Important Java Interview Questions - Part 7

I'm sharing my experience with you as these are the questions which have been asked to me while interviewing on java profile.

Where have u used abstraction and encapsulation in your project?

We use encapsulation everywhere in java like when we create a class in java we are using encapsulation. Abstraction we use when we create abstract class or interface using abstraction in java.

"Encapsulation is to hide the variables or something inside a class, preventing unauthorized parties to use. So the public methods like getter and setter access it and the other classes call these methods for accessing"

Using Encapsulation we achieve “Data Hiding, Information Hiding” in java. Encapsulation binds data (attributes and methods) and the code in the form of a class. Encapsulation is the technique of making the fields in a class private and providing access to the fields via public methods. Encapsulation provides “access control” through which we can control the access of class in accessing methods or members of class.

Abstraction on the other hand, can be explained as the capability to use the same interface for different objects. It involves the facility to define objects that represent abstract "actors" that can perform work, report on and change their state, and "communicate" with other objects in the system. Different implementations of the same interface can exist. Details are hidden by encapsulation.

                                                                

Explanation with live example:

Encapsulation

Function of button is to start the functioning of machine but did you ever think that what happens inside machine when button was pressed like inside mechanism of machine. Actually we do not need to worry about that internal functionality of washing machine till the time our machine is working fine that is called encapsulation. You don’t "need to know the internal working of the washing machine to operate" with it. You have an interface to use the device behavior without knowing implementation details.

Abstraction 

To explain you about abstraction in java we can take three different entities (People in real world).

You: As a user you know how to start a washing machine. We just need to press a button and all other operations behind the scene are happening and are abstracted from user.

Now you are facing some problem with your machine when you are pressing start button it is not turning on there might be some major issue with your hardware which needs to be corrected. Then you call local mechanic to check the problem.

Local Mechanic: Our local mechanic knows some of the implementations of starting machine. He can open machine and check some wires and connections etc which means Local Mechanic knows some of the implementations of machine.

Now the situation arrived where we have to call washing machine manufacturing company service center and ask them for service of machine. They will send an expert to check the problem.

Expert: Since our expert (Designer of the machine) mechanic knows all the operations of our machine, he we repair it fast and will give you resolution of your problem. So in short Expert Entity knows all the implementations of the machine.

The machine's operation is completely abstracted from you and it is partially implemented to Local Mechanic and fully implemented to Expert. So you are an abstract class having only abstract methods, Local Mechanic has extended You(Since he is also an ordinary user) and he implemented some of the methods and last our expert extending Local Mechanic and implementing all the methods.

Also in terms of complexity "Whenever abstraction decreases, complexity increases"(Since our Expert Entity has very less abstraction, his complexity of work also increases)

In Java, garbage collection is also a best example for explaining abstraction.

If you still have any question you can reach me any time through email (jigyasu2010@hotmail.com)