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| Interview Questions and Answers - Order By Rating | ||||
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| Ans. DAO is Data Access Object which is used within Persistence Layer to make Database Transaction. For example , the class holding the Database connection and CRUD methods. | ||||
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| Ans. DTO is Data Transfer Object i.e Pojo which is supposed to move between different layers of software architecture for transferring information. Example could be the object passed from client in case of web service call or the object passed to Persister for Database Persistence. | ||||
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| Discuss Correct / Improve DTO Data Transfer Object basic frequent | ||||
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| Ans. CRUD stands for "Create, read, update and delete" are the basic functions of persistence. | ||||
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Discuss Correct / Improve CRUD Persistence Database Database Operations  Asked in 3 Companies Basic frequent | ||||
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| Ans. No, Its an Operator. | ||||
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| Discuss Correct / Improve new keyword operator | ||||
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| Ans. Fail Safe systems are tolerant systems that continue processing even if they sense any problem. the objective here is to continue with the processing even if there are some problems instead of completely shutting it down. Example could be to catch an exception and still letting it complete with partial results. | ||||
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| Discuss Correct / Improve fail safe systems system design exception handling Asked in 3 Companies | ||||
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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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| Discuss Correct / Improve fail-fast Iterators Iterators Asked in 5 Companies intermediate | ||||
 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. Car Engine is an example of encapsulation and abstraction. You ignite the car using an interface called starter and least bothered about how the tire actually moves (This is abstraction). The engine encapsulates the complete process to itself only and doesn't allow you to start the other components like the radiator etc ( this is excapsulation ) | ||||
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| Discuss Correct / Improve encapsulation object oriented programming (oops) oops concepts abstraction oops oops features java features Asked in 13 Companies | ||||
| This question can be asked in different variants like performace improvement of an application, improving performance for DB communication etc. | ||||
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| Ans. This depends on entirely upon the code type. For example 1.If its just logic, we can try it to short circuit or put the if / switch case with maximum probability in the beginning. 2. Can use faster data structures, for eg - random retrieval instead of sequence / iterator 3. Working with primitive types or even bytes instead of Objects, even though it may result in marginal improvement. 4. If its service call, then service call with bulk load can help 5. If DB Operation, then with use of Indices , Views or using ORM , cache etc. | ||||
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| Discuss Correct / Improve performance improvement code optimization Asked in 1 Companies | ||||
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| Ans. Declaration is intimation to the compiler about the nature of Data a reference is going to hold. For example - List myList; Instantiation is reservation of memory. For example myList = new ArrayList(); Initialization or construction is setting the default values for member elements. For example myList = new ArrayList(mySet); ** Example 2nd is both for instantiation as well as initialization. The only difference is that 2nd will initialized the member elements to their default values whereas 3rd will initialized it with the elements from set. | ||||
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| Discuss Correct / Improve declaration instantiation initialization construction declaration vs instantiation instantiation vs initialization declaration vs initialization Asked in 1 Companies basic frequent | ||||
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| Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification. | ||||
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| Discuss Correct / Improve cookie javascript web application session management browser j2ee Asked in 16 Companies basic frequent | ||||
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| Ans. Simple Inner Class, Local Inner Class, Anonymous Inner Class, Static Nested Inner Class. | ||||
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| Discuss Correct / Improve java inner classes classes Asked in 6 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. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly. | ||||
 Sample Code for treemap Sample Code for hashmap | ||||
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| Discuss Correct / Improve java collections map treemap hashmap treemap vs hashmap Asked in 31 Companies basic frequent | ||||
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| Very Frequently asked across all type of companies and across all levels. | ||||
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| Ans. Private - Not accessible outside object scope. Public - Accessible from anywhere. Default - Accessible from anywhere within same package. Protected - Accessible from object and the sub class objects. | ||||
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| Discuss Correct / Improve java oop access specifier public private default protected public vs private vs default vs protected Asked in 12 Companies basic frequent | ||||
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| Ans. Multiple servlets serving the request in chain. | ||||
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| Discuss Correct / Improve java web application servlets Asked in 1 Companies rare | ||||
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| Ans. boolean - java.lang.Boolean byte - java.lang.Byte char - java.lang.Character double - java.lang.Double float - java.lang.Float int - java.lang.Integer long - java.lang.Long short - java.lang.Short void - java.lang.Void | ||||
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| Discuss Correct / Improve java java5 data types wrapper classes adapter design pattern rare | ||||
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| Ans. Generics , Enums , Autoboxing , Annotations and Static Import. | ||||
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| Discuss Correct / Improve java java5 generics enum autoboxing annotations static import rare | ||||
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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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| Discuss Correct / Improve java constructor object creation intermediate rare | ||||
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| Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler. | ||||
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| Discuss Correct / Improve static static method java oop variables Asked in 1 Companies basic frequent | ||||
| Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems | ||||
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| Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory. x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object. Sample code: String x = new String("str"); String y = new String("str"); System.out.println(x == y); // prints false System.out.println(x.equals(y)); // prints true | ||||
| Sample Code for equals | ||||
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| Discuss Correct / Improve java string comparison string object class == equals object equality operator == vs equals equals vs == Asked in 294 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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| Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. | ||||
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| 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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| Discuss Correct / Improve java oops final final method Asked in 30 Companies basic frequent | ||||
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| Frequently asked. | ||||
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| Ans. Iterator is an interface that provides methods to iterate over any Collection. | ||||
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| Discuss Correct / Improve java collections iterator Asked in 11 Companies basic frequent | ||||
| Very frequently asked across all types of companies. | ||||
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| Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values. | ||||
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| Discuss Correct / Improve java collections hashmap map hashtable hashmap vs hashtable Asked in 14 Companies basic frequent | ||||
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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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| Discuss Correct / Improve java oops static static method overriding intermediate | ||||
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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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| 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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| Discuss Correct / Improve serialization java oops static static variables Asked in 1 Companies intermediate rare | ||||
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| Ans. They both represent the long primitive type. They are exactly the same. | ||||
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| Discuss Correct / Improve java data types long.Class long.TYPE advanced expert 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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| Discuss Correct / Improve java this object reference constructor chaining intermediate rare | ||||
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Which of the following file is called deployment descriptor ?
