11.策略模式

约 243 字小于 1 分钟

2026-02-27

策略模式（Strategy Pattern）的主要目的是把一组可替换算法封装为独立策略对象，并在运行时按需切换

适合使用策略模式的场景

同一业务有多套计算规则（折扣、运费、风控等）
希望减少大量 if/else 或 switch 分支
需要在运行时动态切换算法
希望新增策略时不修改已有核心流程

策略接口与具体策略

interface ShippingStrategy {
    calc(weight: number): number;
}

class NormalShipping implements ShippingStrategy {
    calc(weight: number): number {
        return 8 + weight * 2;
    }
}

class ExpressShipping implements ShippingStrategy {
    calc(weight: number): number {
        return 15 + weight * 3;
    }
}

class FreeShipping implements ShippingStrategy {
    calc(): number {
        return 0;
    }
}

上下文类

class ShippingContext {
    constructor(private strategy: ShippingStrategy) {}

    setStrategy(strategy: ShippingStrategy): void {
        this.strategy = strategy;
    }

    calc(weight: number): number {
        return this.strategy.calc(weight);
    }
}

使用示例

const context = new ShippingContext(new NormalShipping());
console.log("普通运费:", context.calc(2));

context.setStrategy(new ExpressShipping());
console.log("加急运费:", context.calc(2));

context.setStrategy(new FreeShipping());
console.log("免运费:", context.calc(2));