由于nextDouble()，我得到了一个异常，我怎样才能避免这种情况？
由于nextDouble()，我得到了一个异常，我怎样才能避免这种情况？
提问于 2015-11-06 12:38:07
我是美联社的计算机科学专家，我正在编写java代码。我可以使用的方法和类的数量是有限的。例如，我不被允许使用hasNextLine()。这是当我输入“多少欧元等于一美元”的值时，它给我的错误。它允许我输入该值，然后要求输入美元值。然而，在我输入它之前，这个错误就出现了：
Exception in thread "main" java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at CurrencyConverter.main(CurrencyConverter.java:20)public class Currency
{
private double rate;
public Currency()
{
rate = 0.0;
}
public Currency(double newRate)
{
rate = newRate;
}
public double convert(double dollar)
{
double euro = dollar * rate;
return euro;
}
}import java.util.Scanner;
import java.util.Scanner;
public class CurrencyConverter
{
public static void main(String [] args)
{
Scanner input = new Scanner(System.in);
System.out.println("How many euros is one dollar?");
double exchangerate = input.nextDouble();
System.out.println("Dollar value (Q to quit):");
String dollarvalue = input.nextLine();
double dv = 0.0;
String bvalue = "";
String bvaluetwo = "Q";
if (dollarvalue.equals(bvalue))
{
dollarvalue = "test";
}
else if (!dollarvalue.equals(bvaluetwo))
{
dv = Double.parseDouble(dollarvalue);
}
Currency exchange = new Currency(exchangerate);
while (dollarvalue != "Q")
{
double eurovalue = exchange.convert(dv);
System.out.println(dv + " dollar = " + eurovalue + " euro");
}
}
}回答 2
Stack Overflow用户
回答已采纳
发布于 2015-11-06 13:22:40
尝试将此代码放入您的main方法中：
public static void main(String [] args)
{
Scanner input = new Scanner(System.in);
System.out.println("How many euros is one dollar?");
double exchangerate = input.nextDouble();
//You have to put this in order to continue
input.nextLine();
System.out.println("Dollar value (Q to quit):");
String dollarvalue = input.nextLine();
double dv = 0.0;
String bvalue = "";
String bvaluetwo = "Q";
if (dollarvalue == bvalue)
{
dollarvalue = "test";
}
else if ((dollarvalue != bvaluetwo))
{
dv = Double.parseDouble(dollarvalue);
}
Currency exchange = new Currency(exchangerate);
while (!dollarvalue.equals("Q"))
{
double eurovalue = exchange.convert(dv);
System.out.println(dv + " dollar = " + eurovalue + " euro");
System.out.println("Dollar value (Q to quit):");
dollarvalue = input.nextLine();
if (!dollarvalue.equals("Q")) {
dv = Double.parseDouble(dollarvalue);
eurovalue = exchange.convert(dv);
System.out.println(dv + " dollar = " + eurovalue + " euro");
}
}
System.out.println("You pressed Q, have a nice day");
}
}Stack Overflow用户
发布于 2015-11-06 12:43:26
如果没有输入，这将给出异常，在调用任何next方法之前，请始终使用扫描器的hasNext()方法
这是你的罪魁祸首：
System.out.println("Dollar value (Q to quit):");
String dollarvalue = input.nextLine();
double dv = 0.0;
String bvalue = "";
String bvaluetwo = "Q";
if (dollarvalue == bvalue) {
dollarvalue = "test";
} else if ((dollarvalue != bvaluetwo)) {
dv = Double.parseDouble(dollarvalue);
}您存储的是"Q“的String或用户输入的其他字符串值，然后在dv = Double.parseDouble(dollarvalue);中，您正在将其解析(转换)为抛出java.lang.NumberFormatException异常的double
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/33559589
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