Class Arrays
public class Arrays
extends java.lang.Object
In addition to commodity methods, this class contains Swapper
based implementations
of quicksort and of
a stable, inplace mergesort. These
generic sorting methods can be used to sort any kind of list, but they find their natural
usage, for instance, in sorting arrays in parallel.
Some algorithms provide a parallel version that will by default use the
common pool, but this can be overridden by calling the
function in a task already in the ForkJoinPool
that the operation should run in. For example,
something along the lines of "poolToParallelSortIn.invoke(() > parallelQuickSort(arrayToSort))
"
will run the parallel sort in poolToParallelSortIn
instead of the default pool.
 See Also:
Arrays

Field Summary
Fields Modifier and Type Field Description static int
MAX_ARRAY_SIZE
This is a safe value used byArrayList
(as of Java 7) to avoid throwingOutOfMemoryError
on some JVMs. 
Method Summary
Modifier and Type Method Description static void
ensureFromTo(int arrayLength, int from, int to)
Ensures that a range given by its first (inclusive) and last (exclusive) elements fits an array of given length.static void
ensureOffsetLength(int arrayLength, int offset, int length)
Ensures that a range given by an offset and a length fits an array of given length.static void
mergeSort(int from, int to, IntComparator c, Swapper swapper)
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using mergesort.static void
parallelQuickSort(int from, int to, IntComparator comp, Swapper swapper)
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using a parallel quicksort.static void
quickSort(int from, int to, IntComparator comp, Swapper swapper)
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using parallel quicksort.Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

MAX_ARRAY_SIZE
public static final int MAX_ARRAY_SIZEThis is a safe value used byArrayList
(as of Java 7) to avoid throwingOutOfMemoryError
on some JVMs. We adopt the same value. See Also:
 Constant Field Values


Method Details

ensureFromTo
public static void ensureFromTo(int arrayLength, int from, int to)Ensures that a range given by its first (inclusive) and last (exclusive) elements fits an array of given length.This method may be used whenever an array range check is needed.
In Java 9 and up, this method should be considered deprecated in favor of the
Objects.checkFromToIndex(int, int, int)
method, which may be intrinsified in recent JVMs. Parameters:
arrayLength
 an array length.from
 a start index (inclusive).to
 an end index (inclusive). Throws:
java.lang.IllegalArgumentException
 iffrom
is greater thanto
.java.lang.ArrayIndexOutOfBoundsException
 iffrom
orto
are greater thanarrayLength
or negative.

ensureOffsetLength
public static void ensureOffsetLength(int arrayLength, int offset, int length)Ensures that a range given by an offset and a length fits an array of given length.This method may be used whenever an array range check is needed.
In Java 9 and up, this method should be considered deprecated in favor of the
Objects.checkFromIndexSize(int, int, int)
method, which may be intrinsified in recent JVMs. Parameters:
arrayLength
 an array length.offset
 a start index for the fragmentlength
 a length (the number of elements in the fragment). Throws:
java.lang.IllegalArgumentException
 iflength
is negative.java.lang.ArrayIndexOutOfBoundsException
 ifoffset
is negative oroffset
+length
is greater thanarrayLength
.

mergeSort
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using mergesort.This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort. The sorting algorithm is an inplace mergesort that is significantly slower than a standard mergesort, as its running time is O(n (log n)^{2}), but it does not allocate additional memory; as a result, it can be used as a generic sorting algorithm.
 Parameters:
from
 the index of the first element (inclusive) to be sorted.to
 the index of the last element (exclusive) to be sorted.c
 the comparator to determine the order of the generic data (arguments are positions).swapper
 an object that knows how to swap the elements at any two positions.

parallelQuickSort
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using a parallel quicksort.The sorting algorithm is a tuned quicksort adapted from Jon L. Bentley and M. Douglas McIlroy, “Engineering a Sort Function”, Software: Practice and Experience, 23(11), pages 1249−1265, 1993.
 Parameters:
from
 the index of the first element (inclusive) to be sorted.to
 the index of the last element (exclusive) to be sorted.comp
 the comparator to determine the order of the generic data.swapper
 an object that knows how to swap the elements at any two positions.

quickSort
Sorts the specified range of elements using the specified swapper and according to the order induced by the specified comparator using parallel quicksort.The sorting algorithm is a tuned quicksort adapted from Jon L. Bentley and M. Douglas McIlroy, “Engineering a Sort Function”, Software: Practice and Experience, 23(11), pages 1249−1265, 1993.
 Parameters:
from
 the index of the first element (inclusive) to be sorted.to
 the index of the last element (exclusive) to be sorted.comp
 the comparator to determine the order of the generic data.swapper
 an object that knows how to swap the elements at any two positions.
