<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
a	O
poltergeist	B-General_Concept
(	O
or	O
gypsy	O
wagon	O
)	O
is	O
a	O
short-lived	O
,	O
typically	O
stateless	B-Application
object	O
used	O
to	O
perform	O
initialization	O
or	O
to	O
invoke	O
methods	O
in	O
another	O
,	O
more	O
permanent	O
class	O
.	O
</s>
<s>
"	O
As	O
a	O
gypsy	O
wagon	O
or	O
a	O
poltergeist	B-General_Concept
appears	O
and	O
disappears	O
mysteriously	O
,	O
so	O
does	O
this	O
short	O
lived	O
object	O
.	O
</s>
<s>
A	O
poltergeist	B-General_Concept
can	O
often	O
be	O
identified	O
by	O
its	O
name	O
;	O
they	O
are	O
often	O
called	O
"	O
manager_	O
"	O
,	O
"	O
controller_	O
"	O
,	O
"	O
supervisor	O
"	O
,	O
"	O
start_process	O
"	O
,	O
etc	O
.	O
</s>
<s>
Sometimes	O
,	O
poltergeist	B-General_Concept
classes	O
are	O
created	O
because	O
the	O
programmer	B-Application
anticipated	O
the	O
need	O
for	O
a	O
more	O
complex	O
architecture	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
poltergeist	B-General_Concept
arises	O
if	O
the	O
same	O
method	O
acts	O
as	O
both	O
the	O
client	O
and	O
invoker	O
in	O
a	O
command	B-Language
pattern	I-Language
,	O
and	O
the	O
programmer	B-Application
anticipates	O
separating	O
the	O
two	O
phases	O
.	O
</s>
<s>
Poltergeists	B-General_Concept
should	O
not	O
be	O
confused	O
with	O
long-lived	O
,	O
state-bearing	O
objects	O
of	O
a	O
pattern	O
such	O
as	O
model	O
–	O
view	O
–	O
controller	O
,	O
or	O
tier-separating	O
patterns	O
such	O
as	O
business-delegate	O
.	O
</s>
<s>
To	O
remove	O
a	O
poltergeist	B-General_Concept
,	O
delete	O
the	O
class	O
and	O
insert	O
its	O
functionality	O
in	O
the	O
invoked	O
class	O
,	O
possibly	O
by	O
inheritance	B-Language
or	O
as	O
a	O
mixin	B-Language
.	O
</s>
