eclipse 从 ArrayList 转换为 double[] 时出错？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/14134527/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Error converting from ArrayList to double[]?
提问by Rahul
I have an ArrayListcalled out, and I need to convert it to a double[]. The examples I've found online have said two things:
我有一个ArrayList电话out，我需要将其转换为double[]. 我在网上找到的例子说了两件事：
First, try:
第一次尝试：
double[] d = new double[out.size()];
out.toArray(d);
However, this produces the error (eclipse):
但是，这会产生错误（eclipse）：
The method toArray(T[]) in the type List<Double> is not applicable for the arguments (double[]).
The second solution I found was on StackOverflow, and was:
我找到的第二个解决方案是在 StackOverflow 上，它是：
double[] dx = Arrays.copyOf(out.toArray(), out.toArray().length, double[].class);
However, this produces the error:
但是，这会产生错误：
The method copyOf(U[], int, Class<? extends T[]>) in the type Arrays is not applicable for the arguments (Object[], int, Class<double[]>)
What is causing these errors, and how do I convert outto double[]without creating these problems? outindeed holds only double values.
是什么导致了这些错误，以及如何out在double[]不产生这些问题的情况下转换为？out确实只有双重价值。
Thanks!
谢谢！
回答by Rahul
I think you are trying to convert ArrayListcontaining Doubleobjects to primitive double[]
我认为您正在尝试将ArrayList包含Double对象转换为原始对象double[]
public static double[] convertDoubles(List<Double> doubles)
{
double[] ret = new double[doubles.size()];
Iterator<Double> iterator = doubles.iterator();
int i = 0;
while(iterator.hasNext())
{
ret[i] = iterator.next();
i++;
}
return ret;
}
ALternately, Apache Commons has a ArrayUtilsclass, which has a method toPrimitive()
或者，Apache Commons 有一个ArrayUtils类，它有一个方法toPrimitive()
ArrayUtils.toPrimitive(out.toArray(new Double[out.size()]));
but i feel it is pretty easy to do this by yourself as shown above instead of using external libraries.
但我觉得自己做这件事很容易，如上所示，而不是使用外部库。
回答by Karthik T
Have you tried
你有没有尝试过
Double[] d = new Double[out.size()];
out.toArray(d);
i.e use the class Doubleand not the primitive type double
即使用类Double而不是原始类型double
The error messages seem to imply that this is the issue. After all, since Doubleis a wrapper class around the primitive type doubleit is essentially a different type, and compiler will treat it as such.
错误消息似乎暗示这是问题所在。毕竟，由于Double是原始类型的包装类，double它本质上是一种不同的类型，编译器会这样对待它。
回答by Avinash T.
Generics does not work with primitive types that's why you are getting an error. Use Double arrayinstead of primitive double. Try this -
泛型不适用于原始类型，这就是您收到错误的原因。使用Double array代替primitive double。尝试这个 -
Double[] d = new Double[out.size()];
out.toArray(d);
double[] d1 = ArrayUtils.toPrimitive(d);
