CODEWITHSUNDEEP
oopsoftware-design
Mark White
Mark White

Reputation: 41

OOP , object concept

According to the standard definition, an object is an entity that contains both data and behaviour. According to my understanding the data is sent from outside.For eg,we have a class that computes the square of a number.We create an instance and sends a message,along with the number, to the object to compute the square,. Are we not sending the data from outside? Why do all the definitions state that the object contains the data? Thanks

Upvotes: 3

Views: 155

Answers (4)

Nazar Merza
Nazar Merza

Reputation: 3454

Data, in this context, is state of the object. The definition says that the state/data of object should be internally stored. For example, consider the following class:

class Math {

  Double square(double x) {
      return x * x;
  }
  // other similar functions
}

As a language construct, it is a class. But, it is not a true class in object-oriented sense. Because it does not have a state or data. It is just a function wrapped in a class construct. This is not necessarily wrong. Because in this case, it happens that you have operations that don't need a state.

What the definition trying to emphasize is that: you have a real object, when it (or it's class) has both data and behavior. Not every usage of the class construct represents a true object.

Therefore, you have an object if the class representing it satisfies the following three conditions.

  1. The class has state/date. If not, then it is just a bunch of functions. It is not object-oriented, it is procedural.
  2. The class has behavior. If not, then it is just a container, a bunch of variable ( Structures in C).
  3. Not only the class has state/data and behavior/methods, but there is an intrinsic relation between the data and behavior. Which means that just throwing some variables and functions together does not make a true object. For example, if you have state/data and you also have some method, in the class, but if that function does not need to operate upon any of the state, then there is a question whether that method really belongs to that class.

Below is a simple example of what I think is a proper class (representation of object).

Class Patient {
      // blood pressure
     double systolic;
     double diastolic;
     double weight;
      int age;
     public Patient(double systolic,   double diastolic,  double weight, int age){

    }

   Public boolean isHealthy(){
        // do some calculations and algorithms on age, weight and blood pressure indicators.
        // return result as true of false
  }

}

Here, we see that class has both state and behavior. We also see that both state and behavior really belong to this class. They are properties of the concept of patient. We further see that operation has an intrinsic relation to data. You can’t decide whether the patient is healthy or not, without consulting/using its state.

Upvotes: 3

Amir
Amir

Reputation: 4111

An object is an instance of a class.

Class (a, a*a) is square class but (2, 4) is an instance of it (object). Yes, data is sent to the class and creates new object.

Upvotes: 0

SomeWittyUsername
SomeWittyUsername

Reputation: 18368

Your example is a private case where the object doesn't need to hold data (i.e. state). In this case it can be replaced with a function (just the behavior). Most objects need to store data. E.g., an object Person should contain the qualities describing the person, not just possible behavior.

Upvotes: 0

Andrea Sindico
Andrea Sindico

Reputation: 7440

I think the problem is with your example which badly fit with an Object Oriented design. I just mean that computing the square of a number is a memoryless function thus there is obviously no reason to store data inside the object properties. However when you will have to deal with the management of stateful entities you will get more easily the importance of classes and object orientation in general.

Upvotes: 1

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