Strategy Pattern

Strategy Pattern

What is it?

Design pattern that lets you define a family of methods

that are interchangeable at runtime

What problem does it solve?

Introduce new behaviours without violating the

Open-Closed principle

When should we use this pattern?

When we need multiple ways of achieving the same task

Strategy Pattern

Strategy Pattern

Currently, the code uses switch statements to handle each of the different cases.

How does the code violate the open/closed principle?

Strategy Pattern

Currently, the code uses switch statements to handle each of the different cases.

How does the code violate the open/closed principle?

• Not closed for modification / open for extension.
• Each new case requires a new switch statement.

Let's refactor it!

Strategy Pattern

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Observer Pattern

Observer Pattern

What is it?

Define a subscription mechanism that notifies observers
about any event that happens to the subject that they
are observing

What problem does it solve?

Modelling a n-to-many relationship may be difficult. If
not done well, it typically leads to tight coupling

When should we use this pattern?

If there is a state that multiple observers are interested in

Observer Pattern

Observer Pattern

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State Pattern

State Pattern

What is it?

Behavioural design pattern that allows an object to alter its behaviour when its internal state changes.

When should we use this pattern?

• Behaviour differs depending on the current state
• Be able to switch behaviour at runtime

State Pattern

Text

• Player has methods that can change its state
• Behaviour of Player changes based on its state
  • Music is played in the PlayingState 
  • Music is paused in the ReadyState

State Pattern

State Pattern

Find out more at State (refactoring.guru)