无法在原语类型double上调用compareTo（double） [英] Cannot invoke compareTo(double) on the primitive type double

问题描述

return array [index1] .compareTo（array [index2]）; 提供一个错误无法对原始类型调用compareTo 。如何解决这个问题？

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?

/*:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
/*::  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);

推荐答案

替换实例方法的调用 compareTo 与调用 static 比较方法，如下所示：

Replace the call of an instance method compareTo with the call of static compare method, like this:

return Double.compare(array[index1], array[index2]);

这样就可以保留 double 一个基本数组，并且在调用实例方法之前避免自动装箱。

This lets you keep your doubles in an array of primitives, and avoid autoboxing before calling an instance method.

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