It is behavioural design pattern. This pattern is also referred as Policy pattern.
This pattern lets us define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
This pattern is useful to when there are different algorithms to choose at runtime depending upon user selection/context.
Same behaviour(end result) however different ways to achieve it.
Real world analogy:
Consider example of project management.
To achieve this, there are different strategies/methodologies to choose from. However, main behaviour/end goal is better project management.
There could be various strategies like Scrum, Kanban, Lean,Waterfall and many more.
Example in software/apps development:
Consider scenario of Payment processing within mobile application.
We can infer that there is one behaviour payment that needs to be achieved. However, there are multiple ways/payment mechanisms to complete payment.
For example, payment can be done using CreditCard , DebitCard or any other mobile wallet APIs. Ultimate goal is to pay specific amount in a specified currency.
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Benefits:
More isolated, understandable and readable code.
Adherence to Open/Closed principle.
Changing algorithms/strategies at runtime is easy.
Drawbacks:
There could be possibility of increased distinct strategies over the period of time and apparently cumbersome to handle/manage them all.
Clients must understand all strategies to properly utilised one over another at runtime.
Comparison with Template method pattern:
Template method depends upon single algorithm in abstract super class and allowing concrete subclasses to override part of steps.
However, Strategy design pattern enables selection of algorithm at runtime. Different strategy is applied to object at runtime to achieve its specific behaviour.
