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The key advantage of using an Object Oriented Programming language like Java is that it provides your code - security, flexibility and its easy maintainability through encapsulation.

Why encapsulation?

• Encapsulation helps us in binding the data(instance variables) and the member functions(that work on the instance variables) of a class.


• Encapsulation hides the data(instance variables) of a class from an illegal direct access.


• It also helps us to make a flexible code which is easy to change and maintain.


• The ability to modify your code, without affecting the code of others who used your code, is another key use of encapsulation.

Let's understand the need of encapsulation, by first seeing a class that is an example of a bad encapsulation and the drawbacks associated with it.

An example of a bad encapsulation.

We are creating a class with a public instance variable, that should never be set to a negative value.

class Stats
{
public int  weight; //weight with public access, can be accessed by anyone 

public static void main(String... ar)
{
Stats ob = new Stats();
ob.weight = -100; //weight set to a negative value, legal but wrong.
}

}

In this code, we have made a class Stats with its public instance variables, weight. In the main method, we have created an object of this class and through it we have directly accessed its public instance variable to set it to a negative value i.e. ob.weight=-100, which will cause a problem as weight is never a negative value.

Drawbacks of a bad encapsulation.

Giving a public access to instance variable of your class makes it unsafe from an unauthorized access, hence, anyone can directly access it directly through class's object and set its value even beyond its permissible range, which may cause an issue.

Now in order to rectify this issue, if you modify the access modifier of instance variable, weight, to private, you will end up breaking the code of everyone who are already inheriting your Stats class and are directly accessing its instance variable, weight. Thus such code is not only less secure but also less flexible to change.

Hence, you should only create your classes by following proper encapsulation. Let's see how encapsulation comes to the rescue.

Rules to encapsulation are -



• Keep the access modifiers of instance variables of a class to private or protected.


• Enforce calling public getter, setter methods of the class in order to get or set the value of instance variables of the class.


• Use the JavaBeans naming convention of getters and setters methods for class methods.

An example of good encapsulation

class Stats
{
private int  weight;



public getWeight()  //Getter method to get weight.
{
return weight;
}



public void setWeight(int wt)  //Setter method to set weight.
{
if(w<0)
	System.out.println("Please enter weight greater than zero");

else
	weight=w;
}


public static void main(String... ar)
{
Stats ob= new Stats();
ob.setWeight(100);
}

}

In this code, we have restricted the access to weight instance variable by declaring it private, hence, anyone wishing to set the value of weight instance variable, will have to call setWeight() method. In setWeight() method we have an if-else condition that makes sure that instance variable, weight's value should not be set to a negative value.

Following such proper encapsulation also provides flexibility to your code, allowing you to make changes to you code, without breaking the code of others who were accessing your code, for example- tomorrow, you may decide to put in a different if-else condition, like - weight should be set between 50 and 100 kg/pounds. Modifying your code in such way will not affect anyone accessing your class.

Benefits of encapsulation

Through such proper Encapsulation, now your code is more flexible to the change, easy to maintain and you've also secured and protected your data(instance variables) from the direct access by giving it a private access.

Difference between encapsulation and abstraction

While encapsulation helps in hiding the data(instance variables) of a class from an illegal access, abstraction provides essential general features without providing implementation details, by using an abstract class or an interface.


Example of Abstraction

• interface food
  {
  public void cook();
  }


We have created an interface Food and we have also provided the method signature of its method cook() and it's left upon the implementer of this interface to provide implementation of method cook() as he/she likes.





• class Soup implements Food
  {
  public void cook()
  {
  System.out.println("Cooking Soup");
  }
  }


A class Spaghetti implements interface Food by providing implementation of its method cook().





• class Pasta implements Food
  {
  public void cook()
  {
  System.out.println("Cooking Pasta");
  }
  }


class Pasta implements interface Food and providing implementation of its method cook() as it likes.





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