Encapsulation in java

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What is Encapsulation in Java?
Encapsulation defines as the wrapping up of data into a single unit. It is the mechanism that binds code and data together which it manipulates. Also we can think about encapsulation as it a protective shield that protects the data from being accessed by the outside of this protected area.
In encapsulation variables or data of a class is hidden from any other class and can be accessed only through any member functions of own class in which they are declared.
In encapsulation data is hidden from other classes, so it is also known as data-hiding.
In java encapsulation can be achieved by making all the variables private and by writing public methods in the class to get and set the values of variables which is declared as private.
Java Bean class the best example of a fully encapsulated class.

What is Advantages of Encapsulation in Java?
Data Hiding: The user will have no idea about inner implementation of the class and it will not be visible to users that how the class is storing the values in the variables. They only knows only we are passing the values to setter methods and variables get initialized with that values.

Increase flexibility: We can make the variables of the class as read only or write only depend on requirement. We can make variables read only by omit setter methods, if we want to make variables write-only then we need to omit getter methods.

Re-usability: Encapsulation also improves the reusability and easy to change with new requirements.

Testing code is easy: Encapsulated code is easy to test for unit testing.
Other advantages it provide the control over the data, suppose we want to set the value of id which should be greater than 100 only we can write the login inside the setter method.   

A simple example of program to demonstrate encapsulation
public class MyClass {

//here variables are declared as private and
//these variables can only be accessed by public methods of class
         private String name;
         private int passport_no;
         private int age;
        
         //get method for name to access
           public String getName() {
                return name;
           }
      
           //set method for name to access
           public void setName(String name) {
                this.name = name;
           }

           //get method for passport_no to access
           public int getPassport_no() {
                return passport_no;
           }

           //set method for passport_no to access
           public void setPassport_no(int passport_no) {
                this.passport_no = passport_no;
           }
    
           //get method for age to access
           public int getAge() {
                return age;
           }
 
           //set method for age to access
           public void setAge(int age) {
                this.age = age;
           }
          
}

In the above example in MyClass all the variables i.e., name,passpoer_no and age are declared as private to achieve encapsulation. The get methods like getName(),getPassport_no()  and getAge() are aet as public ans these methods are used to access private variables. The set methods like setName(), setPassport_no() and setAge() are also public and used to access these variables to set the values of the variables.
Now the program to access the variables of the MyClass class is shown below.
public class TestMain {

     public static void main(String[] args) {
       MyClass obj=new MyClass();
       //setting the values to variables
       obj.setName("'The Tech Matin'");
       obj.setPassport_no(123);
       obj.setAge(23);
                    
       //getting the values
       String name=obj.getName();
       int passport_no=obj.getPassport_no();
       int age=obj.getAge();
       System.out.println(name+" "+passport_no+" "+age);

       //obj.name;//error
//if try to direct access to name then we will get compile time error saying
//The field MyClass.name is not visible       
     }
}
Output:
'The Tech Matin' 123 23

Example of Read Only Class
public class MyClass{
//private college name
private String college="Elphinstone College";
//getter method to access
public String getCollege() {
           return college;
     }
}
Now we can not change the value of college.

Example of Write Only Class
public class MyClass{
//private college name
private String college="Elphinstone College";
//setter method
public void setCollege(String college) {
           this.college = college;
     }
}
Now we can not get the value of college.

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