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| Ans. 1)The overriding methods can throw any runtime Exception , here in the case of runtime exception overriding method (subclass method) should not worry about exception being thrown by superclass method. 2)If superclass method does not throw any exception then while overriding, the subclass method can not throw any new checked exception but it can throw any runtime exception 3) Different exceptions in java follow some hierarchy tree(inheritance). In this case , if superclass method throws any checked exception , then while overriding the method in subclass we can not throw any new checked exception or any checked exception which are higher in hierarchy than the exception thrown in superclass method | ||||
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| Ans. Combine the data of our application and its manipulation at one place. Encapsulation Allow the state of an object to be accessed and modified through behaviors. Reduce the coupling of modules and increase the cohesion inside them. | ||||
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Discuss Correct / Improve java oops oops concepts encapsulation object oriented programming (oops) oops concepts basic interview question  Asked in 2 Companies  basic  frequent | ||||
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| Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects. In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects. From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects. | ||||
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| Ans. No. Enums are final by design. | ||||
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| Discuss Correct / Improve java enums inheritance object oriented programming (oops) oops concepts yes-no Asked in 1 Companies intermediate | ||||
| Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews. | ||||
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| Ans. Composition - has-a relationship between objects. Inheritance - is-a relationship between classes. Composition - Composing object holds a reference to composed objects and hence relationship is loosely bound. Inheritance - Derived object carries the base class definition in itself and hence its tightly bound. Composition - Used in Dependency Injection Inheritance - Used in Runtime Polymorphism Composition - Single class objects can be composed within multiple classes. Inheritance - Single class can only inherit 1 Class. Composition - Its the relationship between objects. Inheritance - Its the relationship between classes. | ||||
 Sample Code for inheritance Sample Code for composition | ||||
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| Ans. Derived object carries the body of its class as well as the body of the parent class. Its body ( member elements ) is initialized using its own class constructor whereas the body ( member elements ) carried from the parent class are initialized using super class constructor. So In order to initialize the elements of the parent class before its own elements are even initialized, super is called. | ||||
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| Ans. Abstraction is provided in Java by following ways - Coding to the ( Interfaces / Abstract Classes ) or contracts By Encapsulating details within classes and exposing the minimal Door ( few public methods ) | ||||
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| Ans. No. This will result in compilation error as Polymorphism cannot be performed on Object types. | ||||
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| Ans. Stateless objects are the objects without instance fields (instance variables). The class may have compile time constants i.e static final fields.Immutable objects are the objects which have state but the state cannot be changed after initialization. Both are Thread safe. | ||||
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| Ans. They can be shared across multiple threads as they are thread safe. | ||||
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| Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals. | ||||
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| Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class. | ||||
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| Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding. | ||||
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| Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance. With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance. | ||||
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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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Which of the following Java feature promotes access protection or Hiding ?
