Interface And Abstraction – Spiritual Explanation

“What is the difference between interface and abstract class?”, a typical interview question . Answer is so obvious, and we can list at least 3 differences. Here is an attempt to correlate Object Oriented world with spiritual world, and explain abstraction and interface.

“Soul is an abstract notion realized by concrete living being”. So as per OO world, if you got “Soul” as abstract class, you got to have a concrete class “Life”. Soul can not operate without Life.

Just like I said object is an entity with an objective to live, abstract class can live through concrete class. Inheritance is the only mechanism for an abstract class to live. Spiritually, Soul operates through life. Life is an object with a process thread running in it.

In Spiritual world, it is said that “Soul carries the karma (good or bad actions) from previous life, which has influences in the new life”. If you consider this statement, karma is the action log recorded into the abstract class.

Body is an interface to life (and hence interface to Soul) and real world. so IBody can be implemented by body of human, bird or any living creature. Once the objective is complete in this real world, destructor is called on life object. However actions are kept recorded (like log files) in the abstract class through out this new life.

In every new life actions recorded in abstract class is not revealed, as it is private declaration . Only the ultimate object builder (God)  has access to it. Object builder reads this private variable, and makes the decision of choosing a new interface for Soul. Dispose method is programmed to be called in a timer function. When timer event fires, dispose is called, and the Life object is disposed terminating the process thread.

After thread is terminated and Life is disposed, Object builder reads the record log from Soul class. Based on the karma recorded in the log, a new object with the suitable interface (body) is created, and Life is induced into it with a process thread. And a timer is started in the Life class, which when fires Thread Abort is called.

cpp vs Java : Abstract classes

CPP :
A class that contains at least one pure virtual function is said to be abstract. Because an abstract class contains one or more functions for which there is no definition (that is, a pure virtual function), no objects of an abstract class may be created. Instead, an abstract class constitutes an incomplete type that is used as a foundation for derived classes.
Although you cannot create objects of an abstract class, you can create pointers and references to an abstract class. This allows abstract classes to support run-time polymorphism, which relies upon base-class pointers and references to select the proper virtual function.

Abstract classes vs interfaces

Abstract classes	Interfaces
Abstract classes are used only when there is a “is-a” type of relationship between the classes.	Interfaces can be implemented by classes that are not related to one another.
You cannot extend more than one abstract class.	You can implement more than one interface.
Abstract class can implemented some methods also.	Interfaces can not implement methods.
With abstract classes, you are grabbing away each class’s individuality.	With Interfaces, you are merely extending each class’s functionality.

But in the end a good design only matters. See abstract interfaces.

Abstract-Interface or skeletal implementations

You can combine the virtues of interfaces and abstract classes by providing an abstract skeletal implementation class to go with each nontrivial interface that you export. So abstract class provides basic functionality, but interface adds to it and we get skeletal implementation or abstract-Interface.

Abstract classes

As seen from the previous example, the superclass is more general than its subclass(es). The superclass contains elements and properties common to all of the subclasses. The previous example was of a concrete superclass that instance objects can be created from. Often, the superclass will be set up as an abstract class which does not allow objects of its prototype to be created. In this case, only objects of the subclass are used. To do this the reserved word abstract is included in the class definition.
Abstract methods are methods with no body specification. Subclasses must provide the method statements for their particular meaning. If the method was one provided by the superclass, it would require overriding in each subclass. And if one forgot to override, the applied method statements may be inappropriate.

public abstract class Animal  // class is abstract
{
  private String name;
  public Animal(String nm)      // constructor method
  { name=nm; }
  public String getName()       // regular method
  { return (name); }
  public abstract void speak(); // abstract method - note no {}
}


Abstract classes and methods force prototype standards to be followed (ie. they provide templates).
See also - Abstract classes : cpp vs java