This class represents a handle on a stack of activities.
It should only be used for suspending and resuming the
The activity at the top of the stack is the current activity.
true if the two objects are the same,
Although users won't typically care what the underlying implementation
of a context is, they will need to do comparisons.
So, although this method is provided by Java.Object we have it here
to ensure that we don't forget to implement it!