Java HashSet 到数组
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Java HashSet to array
提问by PenguinProgrammer
I'm trying to convert a HashSet to an Array of Doubles. Yes I have a main method and class defined, I've just included what I've imported as well as the code for this specific function.
我正在尝试将 HashSet 转换为双精度数组。是的，我定义了一个主要的方法和类，我刚刚包含了我导入的内容以及这个特定函数的代码。
This is the Error that shows up:
这是显示的错误：
Ass10.java:148: error: no suitable method found for toArray(double[])
rtrn = s.toArray(rtrn);
Here is the code:
这是代码：
import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Set;
import java.util.HashSet;
public static double[] negated(double[] a) {
Set<Double> s = new HashSet<Double>();
for(double x : a) {
s.add(x);
} for(double x : s) {
if(s.contains(-x) == false) {
s.remove(x);
}
}
double[] rtrn = new double[s.size()];
rtrn = s.toArray(rtrn);
return rtrn;
}
采纳答案by Costi Ciudatu
You can't use a primitive array in this scenario, as there's no auto-boxing for arrays in Java. Use a Double[]for that to work.
在这种情况下不能使用原始数组，因为 Java 中没有数组的自动装箱。使用 aDouble[]来工作。
回答by peter.petrov
This is a compile time error, right? Try using Double[] instead of double[].
这是一个编译时错误，对吧？尝试使用 Double[] 而不是 double[]。
回答by Sage
Java collections works with reference type. The function Collection.toArray(T[] a)has a signature of generic reference type. So you will need to pass a reference type array instead of primitive array. The corresponding reference type of primitive type doubleis Double.
Java 集合使用引用类型。该函数Collection.toArray(T[] a)具有通用引用类型的签名。所以你需要传递一个引用类型数组而不是原始数组。原始类型对应的引用类型double是Double.
Double[] rtrn = new Double[s.size()];
rtrn = s.toArray(rtrn);
