这是我的 java 课程介绍的基本货币转换器。我应该能够使用静态汇率在日元、美元、英镑和欧元之间进行转换。它有效，但我很想知道我是否以最有效的方式做到了这一点。它看起来很长，看起来像一团糟。只是想要一些反馈。
import java.util.Scanner;
public class currency
{
public currency()
{
char us_dollar_sym = 36;
char pound_sym = 163;
char yen_sym = 165;
char euro_sym = 8364;
String us_dollar = "Dollars";
String pound = "Pounds";
String yen = "Yen";
String euro = "Euros";
double rate = 0;
// Interface
System.out.println("Welcome to the Currency Converter Program \n");
System.out.println("Use the following codes to input your currency choices: \n 1 - US dollars \n 2 - Euros \n 3 - British Pounds \n 4 - Japanese Yen \n");
//
System.out.println("Please choose the input currency:");
Scanner in = new Scanner(System.in);
int choice = in.nextInt();
String inType = null;
switch(choice) {
case 1: inType = "US Dollars >> " + us_dollar_sym; break;
case 2: inType = "Euros >> " + euro_sym; break;
case 3: inType = "British Pounds >> " + pound_sym; break;
case 4: inType = "Japanese Yen >> " + yen_sym; break;
default:
System.out.println("Please restart the program & enter a number from the list.");
return;
}
System.out.println("Please choose the output currency");
int output = in.nextInt();
System.out.printf("Now enter the input in " + inType);
double input = in.nextDouble();
if (choice == output)
System.out.println("Same currency no need to convert");
if (choice == 1 && output == 2)
{
double dollar_euro_rate = 0.78391;
rate = input * dollar_euro_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + dollar_euro_rate + " Dollars to %s = %.2f\n", (char)us_dollar_sym, euro, rate);
}
else if (choice == 1 && output == 3){
double dollar_pound_rate = 0.621484;
rate = input * dollar_pound_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + dollar_pound_rate + " Dollars to %s = %.2f\n", (char)us_dollar_sym, pound, rate);
}
else if (choice == 1 && output == 4){
double dollar_yen_rate = 107.174;
rate = input * dollar_yen_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + dollar_yen_rate + " Dollars to %s = %.2f\n", (char)us_dollar_sym, yen, rate);
}
if (choice == 2 && output == 1)
{
double euro_dollar_rate = 1.27579;
rate = input * euro_dollar_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + euro_dollar_rate + " Euros to %s = %.2f\n", (char)euro_sym, us_dollar, rate);
}
else if (choice == 2 && output == 3)
{
double euro_pound_rate = 0.792648;
rate = input * euro_pound_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + euro_pound_rate + " Euros to %s = %.2f\n", (char)euro_sym, pound, rate);
}
else if (choice == 2 && output == 4)
{
double euro_yen_rate = 136.708;
rate = input * euro_yen_rate;
System.out.printf( "%s" + input + " at a conversion rate of " + euro_yen_rate + " Euros to %s = %.2f\n", (char)euro_sym, yen, rate);
}
if (choice == 3 && output == 1)
{
double pound_dollar_rate = 1.60972;
System.out.printf( "%s" + input + " at a conversion rate of " + pound_dollar_rate + " Pounds to %s = %.2f\n", (char)pound_sym, us_dollar, rate);
}
else if (choice == 3 && output == 2)
{
double pound_euro_rate = 1.26161;
System.out.printf( "%s" + input + " at a conversion rate of " + pound_euro_rate + " Pounds to %s = %.2f\n", (char)pound_sym, euro, rate);
}
else if (choice == 3 && output == 4)
{
double pound_yen_rate = 172.511;
System.out.printf( "%s" + input + " at a conversion rate of " + pound_yen_rate + " Pounds to %s = %.2f\n", (char)pound_sym, yen, rate);
}
if (choice == 4 && output == 1)
{
double yen_dollar_rate = 0.00932574;
System.out.printf( "%s" + input + " at a conversion rate of " + yen_dollar_rate + " Yen to %s = %.2f\n", (char)yen_sym, us_dollar, rate);
}
else if (choice == 4 && output == 2)
{
double yen_euro_rate = 0.00730615;
System.out.printf( "%s" + input + " at a conversion rate of " + yen_euro_rate + " Yen to %s = %.2f\n", (char)yen_sym, euro, rate);
}
else if (choice == 4 && output == 3)
{
double yen_pound_rate = 0.00579135;
System.out.printf( "%s" + input + " at a conversion rate of " + yen_pound_rate + " Yen to %s = %.2f\n", (char)yen_sym, pound, rate);
}
System.out.println("Thank you for using the currency converter");
}
}
我一直对使用整数输入持谨慎态度。如果有人键入一个字符，您的程序可能会崩溃，因为会发生异常。接受数字字符可能是更安全的选择。
当您在同一 if 语句中检查“选择”和“输出”时，它需要更多资源。嵌套 if 语句可能会提高效率。这将有 if 语句可供选择，其中 if 语句用于输出。
由于您将货币称为 int，我将使用 n × m 矩阵来存储汇率。 n 将是第一种货币，m 是第二种货币。使用这两个 int，您可以追溯正确的汇率。
矩阵中的对角线为 1（因为 USD >> USD =1 ）。
最后，写一个函数来计算汇率并返回相应的文本（你可以使用一个hashmap，以int作为键，名称（string）作为值）
exchange_rate = currency[1][2];
HashMap hm = new HashMap();
hm.put(1, new string("USD");
等...
将所有费率表示为一个标准值的乘数，例如使用美元作为标准值。那么英镑的转换值为 1.60，美元为 1.0，欧元为 1.29。那么转换计算将是：
从价值 * 从转化 * 1/到转化
例如从 1 英镑到欧元将是：
1 * 1.60 * (1/1.29) = 1.24
如果您将所有费率存储在 HashMap 中，那么您可以完全避免 switch 语句。
为什么要使用这种方式来转换货币。你有JSR 354 Money and Currency API这里有一些你可以使用的例子，它真的很容易使用和快速：
MonetaryAmount monetaryAmount = Money.of(100.20, usd);
CurrencyUnit currency = monetaryAmount.getCurrency();
NumberValue numberValue = monetaryAmount.getNumber();
int value= numberValue.intValue();