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| Ans. AMI is an Amazon Machine Image. It contains the configuration to enable to boot up an EC2 instance with said configuration whereas Cloud formation is a templating language that allows to describe how to build a VPC and also allows you to create AWS services AMI is templating specific to instances whereas the scope of CloudFormation templating is much bigger. CloudFormation could use AMI for launching instances along with other services. | ||||
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 Discuss Correct / Improve  aws cloud formation aws ami amazon ami aws ami amazon ami vs aws cloud formation | ||||
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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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Discuss Correct / Improve session session management java cookies authentication web application ebay  intermediate | ||||
 Frequently asked to fresh graduates. | ||||
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| Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities. Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn. Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish. Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method. Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes. Blocked on synchronization - Will move to Runnable when a lock is acquired. Dead - The thread is finished working. | ||||
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Discuss Correct / Improve java threads multi threading scheduling thread states basic interview question  Asked in 1 Companies basic  frequent | ||||
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| Ans. A Stream is an abstraction that either produces or consumes information. There are two types of Streams : Byte Streams: Provide a convenient means for handling input and output of bytes. Character Streams: Provide a convenient means for handling input & output of characters. Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream. Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer. | ||||
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| Discuss Correct / Improve java file io streams byte stream character stream file handling Asked in 3 Companies | ||||
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| Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap. | ||||
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| Discuss Correct / Improve java collections hashmap map concurrenthashmap concurrenthashmap concurrency general electric ge Asked in 32 Companies rare | ||||
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| Ans. HBM Files ( Mapping ) DB Connection ( DB Connection String , User Name , Password , Pool Size ) SQL Dialect ( SQL variant to be generated ) Show SQL ( Show / No show SQL on Console ) Auto Commit ( True / False ) | ||||
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| Discuss Correct / Improve hibernate configuration barclays Asked in 11 Companies | ||||
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| Ans. Predicate represents an anonymous function that accepts one argument and produces a result. Supplier represents an anonymous function that accepts no argument and produces a result. Consumer represents an anonymous function that accepts an argument and produces no result. | ||||
 Sample Code for Predicate Sample Code for Supplier Sample Code for Consumer | ||||
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| Discuss Correct / Improve java java8 predicate consumer supplier lambda expression predicate vs consumer vs supplier expert | ||||
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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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| Discuss Correct / Improve java db database hibernate orm at&t overstock.com performance improvement architecture technical lead architect intermediate | ||||
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| Ans. List | ||||
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| Discuss Correct / Improve collections java sorting | ||||
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| Ans. Encapsulation | ||||
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| Discuss Correct / Improve java java concepts java features oops concepts oops features access protection information hiding | ||||
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| Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods. | ||||
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| Discuss Correct / Improve parameter argument method function parameter vs argument basic | ||||
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| Ans. There are 2 reasons for it. 1. Usage of Primitive types - Though Java provides classes for the primitive data types but as the usage of primitives is permissible, its considered unpure OOP's language. 2. Usage of Static members - Static members belong to the class and not objects and hence not considered fit for pure OOP's programming. | ||||
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| Discuss Correct / Improve oops object oriented programming object oriented language primitive data types Asked in 2 Companies | ||||
| Frequently asked. Among first few questions in the J2EE segment of interview. | ||||
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| Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following * Servlet entries and url mapping * Plugins * Some info regarding authentication / filters * Landing Page * Event Handlers | ||||
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| Discuss Correct / Improve web.xml servlets deployment descriptor Asked in 15 Companies basic frequent | ||||
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| Ans. HashTable has been deprecated. As an alternative, ConcurrentHashMap has been provided. It uses multiple buckets to store data and hence much better performance than HashTable. Moreover, there is already a raw type HashMap. The only difference between the HashTable and HashMap is that Hashtable is synchronized whereas HashMap is not. Most of the synchronized collections have been deprecated and their raw alternative have been presented as preferred.Synchronization has a cost. Using synchronized collection in places where there is no need of it leads to useless utilization of resources. As these collections are rarely used in a static context or shared among threads, Java might have thought it better to just provide the raw collection and let developers implement synchronization if he feels the need to do so. HashMap is now presented as the default and the preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable. Because of this, Java thought it right to deprecate the use of HashTable.' Synchronization has a cost. Using synchronized collection at a place where there is hardly any need of it would means useless utilization of resources. As these collections are rarely used in static context or shared among threads, Java might have thought it better to just provide the raw collection and let developer implement synchronization if he feels the need to do so. As HashMap has been presented as default and preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable, Java thought it right to deprecate the use of HashTable. | ||||
