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| Interview Questions and Answers for 'Persistent System' - 11 question(s) found - Order By Rating | ||||
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| Ans. There are four main OOP concepts in Java. These are: Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times. Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide. Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel. Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below. | ||||
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 Discuss Correct / Improve  oops oops concepts  Asked in 16 Companies  basic  frequent | ||||
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| Ans. Games are very good examples of threading.You can use multiple objects in games like cars, motor bikes, animals, people etc. All these objects are nothing but just threads that run your game application. | ||||
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| Discuss Correct / Improve threads multithreading Asked in 1 Companies | ||||
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| Ans. Following Classes in Java SE creates immutable objects String class Wrapper Classes like Integer, Float etc. StackTraceElement Most Enum classes File Class Locale Class | ||||
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| Discuss Correct / Improve immutable immutability objects immutable immutability Asked in 1 Companies Basic frequent | ||||
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| Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance | ||||
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| Discuss Correct / Improve core oops concepts Asked in 65 Companies basic frequent | ||||
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| Ans. Shutdown hook is a thread that is invoked implicitly by JVM just before the shut down. It is used to clean up unused resources. | ||||
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 Basic and Very Frequently asked. | ||||
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| Ans. Polymorphism means the condition of occurring in several different forms. Polymorphism in Java is achieved in two manners 1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas 2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding. | ||||
 Sample Code for overloading Sample Code for overriding | ||||
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| Discuss Correct / Improve polymorphism object oriented programming (oops) oops concepts oops concepts Asked in 108 Companies Basic frequent | ||||
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| 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 to fresh graduates. | ||||
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| Ans. Process is a program in execution whereas thread is a separate path of execution in a program. | ||||
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| Discuss Correct / Improve java threads multi threading operating system process vs thread Asked in 24 Companies basic frequent | ||||
| Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com | ||||
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| Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy. | ||||
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| Discuss Correct / Improve hibernate Asked in 16 Companies basic frequent | ||||
| Frequently asked question in companies using Hibernate. | ||||
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| Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded. | ||||
| Sample Code for Lazy Initialization | ||||
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| Discuss Correct / Improve hibernate lazy loading hibernate lazy initialization hibernate architecture Asked in 77 Companies Basic frequent | ||||
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| Frequently asked at Manhattan Associates ( Based on 2 feedback ) | ||||
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| Ans. Its an anonymous method without any declaration. Lambda Expression are useful to write shorthand Code and hence saves the effort of writing lengthy Code. It promotes Developer productivity, Better Readable and Reliable code. | ||||
| Sample Code for lambda | ||||
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| Discuss Correct / Improve java java8 lambda expression architecture Asked in 58 Companies expert frequent | ||||
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Static Polymorphic in Java is achieved through .. 
