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Object Oriented Programming is concept of handling object in different ways ,
There are four pillars of OOPS concept:
Inheritance is mechanism to acquire property and behaviour of parent object to its child .
“extends” keyword is used for implementation of inheritance.
Inheritance represents the IS-A relationship which is also known as a parent-child relationship.
To avoid method ambiguity java does not support multiple inheritance. Since, Every child class extend parent property when JVM call parent property ,but it will confused which parent property will be acquired .
“Poly” means many and “Morphs” means forms .
When a Object achieve multiple property or forms according to its requirement , it is known as Polymorphism
ex: Myself on home behaves as part of family where as Myself in office as senior software engineer behaves as part of Organisation
| Compiletime Polymorphism | Runtime Polymorphism |
|---|---|
| when object is binded at compile time with functionality ,it is known as Compiletime Polymorphism | whenever object is binded at runtime with functionality , it is known as Runtime Polymorphism |
| it is also known as Early binding or Static binding | it is also known as late binding or dynamic binding |
| it can be achieved through Method Overloading | it can be achieved through Method Overriding |
| it does not require inheritance | it require inheritance |
| Method Overloading | Method Overriding |
|---|---|
| in method Overloading method name must be same and signature or Parameter must be different either no of parameter or name of parameter | Method Overriding method name, parameter and return type must be same only implementation will be changed |
| Inheritance is not required | Inheritance is required |
| return type may be same or different | return type must be same |
| perform at compiletime only | perform at runtime only |
The main method can be overloaded but cannot be overridden in Java.
when we overload main method , JVM still run original method ,it will never call our overloaded main method.
overriding is not happening in the case of main method as it is static method which is independent of object creation and overriding is binding of object only
No, we can not override any static method as it belong to class level initialization rather then object level.
Hiding the implementation showing only the functionality to the user is known as Abstraction.
Abstraction solve problem at design level.
ex: Television
it can be achieved by interface and abstract class.
| Abstract class | Interface |
|---|---|
| Abstract class can have both abstract and non-abstract method | Interface can have only abstract method |
| Non static and Non final variable are also allowed | Only Static and Final variable are allowed |
| does not support multiple inheritance | support multiple inheritance |
| Abstract class can be extended | interface can be implemented |
| Data member are private and protected | Data member are public only |
Encapsulation is wrapping data and code together in a single unit .it is used for data hiding purposes . it can be achieved through getter an setter method Java Bean Class is best example of it. it solve the problem on implementation level.
Association is connection between two classes that are set up through their objects .
There are different types of association
| Aggregation | Composition |
|---|---|
| Linked objects are independent of each other | Linked objects are tightly coupled or dependent on each other |
| if we delete the parent object, the child object will still exist in the system. | if delete the parent object the child object also gets delete . |
| ex: car and tyres are aggregation relationship if we remove tyre also car will function. | ex: folders and files are composition if we delete folder files also get deleted. |
| denoted as empty diamond | denotes as filled diamond |
| weak type of association | Strong type of association |
All basic level question for java covered in this section for any one either experienced or fresher
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All multi-threading level questions such as thread ,process,synchronization ,join,thread priorities covered.
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