Java - Encapsulation

Java Encapsulation

Encapsulation is one of the four fundamental OOP concepts. The other three are inheritance, polymorphism, and abstraction.

Encapsulation in Java is a mechanism of wrapping the data (variables) and code acting on the data (methods) together as a single unit. In encapsulation, the variables of a class will be hidden from other classes, and can be accessed only through the methods of their current class. Therefore, it is also known as data hiding.

Achieving Encapsulation in Java

To achieve encapsulation in Java −

• Declare the variables of a class as private.

• Provide public setter and getter methods to modify and view the variables values.

Java Encapsulation Example

Following is an example that demonstrates how to achieve Encapsulation in Java −

/* File name : EncapTest.java */
public class EncapTest {
   private String name;
   private String idNum;
   private int age;

   public int getAge() {
      return age;
   }

   public String getName() {
      return name;
   }

   public String getIdNum() {
      return idNum;
   }

   public void setAge( int newAge) {
      age = newAge;
   }

   public void setName(String newName) {
      name = newName;
   }

   public void setIdNum( String newId) {
      idNum = newId;
   }
}

The public setXXX() and getXXX() methods are the access points of the instance variables of the EncapTest class. Normally, these methods are referred as getters and setters. Therefore, any class that wants to access the variables should access them through these getters and setters.

The variables of the EncapTest class can be accessed using the following program −

/* File name : RunEncap.java */
public class RunEncap {

   public static void main(String args[]) {
      EncapTest encap = new EncapTest();
      encap.setName("James");
      encap.setAge(20);
      encap.setIdNum("12343ms");

      System.out.print("Name : " + encap.getName() + " Age : " + encap.getAge());
   }
}

public class EncapTest {
   private String name;
   private String idNum;
   private int age;

   public int getAge() {
      return age;
   }

   public String getName() {
      return name;
   }

   public String getIdNum() {
      return idNum;
   }

   public void setAge( int newAge) {
      age = newAge;
   }

   public void setName(String newName) {
      name = newName;
   }

   public void setIdNum( String newId) {
      idNum = newId;
   }
}

Output

Name : James Age : 20

Benefits of Encapsulation

• The fields of a class can be made read-only or write-only.

• A class can have total control over what is stored in its fields.

Java Encapsulation: Read-Only Class

A read-only class can have only getter methods to get the values of the attributes, there should not be any setter method.

Example: Creating Read-Only Class

In this example, we defined a class Person with two getter methods getName() and getAge(). These methods can be used to get the values of attributes declared as private in the class.

// Class "Person"
class Person {
  private String name = "Robert";
  private int age = 21;

  // Getter methods
  public String getName() {
    return this.name;
  }

  public int getAge() {
    return this.age;
  }
}

public class Main {
  public static void main(String args[]) {
    // Object to Person class
    Person per = new Person();

    // Getting and printing the values
    System.out.println("Name of the person is: " + per.getName());
    System.out.println("Age of the person is: " + per.getAge());
  }
}

Output

Name of the person is: Robert
Age of the person is: 21

Java Encapsulation: Write-Only Class

A write-only class can have only setter methods to set the values of the attributes, there should not be any getter method.

Example: Creating Write-Only Class

In this example, we defined a class Person with two setter methods setName() and setAge(). These methods can be used to set the values of attributes declared as private in the class.

// Class "Person"
class Person {
  private String name;
  private int age;

  // Setter Methods
  public void setName(String name) {
    this.name = name;
  }
  public void setAge(int age) {
    this.age = age;
  }
}

public class Main {
  public static void main(String args[]) {
    // Object to Person class
    Person per = new Person();

    // Setting the values
    per.setName("Robert");
    per.setAge(21);
  }
}

Java Encapsulation: More Examples

Example 1: Person Class (Fully Encapsulated)

This example creates a fully encapsulated class named "Person". This class has private class attributes, setter, and getter methods.

// Class "Person"
class Person {
  private String name;
  private int age;

  // Setter Methods
  public void setName(String name) {
    this.name = name;
  }
  public void setAge(int age) {
    this.age = age;
  }

  // Getter methods
  public String getName() {
    return this.name;
  }

  public int getAge() {
    return this.age;
  }
}

// The Main class to test encapsulated class "Person"
public class Main {
  public static void main(String args[]) {
    // Objects to Person class
    Person per1 = new Person();
    Person per2 = new Person();

    // Setting the values
    per1.setName("Robert");
    per1.setAge(21);

    per2.setName("Riyan");
    per2.setAge(22);

    // Printing the values
    System.out.println("Person 1: Name : " + per1.getName() + " Age : " + per1.getAge());
    System.out.println("Person 2: Name : " + per2.getName() + " Age : " + per2.getAge());

  }
}

Output

Person 1: Name : Robert Age : 21
Person 2: Name : Riyan Age : 22

Example 2: Employee Class (Fully Encapsulated)

This example creates a fully encapsulated class named "Employee". This class has private class attributes, setter, and getter methods.

// Class "Employee"
class Employee {
  private String emp_name;
  private String emp_id;
  private double net_salary;

  // Constructor
  public Employee(String emp_name, String emp_id, double net_salary) {
    this.emp_name = emp_name;
    this.emp_id = emp_id;
    this.net_salary = net_salary;
  }

  // Getter methods
  public String getEmpName() {
    return emp_name;
  }

  public String getEmpId() {
    return emp_id;
  }

  public double getSalary() {
    return net_salary;
  }

  // Setter methods
  public void setEmpName(String emp_name) {
    this.emp_name = emp_name;
  }

  public void setEmpId(String emp_id) {
    this.emp_id = emp_id;
  }

  public void setSalary(double net_salary) {
    this.net_salary = net_salary;
  }
}

// The Main class to test encapsulated class "Employee"
public class Main {
  public static void main(String args[]) {
    // Objects to Employee class
    // First object - setting values using constructor
    Employee emp = new Employee("Robert", "EMP001", 75450.00);

    // Printing data
    System.out.println("Employee (Intial Values):");
    System.out.println(emp.getEmpId() + " , " + emp.getEmpName() + " , " + emp.getSalary());

    // Updating values using setter methods
    emp.setEmpName("Riyan");
    emp.setEmpId("EMP002");
    emp.setSalary(90500.00);

    // Printing data
    System.out.println("Employee (Updated Values):");
    System.out.println(emp.getEmpId() + " , " + emp.getEmpName() + " , " + emp.getSalary());
  }
}

Output

Employee (Intial Values):
EMP001 , Robert , 75450.0
Employee (Updated Values):
EMP002 , Riyan , 90500.0