Name: gm110360 Date: 04/13/2004


A DESCRIPTION OF THE REQUEST :
Average performance gains of 5-10% for Arrays.sort(Object[]) and Collections.sort(List) are achievable by reducing the number of "Comparable"- typecasts used.
The proposed change maintains the original interface & semantics, and introduces only minimal code changes (cp. sample below with original implementation).

For a brief newsgroup discussion of this issue search for "Performance Improvement for Sorting", in comp.lang.java.programmer.


JUSTIFICATION :
this is a performance enhancement request / recommendation only, and as such "nice, but not strictly necessary"

SOURCE CODE:
---------- BEGIN SOURCE ----------
import java.util.List;
import java.util.ListIterator;

public final class SortWithComparables {

    public static void sort(List list) {
        Object[] a = null;
        try {
            a = list.toArray(new Comparable[0]);
        } catch (ArrayStoreException e) {
throw new ClassCastException();
        }
        sort(a);
        ListIterator i = list.listIterator();
        for (int j = 0, n = a.length; j < n; j++) {
            i.next(); i.set(a[j]);
        }
    }

    public static void sort(Object[] a) {
        mergeSort((Comparable[])a.clone(), (Comparable[])a, 0, a.length, 0);
    }

    private static void mergeSort(Comparable src[], Comparable dest[], int low, int high, int off) {
        // like original in Arrays.mergeSort(...), but without any Comparable[]-casts)
    }
}

---------- END SOURCE ----------
(Incident Review ID: 249779)
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