Java : How to sort an array of floats in reverse order ?

Question

I use the following lines to sort an array of floats in reverse order, but I got an error message, what's wrong ?

float sortedData[]=new float[100];
  ...
Arrays.sort(sortedData,Collections.reverseOrder());

Error : cannot find symbol

symbol : method sort(float[],java.util.Comparator) location: class java.util.Arrays Arrays.sort(sortedData,Collections.reverseOrder());

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I was confused because in Jdk1.6 api, I saw this : [ Arrays ] public static void sort(float[] a), it doesn't say : public static void sort(Float[] a)

Answer 1

The compiler isn't lying to you. There isn't a method in Arrays called "sort" that takes an array of float and a Comparator. There is, however, a method called "sort" which takes an array of Objects and a Comparator. Perhaps if you converted your array to an array of Float before you called sort?

Think of it as a defect in Java's autoboxing if you will, that it can't autobox an array of primitives into an array of the equivalent Objects.

Answer 2

there is no Arrays.sort(float[], Comparator) method; however you can use or Arrays.asList() or just use a boxed Float[] array:

Float[] sortedData = new Float[100];
...
Arrays.sort(sortedData, Collections.reverseOrder());

In order to box a primitive array you can use the following code:

public static Float[] floatArray(float... components) {
    return toBoxedArray(Float.class, components);
}

private static <T> T[] toBoxedArray(Class<T> boxClass, Object components) {
    final int length = Array.getLength(components);
    Object res = Array.newInstance(boxClass, length);

    for (int i = 0; i < length; i++) {
        Array.set(res, i, Array.get(components, i));
    }

    return (T[]) res;
}

or include something like commons lang in your project and use ArrayUtils

Answer 3

That specific method, takes an array of type Object. The type float does not extend the Object class, but Float does.

Float sortedData[]=new Float[100];
...
Arrays.sort(sortedData,Collections.reverseOrder());

Answer 4

I suggest using a Arrays.sort(float[]) and then writing a method reverse(float[]) (you may or may not want to shift the NaNs around).

Answer 5

Others have explained why. Can you sort it first and then reverse it?