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Interview Questions and Answers - Order By Newest | ||||
Frequently asked to fresh graduates. | ||||
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Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions. Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback. Consistency means that any transaction should lead database from one stabe state to another. Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially. Durability means that when a transaction is committed it forms the permanent state of database. | ||||
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Like Discuss Correct / Improve  database  acid Asked in 7 Companies Intermediate | ||||
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Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused. 2. As there is no object in Static class, it cannot participate in runtime Polymorphism. 3. As Static class doesnt allow creating objects and hence it cannot be serialized. 4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need. 5. Its not recommended to use pure static class as it fails to use many OOPs concepts. | ||||
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Like Discuss Correct / Improve  Static Class  Singleton  Static Class vs Singleton Asked in 3 Companies Intermediate   frequent | ||||
Very frequently asked in companies using SOA. | ||||
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Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines - 1. http for client server communication, 2. XML / JSON as formatiing language , 3. Simple URI as address for the services and, 4. stateless communication. | ||||
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Like Discuss Correct / Improve  java   web services   rest   java   j2ee  architecture Asked in 14 Companies intermediate   frequent | ||||
Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc ) | ||||
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Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility. | ||||
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Like Discuss Correct / Improve  design patterns   ioc ( Inversion of Control )  dependency injection Asked in 83 Companies intermediate   frequent | ||||
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Ans. New operator in Java creates objects. Constructor is the later step in object creation. Constructor's job is to initialize the members after the object has reserved memory for itself. | ||||
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Like Discuss Correct / Improve  java   constructor   object creation intermediate   rare | ||||
Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM. | ||||
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Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached. | ||||
Sample Code for volatile | ||||
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Like Discuss Correct / Improve  java   oops   synchronization   volatile   java keywords Asked in 42 Companies intermediate   frequent | ||||
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Ans. Modularity - First sign of good code is whether it has been segregated into methods and classes appropriately. I dont mind it in excess because I believe that is forward looking strategy as applications tends to expand and eventually become hard to read. Self Explanatory - Variables and methods should be named in a way that the code should be self explanatory even without comments. Use of Constant variables to explain use of literal. Proper Code Reuse - If there is anything being reused , it should be moved to parent classes / methods. Proper composition calls - Composed hierarchy should not be access in just single line. One or two levels is ok but having multiple levels make it hard to read and debug. | ||||
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Like Discuss Correct / Improve  code review  clean code Asked in 1 Companies intermediate   frequent | ||||
Frequently asked to fresh graduates and less experienced developers. | ||||
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Ans. 1. Multithreading provides better interaction with the user by distribution of task 2. Threads in Java appear to run concurrently, so it provides simulation for simultaneous activities.The processor runs each thread for a short time and switches among the threads to simulate sim-ultaneous execution (context-switching) and it make appears that each thread has its own processor.By using this feature, users can make it appear as if multiple tasks are occurring simultaneously when, in fact, each is running for only a brief time before the context is switched to the next thread. 3. We can do other things while waiting for slow I/O operations.In the java.iopackage, the class InputStreamhas a method, read(), that blocks until a byte is read from the stream or until an IOExceptionis thrown. The thread that executes this method cannot do anything elsewhile awaiting the arrival of another byte on the stream. | ||||
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Like Discuss Correct / Improve  java   threads   multi threading  concurrency   multithreading Asked in 5 Companies intermediate   frequent | ||||
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Ans. Cookie and Session are used to store the user information. Cookie stores user information on client side and Session does it on server side. Primarily, Cookies and Session are used for authentication, user preferences, and carrying information across multiple requests. Session is meant for the same purpose as the cookie does. Session does it on server side and Cookie does it on client side. One more thing that quite differentiates between Cookie and Session. Cookie is used only for storing the textual information. Session can be used to store both textual information and objects. | ||||
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Like Discuss Correct / Improve  session   session management   java   cookies   authentication   web application   ebay intermediate | ||||
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Ans. We can make a class immutable by 1. Making all methods and variables as private. 2. Setting variables within constructor. Public Class ImmutableClass{ private int member; ImmutableClass(int var){ member=var; } } and then we can initialize the object of the class as ImmutableClass immutableObject = new ImmutableClass(5); Now all members being private , you cant change the state of the object. | ||||
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Like Discuss Correct / Improve  java   oops   immutable  immutability   immutable  immutability class   technical lead Asked in 5 Companies intermediate   frequent | ||||
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Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements ) 2. Restructuring Indexes. 3. DB Caching Tuning ( if using ORM ) 4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM ) | ||||
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Like Discuss Correct / Improve  java   db   database   hibernate   orm   at&t   overstock.com   performance improvement   architecture   technical lead   architect intermediate | ||||
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Ans. 1. Objects are serialized and not classes and hence Static variables are ignored. 2. Transient is an explicit declaration to ignore the variable during serialization and hence transient instance variables are ignored too. 3. Base class instance variables if the base class hasn't been declared serializable. | ||||
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Like Discuss Correct / Improve  serialization Asked in 1 Companies intermediate   frequent | ||||
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Ans. They are loaded at runtime when the respective Class is loaded. | ||||
Sample Code for static variable | ||||
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Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object. | ||||
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Like Discuss Correct / Improve  serialization   java   oops   static   static variables Asked in 1 Companies intermediate   rare | ||||
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Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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Like Discuss Correct / Improve  java   oops   serialization   transient   java keywords Asked in 39 Companies intermediate   frequent | ||||
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Very frequently asked in phone and walk in interviews. | ||||
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote | ||||
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Like Discuss Correct / Improve  java   oops   interfaces   marker interface   serializable   clonable Asked in 21 Companies intermediate   frequent | ||||
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Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance. | ||||
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Like Discuss Correct / Improve  java   oops   class casting   classcastexception   exception   error Asked in 4 Companies intermediate   frequent | ||||
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Ans. Iterators in java are used to iterate over the Collection objects. Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element. Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection. | ||||
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Like Discuss Correct / Improve  ail fast   fail saf Asked in 9 Companies intermediate | ||||
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Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections. | ||||
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Like Discuss Correct / Improve  java   collections   treemap   treeset   comparator Asked in 2 Companies Intermediate | ||||
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Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly. | ||||
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Like Discuss Correct / Improve  java   main method   overloading   yes-no Asked in 6 Companies intermediate   frequent | ||||
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Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it. | ||||
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Like Discuss Correct / Improve  java   collections   concurrentmodificationexception   exception  concurrency Asked in 14 Companies intermediate | ||||
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Ans. JSON.stringify() turns an object into a JSON text and stores that JSON text in a string. So If we stringfy above notation , it will become {"name":"xyz","gender":"male";"age":30} | ||||
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Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class. | ||||
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Like Discuss Correct / Improve  java   import   jvm   advanced Asked in 1 Companies intermediate   rare | ||||
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Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior. A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable. | ||||
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Ans. Class , Heap , Stack , Register , Native Method Stack. | ||||
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Ans. No Abstract methods can only be declared protected or public. | ||||
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Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. | ||||
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Like Discuss Correct / Improve  java   serialization   externalizable interface Asked in 2 Companies intermediate   rare | ||||
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Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class. | ||||
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Like Discuss Correct / Improve  java   oops   object instantiation   object creation   class.forname   newinstance   new operator   difference between   advanced intermediate | ||||
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Ans. 1. Collection should have an index for random access. 2. Collection should have ordered elements. | ||||
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Like Discuss Correct / Improve  java   collections   search algorithm   search   binary search   at&t intermediate | ||||
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Ans. true, due to String Pool, both will point to a same String object. | ||||
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