如何使用许多if语句提高方法的可读性和长度？ [英] How can I improve readability and length of a method with many if statements?

问题描述

我有195个ifs的方法。这是一个简短的版本：

I have a method with 195 ifs. Here is a shorter version:

private BigDecimal calculateTax(String country, BigDecimal amount) throws Exception {
    if(country.equals("POLAND")){
        return new BigDecimal(0.23).multiply(amount);
    }
    else if(country.equals("AUSTRIA")) {
        return new BigDecimal(0.20).multiply(amount);
    }
    else if(country.equals("CYPRUS")) {
        return new BigDecimal(0.19).multiply(amount);
    }
    else {
        throw new Exception("Country not supported");
    }
}

我可以更改if开关：

private BigDecimal calculateTax(String country, BigDecimal amount) throws Exception {
    switch (country) {
        case "POLAND":
            return new BigDecimal(0.23).multiply(amount);
        case "AUSTRIA":
            return new BigDecimal(0.20).multiply(amount);
        case "CYPRUS":
            return new BigDecimal(0.19).multiply(amount);
        default:
            throw new Exception("Country not supported");
    }
}

，但是195个案例仍然很长。如何改善该方法的可读性和长度？在这种情况下哪种模式是最好的？

but 195 cases is still so long. How could I improve readability and length of that method? What pattern would be the best in this case?

推荐答案

创建 Map< String，Double> ，将国家/地区名称映射到相应的税率：

Create a Map<String,Double> that maps country names to their corresponding tax rates:

Map<String,Double> taxRates = new HashMap<> ();
taxRates.put("POLAND",0.23);
...

使用该地图如下：

private BigDecimal calculateTax(String country, BigDecimal amount) throws Exception {
    if (taxRates.containsKey(country)) {
        return new BigDecimal(taxRates.get(country)).multiply(amount);
    } else {
        throw new Exception("Country not supported");
    }
}

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