> For AI agents: the complete documentation index is available at https://nhanbe.id.vn/llms.txt, the full documentation bundle is available at https://nhanbe.id.vn/llms-full.txt.

# Strategy

## Overview

Define a family of algorithms and make them interchangeable.

## When to use

- You need runtime selection of behavior.
- You want to avoid large switch statements.

## Java example

```java
interface PricingStrategy {
    int price(int base);
}

class DiscountStrategy implements PricingStrategy {
    public int price(int base) { return base - 10; }
}

class PricingService {
    private PricingStrategy strategy;
    PricingService(PricingStrategy strategy) { this.strategy = strategy; }
    int compute(int base) { return strategy.price(base); }
}
```

## TypeScript example

```ts
type PricingStrategy = (base: number) => number;

const discount: PricingStrategy = (base) => base - 10;

class PricingService {
  constructor(private strategy: PricingStrategy) {}
  compute(base: number): number { return this.strategy(base); }
}
```

## Pros and cons

Pros:

- Replaces complex conditional logic.
- Easy to add new strategies.

Cons:

- More classes or functions to manage.
- Clients must choose a strategy.

## Common pitfalls

- Strategies with overlapping responsibilities.
- Hard-coded strategy selection in many places.

## Related patterns

- [State](https://nhanbe.id.vn/design-patterns/behavioral/state.md)
- [Decorator](https://nhanbe.id.vn/design-patterns/structural/decorator.md)