Why use getters and setters [duplicate]

Question

Possible Duplicate:
Why use getters and setters?

Why use getters and setters?

Answer 1

To limit access to an internal state of an object.

Consider the classic example of a class of geometric shapes. Say, a Circle object. When you set the radius, you may want to automatically calculate the area (which would be a read-only property)

class Circle
{
     float radius;

    public float Radius
    {
        get { return radius; }
        set { radius = value;  area = Math.Pi * radius * radius;}
    }

    float area;
    float Area
    {
        get { return area;}
    }
}

If you allowed direct access to the "radius" data member, you could not update area when it changed. Further, if you allowed direct access to area, users could change it willy-nilly without regard for radius.

Answer 2

To encapsulate, and that way you make how you store data within your class an implementation detail. If your class has a getter/setter:

private string _mystring = string.Empty;
public string SomeValue
{
 get
 {
   return _mystring;
 }
}

That allows you to change how you manage "SomeValue" in the future. For example, you may decide that rather than storing it in a string, it's actually going to be a Guid under the hood. Now you could go for:

private Guid _myguid= Guid.NewGuid();
public string SomeValue
{
 get
 {
   return _myguid.ToString();
 }
}

Anywhere that your class is used and the "SomeValue" property is accessed will remain unbroken this way.

Validation

You can also validate the value passed in as well, so in another example:

private string _mystring = "My Value";
public string SomeValue
{
 get
 {
   return _mystring;
 }
 set
 {
   if (string.IsNullOrEmpty(value))
   {
     throw new InvalidArgumentException();
   }
   else
   {
     _myString = value;
   }
 }
}

To ensure that the stored string is never set to a null/empty string