what is the meaning of data hiding

Question

One of the most important aspects of OOP is data hiding. Can somebody explain using a simple piece of code what data hiding is exactly and why we need it?

Answer 1

By data hiding you are presumably referring to encapsulation. Encapsulation is defined by wikipedia as follows:

Encapsulation conceals the functional details of a class from objects that send messages to it.

To explain a bit further, when you design a class you can design public and private members. The class exposes its public members to other code in the program, but only the code written in the class can access the private members.

In this way a class exposes a public interface but can hide the implementation of that interface, which can include hiding how the data that the class holds is implemented.

Here is an example of a simple mathematical angle class that exposes values for both degrees and radians, but the actual storage format of the data is hidden and can be changed in the future without breaking the rest of the program.

public class Angle
{

   private double _angleInDegrees;

   public double Degrees
   {
      get 
      {
          return _angleInDegrees;
      }
      set
      {
          _angleInDegrees = value;
      }
   }

   public double Radians
   {
      get
      {   
          return _angleInDegrees * PI / 180;
      }
      set
      {
          _angleInDegrees = value * 180 / PI;
      }
   }
}