Java 无法对基本类型 double 调用 compareTo(double)
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Cannot invoke compareTo(double) on the primitive type double
提问by Klausos Klausos
The line return array[index1].compareTo(array[index2]);provides an error "Cannot invoke compareTo(double) on the primitive type double". How to solve this issue?
该行return array[index1].compareTo(array[index2]);提供了一个错误“无法在原始类型 double 上调用 compareTo(double)”。如何解决这个问题？
/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
/*:: This function implements a comparator of double values :*/
/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
private class ArrayIndexComparator implements Comparator<Integer>
{
private final double[] array;
public ArrayIndexComparator(double[] array)
{
this.array = array;
}
public Integer[] createIndexArray()
{
Integer[] indexes = new Integer[array.length];
for (int i = 0; i < array.length; i++)
{
indexes[i] = i; // Autoboxing
}
return indexes;
}
@Override
public int compare(Integer index1, Integer index2)
{
// Autounbox from Integer to int to use as array indexes
return array[index1].compareTo(array[index2]);
}
}
double[] dist = new double[centroids.size()];
// fill array...
ArrayIndexComparator comparator = new ArrayIndexComparator(dist);
Integer[] indexes = comparator.createIndexArray();
Arrays.sort(indexes, comparator);
采纳答案by dasblinkenlight
Replace the call of an instance method compareTowith the call of static comparemethod, like this:
将实例方法compareTo的调用替换为静态compare方法的调用，如下所示：
return Double.compare(array[index1], array[index2]);
This lets you keep your doubles in an array of primitives, and avoid autoboxing before calling an instance method.
这使您可以将doubles保存在原始数组中，并在调用实例方法之前避免自动装箱。
回答by Prabhakaran Ramaswamy
In java primitive types don't have any methods. Instead using primitive data types use Wrapper classes.
在 Java 原始类型中没有任何方法。使用 Wrapper 类代替使用原始数据类型。
change
改变
return array[index1].compareTo(array[index2]);
to
到
return new Double(array[index1]).compareTo(array[index2]);
or
或者
try with Double[] array;instead of double[] array;
尝试 Double[] array;代替 double[] array;
回答by RamonBoza
for primitive types do not use compareTo, use ==instead
对于原始类型不要使用compareTo，==而是使用
but if you want to use compareTojust create a Double array
但如果你想使用compareTo只是创建一个 Double 数组
Double[] dist = new Double[centroids.size()];
回答by nimish parikh
Primitive Types cannot be compared directly by a comparator, as the interface is only implemented by collator and RuleBasedCollator. No wrapper class implements comparator. Due to which compiler won't be able to auto box it.
原始类型不能由比较器直接比较，因为接口仅由 collator 和 RuleBasedCollator 实现。没有包装类实现比较器。由于哪个编译器将无法自动装箱。
Just look in Double class and you will find an inbuilt method which provides compare method.
只需查看 Double 类，您就会发现一个提供比较方法的内置方法。
public static int compare(double d1, double d2)
public static int compare(double d1, double d2)
Returns:the value 0 if d1 is numerically equal to d2; a value less than 0 if d1 is numerically less than d2; and a value greater than 0 if d1 is numerically greater than d2.
返回：如果 d1 在数字上等于 d2，则值为 0；如果 d1 在数值上小于 d2，则为小于 0 的值；如果 d1 在数值上大于 d2，则该值大于 0。
Reverse:Multiple the entire expression by -1;
反向：将整个表达式乘以-1；
