Do I need to implement a dispose or finalize in my objects?

Question

For too long I let the garbage collector do its magic, removing all responsibilities from my self.

Sadly it never turned into an issue... So I never gave a second thought to the subject.

Now when I think about it I don't really understand what the "dispose" function really does and how and when it should be implemented.

The same question for finalize...

And a last question... I have a class pictureManipulation : when I need to save/resize/change format ... I start a new instance of that class use its objects and... well let the garbage collection kill the instance

class student
{
   public void displayStudentPic()
   {
      PictureManipulation pm = new PictureManipulation();
      this.studentPic = pm.loadStudentImage(id); 
   }
}

Class Test
{
  student a = new Student();
  a.displayStudentPic();
  // Now the function execution is ended... does the pm object is dead? Will the GC will kill it?
}

Answer 1

Regarding your class Student

Do I need a Dispose() ?

Assuming the Picture class is IDisposable: Yes. Because a Student object 'owns' the studentPic and that makes it responsible for cleaning it up. A minimal implementation:

class Student : IDisposable
{
   private PictureClass studentPic;
   public void Dispose()
   {
      if (studentPic != null)
        studentPic.Dispose();
   }
   ...
}

And you now use a Student object like:

void Test
{
  using (Student a = new Student())
  {
     a.displayStudentPic();    
  } // auto Dispose by using() 
}

If you can't/don't use a using(){} block, simply call a.Dispose(); when you're done with it.

But please note that the (far) better design here would be to avoid keeping a picture object inside your Student object. That sets off a whole chain of responsibilities.

Do I need a Finalizer?

No. Because when a Student object is being collected, its studentPic object is guaranteed to be collected in the same run. A Finalizer (destructor) would be pointless but still expensive.