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Core java - Interview Questions and Answers for 'Oracle' - 11 question(s) found - Order By Newest

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q1. What is a final method ?Core Java
Anonymous
Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.

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  Q2. What is a String Pool ?Core Java
Anonymous
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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  Q3. Difference between Vector and ArrayList ?Core Java
Anonymous
Ans. Vectors are synchronized whereas Array lists are not.

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 Q4. Can we access instance variables within static methods ?Core Java
Anonymous
Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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   Like      Discuss      Correct / Improve     java   oops   static   static methods   java keywords     Oracle


Very frequently asked in phone and walk in interviews.
  Q5. What are Marker Interfaces ? Name few Java marker interfaces ?Core Java
Anonymous
Ans. These are the interfaces which have no declared methods.Serializable and cloneable are marker interfaces.

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Very frequently asked. Usually asked with questions related to String.
  Q6. What is an Immutable Object ?Core Java
Anonymous
Ans. Object that can't be changed after instantiation.

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 Q7. Is it necessary that each try block to be followed by catch block ? Core Java
Anonymous
Ans. It should be followed by either catch or finally block.

  Sample Code for Retry in case of exception

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Frequently asked in CTS ( Based on 2 feedback )
  Q8. What is the difference between comparable and comparator in java.util pkg?Core Java
Admin
info@buggybread.com
Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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 Q9. How finally used under Exception Handling?Core Java
Admin
info@buggybread.com
Ans. The finally keyword is used to create a block of code that follows a try block. A finally block of code always executes, whether or not an exception has occurred.

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   Like      Discuss      Correct / Improve     java   exceptions   exception handling   try   finally   basic interview question     Oracle Engineering Group

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 Q10. What was the driving force to introduce default methods in Interfaces wef from Java 8 ?Core Java2016-07-14 14:36:49

Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs.

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 Q11. Can we override wait() or notify() ?Core Java2017-09-13 14:17:15

Ans. No, because these are final.

public final void wait() throws InterruptedException

public final void notify()

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   Like      Discuss      Correct / Improve     wait  notify     Oracle




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