Deallocated instance and nil object in objective-c-Collection of common programming errors

Coming from a java background, where everything goes under null pointer exception, I found some difficulties in understanding the difference between nil and deallocated instance in objective-c.

In objective-c it is known that sending a message to a nil object is not sorting any effect to the program flow.

However, sending a message to a deallocated object result in message to deallocated instance error.

In my ideal world a deallocated instance is ‘nil’, but obviously is not.

The precise question are:

• what happens to the object when it is deallocated ?
• If the object is deallocated, shouldn’t it be freed, and then become nil ?