through it and get answer by yourself



1. Explain about JVM ?

2. Explain about JRE ?

3. What is mean by bytecode?Explain about System.out.println(” ……….”); 

4. why we want to use “System” ? and what is the “System”?Explain flow of java program execution?

5. Explain about JIT compilation?Explain JAVA features?

6. Why java is object oriented programming language?

7. What are the  principles of  OOPS?

8. What is an object, explain properties of an object ?

10. What is class? Explain Object class methods?

11. What is Encapsulation give me one example?

12. What is Abstraction give me one example?

13. What is mean by polymorphisms and types of polymorphism explain?

14. What is the difference between dynamic polymorphism and static polymorphism?

15. Explain Is-a & has-a relationship?

16. What is object life time?

17. What is inheritance and explain types of inheritance?

18. What is constructor?How many types of constructors are there and explain?

19. Can we call explicitly constructor?

20. How can we call from default constructor parameterized constructor?

21. Does a class inherit the constructor of its super class?

22. Can we make constructor static?

23. Can we make final keyword before constructor?

24. What is the difference between constructor and method?

25. What is hash code?Character default value?

26. Can you declare a class as private?When is a constructor called, before or after creating the object?What is the difference between default constructor and parameterized constructor?What is constructor over loading?Can we make access specifiers before constructor?What is mean by Access specifier and types of access specifier?Leas order of Access specifier?Heighest order of Access specifier?What is mean by access modifiers and explain?What is the difference between the instance variables and static variables?What are instance methods?What are static methods?Why instance variable not available to static methods?In how many ways can you create an object in java?What is anonymous inner class?What are factory methods?Is it possible to compile and run a java program without writing main method()?How objects are passed to methods in java?What is the use of this(),this(..) keywords?What is the use of super(),super(..) keywords?What is the difference between this() and super() keywords?Can we override private methods?Can we take private methods and final methods as same?What is final?How to prevent method overriding?How to prevent inheritance in java?What is mean by shadowing?Can we possible to override the static methods?What is static block and explain?What is instance block and explain?What is difference between instance block and static block?Incorporating more than one constructor in a class is called?What is specialization and generalization?What is implicit casting?What is explicit casting?Can we call class as a data type?What happens if main() method is written without String args[ ] ?Can you call the main() of a class from another class?What are the modifiers in java?What is abstract method?What is abstract class?Abstract classes can contain abstract methods?Explain about transient modifier?Explain about native modifier?Explain about volatile modifier?What is mean by synchronisation?Why would you use a synchronized block verses synchronized method?What is interface?Can you write an interface without any methods?What do you call the interface without any members?How can you force your programmer to implement only the features of your class?Can we declare a class as abstract and final?Can we override abstract methods?Can we implement one interface from another?Why the method of interfaces are public and abstract by default?Can we write a class with in an interface?What is the difference between an interface and an abstract class?Can we create an object to interface?When we go for abstract and interface in java?Why we use interfaces?What is the difference between a class and an abstract class?What is the difference between an interface and an abstract class?What is class loader and explain types of class loaders?Explain about system class loader?Explain Annotations in java?Explain about memory management in java?Is String a class or data type?String s = “ pooji ” ;    String s1 = new String(“ pooji”);   System.out.println(s=s1);System.out.println(s.equals(s1)); What is the output? What is object reference?What is the difference between == and equals() while comparing String? Which one is reliable?What is string constant pool?Why overrides equals() and hashcode()?What is difference between String and StringBuffer classes?What is main different between StringBuffer and StringBuilder classes?What is an Error?Write an exception hierarchy?What is an Exception?What is the difference between error and an Exception?What is mean by Exception handling?What are the types of Exceptions?What is throwable?What is the super class for all Exceptions?What is the difference between throws and throw?Is it possible to re-throw exceptions?What is the purpose of finally block?What is the purpose of finalization?Explain final, finally, finalization?If i write system.exit(0); at the end of the try block, will the finally block will execute?If i write return at the end of try block, will the finally block will execute?How to create user defined exceptions?How to override methods in exception handling?Can a top level class be private or protected?What is the default value of an object reference declared as an instance     variable Is it necessary that each try block must be fallowed by  a catch block?What is fail fast exception?How can you call the garbage collector?What is the scope of default access specifier?What is the difference between return and system.exit(0)?What is difference between System.exit(0) and system.exit(1);Write collection hierarchy?What are limitations of object Arrays?What are differences between arrays and collections?What is Collection API ?What is Collection framework?What  is difference between Collections and Collection?Explain about Collection interface?Explain about List interface?Explain about Set interface?Explain about SortedSet interface?Explain about NavigableSet ?Explain about Queue interface?Explain about Map interface?Explain about SortedMap ?Explain about NavigableMap?Explain about ArrayList class?What is RandomAccess Interface?Explain about LinkedList class?Explain about Vector class?What is difference between ArrayList and Vector?How we can get synchronized version of ArrayList?What is difference between size and capacity of a Collection Object?What is difference between ArrayList and Linked List?What are legacy classes and interfaces present  in Collections framework?What is difference Enumeration and Iterator?What are limitations of Enumeration?What is difference between enum and Enumeration?What is difference between Iterator and ListIterator?What is relation between ListIterator and Iterator?Explain about HashSet class?If we are trying to insert duplicate values in Set what will happen?What is LinkedHashSet?Differences  between HashSet and LinkedHashSet?Explain about TreeSet?What are differences between List and Set interfaces?What is Comparable interface?What is Comparator interface?What are differences between Comparable and Comparator?What is difference between HashSet and TreeSet?What is Entry interfaceExplain about HashMap?Explain about LinkedHashMap?Differences between HashMap and LinkedHashMap ?Differences between HashMap and Hashtable?What is IdentityHashMap?What is TreeMap?What is Hashtable?Why ArrayList is faster than Vector?  What is introspection in java?What is a reflection? How can you achive in java?What is resource bundle?Which thread always runs in a java program by default?Why threads are called light_weight?How can you stop a thread in java?Which method is executed by the thread by default?What is the difference between synchronized block and synchronized keyword?What is thread deadlock?What is difference between the sleep() and wait() methods?What is default priority of a thread?What is a daemon thread?What is thread life cycle?What is the difference between extends thread and implements runnable? Which one is advantageous?How to create a thread?What is serialization?What is externalization?How to prevent serialization?What is wrapper class?What is difference between int and Integer?Objects are passed by value or passed by reference?Primitive data types are passed by value or passed by reference?What is difference between shallow copy and deep copy?