/*
* @(#)Arrays.java 1.59 04/04/01
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package tests.java15.util;
import tests.java15.lang.Math;
/**
* This class contains various methods for manipulating arrays (such as
* sorting and searching). This class also contains a static factory
* that allows arrays to be viewed as lists.
*
* <p>The methods in this class all throw a <tt>NullPointerException</tt> if
* the specified array reference is null, except where noted.
*
* <p>The documentation for the methods contained in this class includes
* briefs description of the <i>implementations</i>. Such descriptions should
* be regarded as <i>implementation notes</i>, rather than parts of the
* <i>specification</i>. Implementors should feel free to substitute other
* algorithms, so long as the specification itself is adhered to. (For
* example, the algorithm used by <tt>sort(Object[])</tt> does not have to be
* a mergesort, but it does have to be <i>stable</i>.)
*
* <p>This class is a member of the
* <a href="{@docRoot}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @author Neal Gafter
* @version 1.59, 04/01/04
* @see Comparable
* @see Comparator
* @since 1.2
*/
public class Arrays {
// Suppresses default constructor, ensuring non-instantiability.
private Arrays() {
}
// Sorting
/**
* Sorts the specified array of ints into ascending numerical order.
* The sorting algorithm is a tuned quicksort, adapted from Jon
* L. Bentley and M. Douglas McIlroy's "Engineering a Sort Function",
* Software-Practice and Experience, Vol. 23(11) P. 1249-1265 (November
* 1993). This algorithm offers n*log(n) performance on many data sets
* that cause other quicksorts to degrade to quadratic performance.
*
* @param a the array to be sorted.
*/
public static void sort(int[] a) {
sort1(a, 0, a.length);
}
/**
* Sorts the specified sub-array of integers into ascending order.
*/
private static void sort1(int x[], int off, int len) {
// Insertion sort on smallest arrays
if (len < 7) {
for (int i=off; i<len+off; i++)
for (int j=i; j>off && x[j-1]>x[j]; j--)
swap(x, j, j-1);
return;
}
// Choose a partition element, v
int m = off + (len >> 1); // Small arrays, middle element
if (len > 7) {
int l = off;
int n = off + len - 1;
/*
if (len > 40) { // Big arrays, pseudomedian of 9
int s = len/8;
l = med3(x, l, l+s, l+2*s);
m = med3(x, m-s, m, m+s);
n = med3(x, n-2*s, n-s, n);
}
*/
m = med3(x, l, m, n); // Mid-size, med of 3
}
int v = x[m];
// Establish Invariant: v* (<v)* (>v)* v*
int a = off, b = a, c = off + len - 1, d = c;
while(true) {
while (b <= c && x[b] <= v) {
if (x[b] == v)
swap(x, a++, b);
b++;
}
while (c >= b && x[c] >= v) {
if (x[c] == v)
swap(x, c, d--);
c--;
}
if (b > c)
break;
swap(x, b++, c--);
}
// Swap partition elements back to middle
int s, n = off + len;
s = Math.min(a-off, b-a ); vecswap(x, off, b-s, s);
s = Math.min(d-c, n-d-1); vecswap(x, b, n-s, s);
// Recursively sort non-partition-elements
if ((s = b-a) > 1)
sort1(x, off, s);
if ((s = d-c) > 1)
sort1(x, n-s, s);
}
/**
* Swaps x[a] with x[b].
*/
private static void swap(int x[], int a, int b) {
int t = x[a];
x[a] = x[b];
x[b] = t;
}
/**
* Swaps x[a .. (a+n-1)] with x[b .. (b+n-1)].
*/
private static void vecswap(int x[], int a, int b, int n) {
for (int i=0; i<n; i++, a++, b++)
swap(x, a, b);
}
/**
* Returns the index of the median of the three indexed integers.
*/
private static int med3(int x[], int a, int b, int c) {
return (x[a] < x[b] ?
(x[b] < x[c] ? b : x[a] < x[c] ? c : a) :
(x[b] > x[c] ? b : x[a] > x[c] ? c : a));
}
/**
* Sorts the specified array of objects into ascending order, according to
* the <i>natural ordering</i> of its elements. All elements in the array
* must implement the <tt>Comparable</tt> interface. Furthermore, all
* elements in the array must be <i>mutually comparable</i> (that is,
* <tt>e1.compareTo(e2)</tt> must not throw a <tt>ClassCastException</tt>
* for any elements <tt>e1</tt> and <tt>e2</tt> in the array).<p>
*
* This sort is guaranteed to be <i>stable</i>: equal elements will
* not be reordered as a result of the sort.<p>
*
* The sorting algorithm is a modified mergesort (in which the merge is
* omitted if the highest element in the low sublist is less than the
* lowest element in the high sublist). This algorithm offers guaranteed
* n*log(n) performance.
*
* @param a the array to be sorted.
* @throws ClassCastException if the array contains elements that are not
* <i>mutually comparable</i> (for example, strings and integers).
* @see Comparable
*/
public static void sort(Object[] a) {
Object[] aux = (Object[])a.clone();
mergeSort(aux, a, 0, a.length, 0);
}
/**
* Tuning parameter: list size at or below which insertion sort will be
* used in preference to mergesort or quicksort.
*/
private static final int INSERTIONSORT_THRESHOLD = 7;
/**
* Src is the source array that starts at index 0
* Dest is the (possibly larger) array destination with a possible offset
* low is the index in dest to start sorting
* high is the end index in dest to end sorting
* off is the offset to generate corresponding low, high in src
*/
private static void mergeSort(Object[] src,
Object[] dest,
int low,
int high,
int off) {
int length = high - low;
// Insertion sort on smallest arrays
if (length < INSERTIONSORT_THRESHOLD) {
for (int i=low; i<high; i++)
for (int j=i; j>low &&
((Comparable) dest[j-1]).compareTo(dest[j])>0; j--)
swap(dest, j, j-1);
return;
}
// Recursively sort halves of dest into src
int destLow = low;
int destHigh = high;
low += off;
high += off;
int mid = (low + high) >> 1;
mergeSort(dest, src, low, mid, -off);
mergeSort(dest, src, mid, high, -off);
// If list is already sorted, just copy from src to dest. This is an
// optimization that results in faster sorts for nearly ordered lists.
if (((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {
System.arraycopy(src, low, dest, destLow, length);
return;
}
// Merge sorted halves (now in src) into dest
for(int i = destLow, p = low, q = mid; i < destHigh; i++) {
if (q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)
dest[i] = src[p++];
else
dest[i] = src[q++];
}
}
/**
* Swaps x[a] with x[b].
*/
private static void swap(Object[] x, int a, int b) {
Object t = x[a];
x[a] = x[b];
x[b] = t;
}
}