Java

Encapsulation,Advantages of using Encapsulation,Implementation of Encapsulation using java

noreply@blogger.com (BUJJJI GADU made in kavali) — Sat, 09 Nov 2013 02:44:00 +0000

Encapsulation

Binding (or wrapping) code and data together into a single unit is known as encapsulation.

For example: A java class is the example of encapsulation.

Java bean is the fully encapsulated class because all the data members are private here.

Encapsulation is the technique of making the fields in a class private and providing access to the fields via public methods. If a field is declared private, it cannot be accessed by anyone outside the class, thereby hiding the fields within the class. For this reason, encapsulation is also referred to as data hiding.

Encapsulation is the ability to package data, related behavior in an object bundle and control/restrict access to them (both data and function) from other objects. It is all about packaging related stuff together and hide them from external elements.

We can see that keywords encapsulation and data hiding are used synonymously everywhere. It should not be misunderstood that encapsulation is all about data hiding only. When we say encapsulation, emphasis should be on grouping or packaging or bundling related data and behavior together.
Encapsulation can be described as a protective barrier that prevents the code and data being randomly accessed by other code defined outside the class. Access to the data and code is tightly controlled by an interface.

Advantages of using Encapsulation :

The ability to modify our implemented code without breaking the code of others who use our code.
It gives maintainability, flexibility and extensibility to our code.
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.
The users of a class do not know how the class stores its data. A class can change the data type of a field and users of the class do not need to change any of their code.

Note :- The public methods are the access points to this class' fields from the outside java world. 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.

Implementation of Encapsulation :


                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;
                      }
                }

Save the above code in a different file like "EncapTest.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());
                 }
            }

Save the above code in a different file like "RunEncap.java" If we Execute this Program it will gives the output as follows : " James 20"

Abstraction,implementation of Abstraction, Use of Abstraction in java

noreply@blogger.com (BUJJJI GADU made in kavali) — Tue, 05 Nov 2013 07:08:00 +0000

Abstraction refers to the ability to make a class abstract in OOP. An abstract class is one that cannot be instantiated. All other functionality of the class still exists, and its fields, methods, and constructors are all accessed in the same manner. You just cannot create an instance of the abstract class. If a class is abstract and cannot be instantiated, the class does not have much use unless it is subclass. This is typically how abstract classes come about during the design phase. A parent class contains the common functionality of a collection of child classes, but the parent class itself is too abstract to be used on its own.
Abstract Class: Use the abstract keyword to declare a class abstract. The keyword appears in the class declaration somewhere before the class keyword.


    
 /* File name : Employee.java */
public abstract class Employee
{
   private String name;
   private String address;
   private int number;
   public Employee(String name, String address, int number)
   {
      System.out.println("Constructing an Employee");
      this.name = name;
      this.address = address;
      this.number = number;
   }
   public double computePay()
   {
     System.out.println("Inside Employee computePay");
     return 0.0;
   }
   public void mailCheck()
   {
      System.out.println("Mailing a check to " + this.name
       + " " + this.address);
   }
   public String toString()
   {
      return name + " " + address + " " + number;
   }
   public String getName()
   {
      return name;
   }
   public String getAddress()
   {
      return address;
   }
   public void setAddress(String newAddress)
   {
      address = newAddress;
   }
   public int getNumber()
   {
     return number;
   }
}
code here, escape it yourself.

Notice that nothing is different in this Employee class. The class is now abstract, but it still has three fields, seven methods, and one constructor. Now if you would try as follows: code here, escape it yourself.


/* File name : AbstractDemo.java */
public class AbstractDemo
{
   public static void main(String [] args)
   {
      /* Following is not allowed and would raise error */
      Employee e = new Employee("George W.", "Houston, TX", 43);

      System.out.println("\n Call mailCheck using Employee reference--");
      e.mailCheck();
    }
}

When you would compile above class then you would get the following error: Employee.java:46: Employee is abstract; cannot be instantiated Employee e = new Employee("George W.", "Houston, TX", 43); ^ 1 error Extending Abstract Class: We can extend Employee class in normal way as follows:


