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Interview Questions and Answers - Order By Rating | ||||
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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. finally will execute in all graceful situations - graceful executions as well as graceful exceptions. The only situation when finally block won't execute is when the app is abruptly stopped, killed or unplugged. | ||||
Sample Code for finally | ||||
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Like Discuss Correct / Improve  finally Intermediate | ||||
Frequently asked in high end product companies. | ||||
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Ans. https://www.geeksforgeeks.org/lru-cache-implementation/ | ||||
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Like Discuss Correct / Improve  cache  LRU cache  coding  code Asked in 10 Companies intermediate | ||||
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Ans. If the process / app is abruptly killed or terminated. | ||||
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Like Discuss Correct / Improve  exception handling  finally Asked in 2 Companies intermediate | ||||
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Ans. https://en.wikipedia.org/wiki/Database_normalization | ||||
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Like Discuss Correct / Improve  normalization  database Asked in 35 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 in Alibaba (Based on 2 feedback) | ||||
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Ans. In Java JVM memory settings is done by use the arguments -Xms -Xmx. Use M or G after the numbers for indicating Megs and Gigs of bytes respectively. -Xms indicates the minimum and -Xmx the maximum. | ||||
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Like Discuss Correct / Improve  jvm  memory management  jvm best memory setting Asked in 1 Companies intermediate | ||||
Very Frequently asked to Senior Software Engineers or Developers. | ||||
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Ans. [Open Ended Answer] | ||||
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Like Discuss Correct / Improve  design patterns Asked in 17 Companies intermediate   frequent | ||||
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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 | ||||
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Ans. Please not that all such questions can be easily answered through recursion. Simple recursive implementation could be traverse(root); void traverse(Element element){ if(element.hasNext()){ traverse(element.next()); } else { System.out.println(element); } } but this algo / code lead to endless loop if there is a loop in graph traversal. So you can keep a collection to keep track of which elements have laready been traversed static List<Elements> listOfAlreadyTraversedElements = new ArrayList<Elements>(); main(){ traverse(root); } void traverse(Element element){ if(element.hasNext()){ traverse(element.next()); } else { listOfAlreadyTraversedElements.add(element); System.out.println(element); } } | ||||
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Like Discuss Correct / Improve  graph traversal algorithm  graph traversal algorithm using recursion Asked in 1 Companies intermediate | ||||
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Ans. There is a Java system property "sun.arch.data.model" that can tell if JVM is 32 bit of 64 bit System.getProperty("sun.arch.data.model") can be used to get that property. | ||||
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Like Discuss Correct / Improve  jvm intermediate   rare | ||||
Usually asked with Questions related to Generics. | ||||
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Ans. Type erasure applies to the use of generics. When generics are used, they're pre compiled into compile time checks and execution-time casts. | ||||
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Like Discuss Correct / Improve  type erasures  generics Asked in 2 Companies intermediate   rare | ||||
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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Frequently asked Design Pattern interview question. | ||||
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Ans. The prototype pattern is a creational design pattern. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. Prototype is used when we need duplicate copies of objects. | ||||
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Like Discuss Correct / Improve  design pattern  prototype design pattern  cloning Asked in 11 Companies intermediate | ||||
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Ans. We can use external table feature of Oracle. | ||||
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Like Discuss Correct / Improve   Asked in 1 Companies Intermediate | ||||
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Ans. Yes, with finally. Yes, finally block will be executed even if there is no exception in try block. If finally throws an exception, the exception gets thrown to the calling module. | ||||
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Like Discuss Correct / Improve  exception handling Asked in 1 Companies intermediate | ||||
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Ans. It depends on whether the request object is persisted as it is or its first dismantled, modified or refactored and then inserted into DB. In first case, it should be a PUT request whereas in second case it should be a POST Request. | ||||
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Like Discuss Correct / Improve  Put vs Post   Rest Asked in 2 Companies intermediate   frequent | ||||
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Ans. Fail-fast iterators detect illegal concurrent modification during iteration and fail quickly and cleanly rather than risking arbitrary, non deterministic behavior at an undetermined time in future. Example could be of an Iterator failing if it smells ConcurrentModificationException. | ||||
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Like Discuss Correct / Improve  fail-fast Iterators  Iterators Asked in 5 Companies intermediate | ||||
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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 | ||||
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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. | ||||
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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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Like Discuss Correct / Improve  java   oops   static   static variable   memory intermediate | ||||
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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. "this" keyword is a reference to the current object and can be used for following - 1. Passing itself to another method. 2. Referring to the instance variable when local variable has the same name. 3. Calling another constructor in constructor chaining. | ||||
Sample Code for this keyword | ||||
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Like Discuss Correct / Improve  java   this   object reference   constructor chaining intermediate   rare | ||||
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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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Frequently asked in all types of companies especially Indian Services companies. Frequently asked in CTS (Based on 2 feedback) | ||||
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Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not. | ||||
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Like Discuss Correct / Improve  java   collections   hashcode   advanced  hashtable Asked in 33 Companies intermediate   frequent | ||||
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Ans. Transient variables are variable that cannot be serialized. | ||||
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Like Discuss Correct / Improve  java   serialization   transient Asked in 15 Companies intermediate   rare | ||||
Frequently asked in Infosys India | ||||
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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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Like Discuss Correct / Improve  java   oops   string   string class   string pool   heap memory Asked in 31 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 | ||||
Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback) | ||||
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Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected. | ||||
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Like Discuss Correct / Improve  java   garbage collection   java memory management   advanced Asked in 21 Companies intermediate   frequent | ||||
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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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Like Discuss Correct / Improve  json   JSON.stringify intermediate   rare | ||||