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| Discuss Correct / Improve hashtable synchronized collections Why synchronized collections have been deprecated Why HashTable has been deprecated HashTable vs HashMap expert | ||||
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| Ans. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type ) 2. TreeSet doesnt allow null elements whereas HashMap does. 3. As TreeSet orders elements and is hence insertion is comparatively slower. 4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time. 5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally. | ||||
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| Discuss Correct / Improve collections hashset treeset set hashet vs treeset Asked in 4 Companies Basic frequent | ||||
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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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| Discuss Correct / Improve serialization Asked in 1 Companies intermediate frequent | ||||
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| Ans. First expects the argument as a string array whereas second expects variable number of string arguments or a string array. So we can call both by providing string array as an argument but second can be called with 0 to n string arguments which cannot be done for first. for example - We can call second method with any of following method(); method("Hello"); method("Hello","World"); method(new String[4]); | ||||
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| Discuss Correct / Improve var args methods method declarations functions | ||||
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| Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5. So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5. | ||||
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| Discuss Correct / Improve arrays array initialization | ||||
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| Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other. Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption. | ||||
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| Discuss Correct / Improve aws region aws availability zone aws edge location region vs availabillity zone | ||||
| Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs ) | ||||
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| Ans. List - Members are stored in sequence in memory and can be accessed through index. Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates. Map - Contains Key , Value pairs. | ||||
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| Discuss Correct / Improve java collections list set map list vs set vs map Asked in 8 Companies basic frequent | ||||
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| Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance. | ||||
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| Discuss Correct / Improve java oop oop concepts inheritence multiple inheritence basic interview question Asked in 10 Companies basic frequent | ||||
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| Frequently asked at HCL Technologies ( Based on 3 feedback ) | ||||
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| Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked. | ||||
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| Discuss Correct / Improve java exceptions checked exceptions unchecked exceptions exception handling checked vs unchecked exceptions Asked in 39 Companies basic frequent | ||||
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| Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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| Ans. Final variable is a variable constant that cannot be changed after initialization. | ||||
| Sample Code for final variable | ||||
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| Discuss Correct / Improve oops java final final variable basic interview question Asked in 12 Companies basic frequent | ||||
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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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| Discuss Correct / Improve serialization java oops static static variables Asked in 1 Companies intermediate rare | ||||
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| Ans. Yes , for HashMap. HashMap implements Map interface. HashMap allows one null key and any number of null values. | ||||
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| Discuss Correct / Improve java collections hashmap map hashtable yes-no Asked in 1 Companies | ||||
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| Ans. One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializable Exception. | ||||
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| Discuss Correct / Improve serialization java oops object expert | ||||
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| Ans. Vectors are synchronized whereas Array lists are not. | ||||
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| Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent | ||||
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| Ans. It in Java is used to indicate that a field should not be serialized. | ||||
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| Discuss Correct / Improve java oops serialization transient java keywords Asked in 39 Companies intermediate frequent | ||||
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| Very Frequently asked. Usually asked along with String Class related questions. | ||||
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| Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created. | ||||
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| Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent | ||||
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| Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation. Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation. Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types. | ||||
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| Discuss Correct / Improve java oops constructor object instantiation | ||||
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What is the initial state of a thread when it is created and started ?