/* File name : Salary.java */
public class Salary extends Employee
{
   private double salary; //Annual salary
   public Salary(String name, String address, int number, double
      salary)
   {
       super(name, address, number);
       setSalary(salary);
   }
   public void mailCheck()
   {
       System.out.println("Within mailCheck of Salary class ");
       System.out.println("Mailing check to " + getName()
       + " with salary " + salary);
   }
   public double getSalary()
   {
       return salary;
   }
   public void setSalary(double newSalary)
   {
       if(newSalary >= 0.0)
       {
          salary = newSalary;
       }
   }
   public double computePay()
   {
      System.out.println("Computing salary pay for " + getName());
      return salary/52;
   }
}

Here, we cannot instantiate a new Employee, but if we instantiate a new Salary object, the Salary object will inherit the three fields and seven methods from Employee.


/* File name : AbstractDemo.java */
public class AbstractDemo
{
   public static void main(String [] args)
   {
      Salary s = new Salary("Mohd Mohtashim", "Ambehta, UP", 3, 3600.00);
      Employee e = new Salary("John Adams", "Boston, MA", 2, 2400.00);

      System.out.println("Call mailCheck using Salary reference --");
      s.mailCheck();

      System.out.println("\n Call mailCheck using Employee reference--");
      e.mailCheck();
    }
}

This would produce the following result: Constructing an Employee Constructing an Employee Call mailCheck using Salary reference -- Within mailCheck of Salary class Mailing check to Mohd Mohtashim with salary 3600.0 Call mailCheck using Employee reference-- Within mailCheck of Salary class Mailing check to John Adams with salary 2400. Abstract Methods: If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as abstract. The abstract keyword is also used to declare a method as abstract. An abstract method consists of a method signature, but no method body. Abstract method would have no definition, and its signature is followed by a semicolon, not curly braces as follows:


public abstract class Employee
{
   private String name;
   private String address;
   private int number;
   
   public abstract double computePay();
   
   //Remainder of class definition
}

Declaring a method as abstract has two results: The class must also be declared abstract. If a class contains an abstract method, the class must be abstract as well. Any child class must either override the abstract method or declare itself abstract. A child class that inherits an abstract method must override it. If they do not, they must be abstract and any of their children must override it. Eventually, a descendant class has to implement the abstract method; otherwise, you would have a hierarchy of abstract classes that cannot be instantiated. If Salary is extending Employee class, then it is required to implement computePay() method as follows:


/* File name : Salary.java */
public class Salary extends Employee
{
   private double salary; // Annual salary
  
   public double computePay()
   {
      System.out.println("Computing salary pay for " + getName());
      return salary/52;
   }

   //Remainder of class definition
}

Java Object Oriented Programming Language , OOP's in java,java with OOP's,Advantages of OOP's,Object Oriented Programming Language

noreply@blogger.com (BUJJJI GADU made in kavali) — Mon, 04 Nov 2013 10:17:00 +0000

Abstraction : Hiding unnecessary data from user is called Abstraction access specifiers like public,private etc are used to provide different level in abstraction. Implementation of Abstractioon is as follows

Encapsulation : Taking data and object in a single unity is called Encapsulation.A class is example for Encapsulation. Implementation of Encapsulation

Inheritance : creating anew class from existing class is called Inheritance.reusability is main advantage in inheritance.

Polymorphism : if single mthod performs different task is called polymorphism. Abstraction Hiding unnecessary things and showing the essential information.
Example: Suppose take a car: In that we will have breaks and stering and etc... Here when we are changing the gear box to up or bottom then gears will work but we don't know how they are managing internally and we don't no how it is working. As a driver we don't need to know how it is working internally when we are changing every time. That is the reason they will hide the wires and cables internally and they will show up only gear box to us.

Advantages: 1) Code will be clean and for managing it will be very easy Inheritance Acquiring the properties from super class to subclass.

Example: Suppose take two java classes Class A contains 2 variables and ClassB Extends Class A that means here ClassB can access the classA variables without declaring it. If we do this then the memory will be less and reusable.

Advantages: 1)Reusability of code Encapsulation Wrapping up of data and methods into a single unit. Example: In our class we need to make all our varables and methods keeping together.

Advantage: Maintance will be good Polymorphism It means many forms. 2 types:
1) Compile time polymorphism
2) Run time polymorphism Method overloading is an example for Compile time polymorphism and Method overriding is an example for Run time polymorphism