该设计模式如何称呼？ （用地图代替开关） [英] How is this design pattern called? (map instead of switch)

问题描述

所以我们有商品，商品有价格。
我想计算商品价格。

So we have goods and goods have prices. I'd like to calculate the price of goods.

第一个版本（切换）：

int getPrice(String name){
   switch(name){
      case "Apple": return 20;
      case "Banana": return 100;
      ... 
   }
}

第二版（地图）：

Map<String, Integer> prices = new HashMap<String, Integer>;    

int getPrice(String name){
    return prices.get(name);
}

那么该方法（或设计模式）如何调用？

So how this method (or design pattern) is called? Has it a special name?

推荐答案

我会说这是查找表。我不会将其称为设计模式，因为它们更大且更抽象。这是一个实现细节。

I would say this is a special case of a lookup table. I would not call it a design pattern because those are larger and more abstract. This is an implementation detail.

例如，可以将其用于策略模式：

For example this can be used in the strategy pattern:

static KnotStrategy getKnotStrategy(String name) {
    switch(name.toLowerCase()) {
        case "slip":   return new SlipKnot();
        case "granny": return new GrannyKnot();
        case "bowline" return new BowlineKnot();

        default: throw new IllegalArgumentException();
    }
}

与查找相反：

static final Map<String, Supplier<KnotStrategy>> KNOTS = (
    new HashMap<String, Supplier<KnotStrategy>>()
);
static {
    KNOTS.put("slip", SlipKnot::new);
    KNOTS.put("granny", GrannyKnot::new);
    KNOTS.put("bowline", BowlineKnot::new);
}

static KnotStrategy getKnotStrategy(String name) {
    Supplier<KnotStrategy> supp = KNOTS.get(name);
    if(supp != null) {
        return supp.get();
    }

    throw new IllegalArgumentException();
}

但这不是策略模式的一部分。

But it's not part of the strategy pattern.

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