The Law of Demeter (LoD) is a design guideline for developing software that promotes loose coupling between units. It was originally proposed in 1987 at Northeastern University as part of the Demeter Project. The LoD principle states that a unit should only be aware of and interact with its immediate friends and not with other distant units. Following the LoD can make software more maintainable, adaptable, and less dependent, though it may increase code size and overhead in some cases. Examples are provided to illustrate proper and improper implementations of the LoD.

1. by Ismael Soares
@rkmael
Law of Demeter

2. What’s it?
The
Law
of
Demeter
(LoD)
or
principle
of
least
knowledge
is
a
design
guideline
for
developing
software
(https://en.wikipedia.org/wiki/Law_of_Demeter)

3. The Origin
The
guideline
was
proposed
at
Northeastern
University
towards
the
end
of
1987

4. Demeter is not a man,
is a Greek goddess!
It
is
so
named
for
its
origin
in
the
Demeter
Project,
an
adaptive
programming
and
aspect-­‐oriented
programming
effort.
It means a philosophy of bottom-up

5. LoD Principle:
• Each
unit
should
have
only
limited
knowledge
about
other
units:
only
units
"closely"
related
to
the
current
unit.
• Each
unit
should
only
talk
to
its
friends;
don't
talk
to
strangers.
• Only
talk
to
your
immediate
friends.

6. Advantages:
• More
maintainable
• More
adaptable
• Less
dependence
• Very
useful
in
layered
architecture

7. Disadvantages:
• More
code
• In
some
cases,
this
can
add
noticeable
time
and
space
overhead

9. Bad Example
Fonte: https://www.javacodegeeks.com/2012/06/demeter-law.html

10. Good Example

14. Obrigado
@rkmael
rkmael@hotmail.com
rkmael.com