Java Reference
In-Depth Information
we have
isTeleporting
and
playerTeleports
to keep track of players and the locations
they've teleported to and from.
We're checking to see if our
isTeleporting
list contains this player already. If it
doesn't, we'll add it—this player has just started teleporting. If the
isTeleporting
list already contains this player, then we should ignore this event (and remove
the player from the list). That means we generated this event ourselves, and
we don't want our own teleport to trigger the teleport, because it would keep
doing that forever. So we throw this extra teleport event out.
If this player has teleported before, we'll get a
locs
from the
playerTeleports
hash
(a hash of locations) using the player as a key. We'll add this location to the
existing list. If this is the player's first time teleporting, we'll make a new list
(of
Location
s) and add this location as its first entry.
But this is no ordinary list. It's a kind of list, all right, but it's a
Stack
, not a
plain list. A
Stack
works like a stack of pancakes. You add to the top of the
stack, and when you remove a pancake it comes off the top of the stack. That's
the model we want for our list of places we've teleported. As you teleport, each
location is added to the top of the stack—and it's the top one you want to go
back to next, then the one under that, and so on.
To add an object to the top of a stack, you
push
it on. To get the value and
remove the object at the top, you
pop
it off. To just check on the top value
without removing it, you can
peek
at it.
As players teleport around, we'll keep a stack of each of their teleport locations,
stored in a
Stack
in our
playerTeleports
variable. We can get to the stack using
the
Player
object as a key. You can see what this looks like
on page 132
.
Finally, we get down to
backCommand
. When we get a
back
command, we'll get
the player's list of teleport locations (if there is one), and peek at the location
on the top of the stack, saving that in
loc
for now.
Maybe we teleported to this spot and haven't moved yet. In that case, we'd
want to go to the previous spot—not stay at this location. So we'll test for
that: if we're still at the same location as the last teleport (or close to it), we'll
remove that location from the
locs
list by using the
pop
, and set
loc
to the next
location in the stack.
Either way, we've got a
loc
pointing to the spot that we want to teleport to.
We'll add the player to the
isTeleporting
list and teleport the player to the new
location.
