Law of Demeter in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Law of Demeter?

The Law of Demeter is a design guideline that suggests a module should only communicate with its immediate friends and not with strangers. It means an object should only call methods of: itself, its fields, parameters, or objects it creates.

beginner

Why is the Law of Demeter important in system design?

It reduces dependencies between modules, making the system easier to maintain and less fragile. Changes in one part of the system are less likely to break others.

intermediate

Which of the following violates the Law of Demeter?<br>

order.getCustomer().getAddress().getCity()

This violates the Law of Demeter because it accesses a chain of objects beyond immediate friends. The object should not reach through multiple objects to get data.

intermediate

How can you fix a violation of the Law of Demeter?

You can add methods to intermediate objects to hide internal structure. For example, add a method getCity() in Customer that returns the city, so callers don't chain calls.

beginner

What is a real-life analogy for the Law of Demeter?

Imagine you want to know the weather. Instead of asking your friend’s friend’s friend, you ask your friend directly. Your friend then asks their friend and tells you the answer. You don’t talk to strangers.

Which of these is a principle of the Law of Demeter?

A Use global variables for communication

B Access any object in the system freely

C Talk only to your immediate friends

D Chain multiple method calls across objects

The Law of Demeter advises to only communicate with immediate friends (directly related objects).

What problem does the Law of Demeter help to avoid?

A Low performance

B High coupling between modules

C Memory leaks

D Syntax errors

It reduces tight coupling by limiting object interactions.

Which code snippet violates the Law of Demeter?

A user.getProfile().getEmail()

B user.sendMessage()

C order.calculateTotal()

D cart.addItem(item)

Calling getEmail() on the profile object returned by getProfile() is chaining calls beyond immediate friends.

How can you improve code that violates the Law of Demeter?

A Add methods to hide internal object details

B Increase the number of chained calls

C Use global variables instead

D Remove all method calls

Adding methods to intermediate objects encapsulates details and prevents chaining.

The Law of Demeter is also known as:

A Don't Repeat Yourself

B Open/Closed Principle

C Single Responsibility Principle

D Principle of Least Knowledge

The Law of Demeter is often called the Principle of Least Knowledge.

Explain the Law of Demeter and why it is useful in designing software systems.

Think about how objects should limit their knowledge about others.

Describe a scenario where violating the Law of Demeter causes problems and how you would refactor it.

Consider how to hide internal object structure.