Important Basic Concepts

1) what is encapsulation ?
Encapsulation JAVA's PIE (polymorphosim, Inheritance, Encapsulation) concept, to protect the data.

What is protection of data in encapsulation?
 Class person {
       int salary;
       // getters
       public void setSalary(int salary) {
             if(salary < 0) {
                  //throw exception
             }
       }
}
person p = new person();
p.setSalary(10000);

But you are creating the person p object, through p object you are setting the value of salary, But how are you protecting data here ?

While entering the salary data, in the setSalary method we had put some constraints of not allowing the < 0 values, we are protecting the salary allows only integer values > 0.

2) Inside enum class why can't declare abstract methods ?
enum Biryani {
    abstract void recipes() ;
}
1) if you declare any abstract method, then you will make class also abstract. these abstract method implemented by child class

*** Any child class can't extend enum class, because enum class is final.
       enum class final, final and abstract combination will not work.

*** Inside enum only instance and static methods not abstract methods.

3) Difference between enum, Enum, Enumeration ?
enum: enum type just like class type. defined group of named constants.
class ramesh {
},

enum ramesh {
}

Enum: It's a class present in java.lang package which act as a base class for all java enums

Enumeration: It's an interface in java.lang, which can be used for retrieving objects
from collection one by one