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

Question

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?

Answer 1

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");     } }