How can I improve readability and length of a method with many if statements?

Michu93 :

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");
    }
}

I can change ifs to switches:

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");
    }
}

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?

Eran :

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);
...

Use that Map as follows:

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");
    }
}