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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

*

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* under the terms of the GNU General Public License version 2 only, as

* published by the Free Software Foundation. Oracle designates this

* particular file as subject to the "Classpath" exception as provided

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*

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* accompanied this code).

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*

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package java.util;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.io.Serializable;

import java.lang.reflect.Array;

import java.util.function.BiConsumer;

import java.util.function.BiFunction;

import java.util.function.Consumer;

import java.util.function.Function;

import java.util.function.IntFunction;

import java.util.function.Predicate;

import java.util.function.UnaryOperator;

import java.util.random.RandomGenerator;

import java.util.stream.IntStream;

import java.util.stream.Stream;

import java.util.stream.StreamSupport;

import jdk.internal.access.SharedSecrets;

import jdk.internal.vm.annotation.AOTSafeClassInitializer;

/**

* This class consists exclusively of static methods that operate on or return

* collections. It contains polymorphic algorithms that operate on

* collections, "wrappers", which return a new collection backed by a

* specified collection, and a few other odds and ends.

*

* <p>The methods of this class all throw a {@code NullPointerException}

* if the collections or class objects provided to them are null.

*

* <p>The documentation for the polymorphic algorithms contained in this class

* generally includes a brief description of the <i>implementation</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 {@code sort} does not have to be

* a mergesort, but it does have to be <i>stable</i>.)

*

* <p>The "destructive" algorithms contained in this class, that is, the

* algorithms that modify the collection on which they operate, are specified

* to throw {@code UnsupportedOperationException} if the collection does not

* support the appropriate mutation primitive(s), such as the {@code set}

* method. These algorithms may, but are not required to, throw this

* exception if an invocation would have no effect on the collection. For

* example, invoking the {@code sort} method on an unmodifiable list that is

* already sorted may or may not throw {@code UnsupportedOperationException}.

*

* <p>This class is a member of the

* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">

* Java Collections Framework</a>.

*

* @author Josh Bloch

* @author Neal Gafter

* @see Collection

* @see Set

* @see List

* @see Map

* @since 1.2

*/

@AOTSafeClassInitializer

public final class Collections {

// Suppresses default constructor, ensuring non-instantiability.

private Collections() {

}

// Algorithms

/*

* Tuning parameters for algorithms - Many of the List algorithms have

* two implementations, one of which is appropriate for RandomAccess

* lists, the other for "sequential." Often, the random access variant

* yields better performance on small sequential access lists. The

* tuning parameters below determine the cutoff point for what constitutes

* a "small" sequential access list for each algorithm. The values below

* were empirically determined to work well for LinkedList. Hopefully

* they should be reasonable for other sequential access List

* implementations. Those doing performance work on this code would

* do well to validate the values of these parameters from time to time.

* (The first word of each tuning parameter name is the algorithm to which

* it applies.)

*/

private static final int BINARYSEARCH_THRESHOLD = 5000;

private static final int REVERSE_THRESHOLD = 18;

private static final int SHUFFLE_THRESHOLD = 5;

private static final int FILL_THRESHOLD = 25;

private static final int ROTATE_THRESHOLD = 100;

private static final int COPY_THRESHOLD = 10;

private static final int REPLACEALL_THRESHOLD = 11;

private static final int INDEXOFSUBLIST_THRESHOLD = 35;

/**

* Sorts the specified list into ascending order, according to the

* {@linkplain Comparable natural ordering} of its elements.

* All elements in the list must implement the {@link Comparable}

* interface. Furthermore, all elements in the list must be

* <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}

* must not throw a {@code ClassCastException} for any elements

* {@code e1} and {@code e2} in the list).

*

* <p>This sort is guaranteed to be <i>stable</i>: equal elements will

* not be reordered as a result of the sort.

*

* <p>The specified list must be modifiable, but need not be resizable.

*

* @implNote

* This implementation defers to the {@link List#sort(Comparator)}

* method using the specified list and a {@code null} comparator.

*

* @param <T> the class of the objects in the list

* @param list the list to be sorted.

* @throws ClassCastException if the list contains elements that are not

* <i>mutually comparable</i> (for example, strings and integers).

* @throws UnsupportedOperationException if the specified list's

* list-iterator does not support the {@code set} operation.

* @throws IllegalArgumentException (optional) if the implementation

* detects that the natural ordering of the list elements is

* found to violate the {@link Comparable} contract

* @see List#sort(Comparator)

*/

public static <T extends Comparable<? super T>> void sort(List<T> list) {

list.sort(null);

}

/**

* Sorts the specified list according to the order induced by the

* specified comparator. All elements in the list must be <i>mutually

* comparable</i> using the specified comparator (that is,

* {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}

* for any elements {@code e1} and {@code e2} in the list).

*

* <p>This sort is guaranteed to be <i>stable</i>: equal elements will

* not be reordered as a result of the sort.

*

* <p>The specified list must be modifiable, but need not be resizable.

*

* @implNote

* This implementation defers to the {@link List#sort(Comparator)}

* method using the specified list and comparator.

*

* @param <T> the class of the objects in the list

* @param list the list to be sorted.

* @param c the comparator to determine the order of the list. A

* {@code null} value indicates that the elements' <i>natural

* ordering</i> should be used.

* @throws ClassCastException if the list contains elements that are not

* <i>mutually comparable</i> using the specified comparator.

* @throws UnsupportedOperationException if the specified list's

* list-iterator does not support the {@code set} operation.

* @throws IllegalArgumentException (optional) if the comparator is

* found to violate the {@link Comparator} contract

* @see List#sort(Comparator)

*/

public static <T> void sort(List<T> list, Comparator<? super T> c) {

list.sort(c);

}

/**

* Searches the specified list for the specified object using the binary

* search algorithm. The list must be sorted into ascending order

* according to the {@linkplain Comparable natural ordering} of its

* elements (as by the {@link #sort(List)} method) prior to making this

* call. If it is not sorted, the results are undefined. If the list

* contains multiple elements equal to the specified object, there is no

* guarantee which one will be found.

*

* <p>This method runs in log(n) time for a "random access" list (which

* provides near-constant-time positional access). If the specified list

* does not implement the {@link RandomAccess} interface and is large,

* this method will do an iterator-based binary search that performs

* O(n) link traversals and O(log n) element comparisons.

*

* @param <T> the class of the objects in the list

* @param list the list to be searched.

* @param key the key to be searched for.

* @return the index of the search key, if it is contained in the list;

* otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The

* <i>insertion point</i> is defined as the point at which the

* key would be inserted into the list: the index of the first

* element greater than the key, or {@code list.size()} if all

* elements in the list are less than the specified key. Note

* that this guarantees that the return value will be &gt;= 0 if

* and only if the key is found.

* @throws ClassCastException if the list contains elements that are not

* <i>mutually comparable</i> (for example, strings and

* integers), or the search key is not mutually comparable

* with the elements of the list.

*/

public static <T>

int binarySearch(List<? extends Comparable<? super T>> list, T key) {

if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)

return Collections.indexedBinarySearch(list, key);

else

return Collections.iteratorBinarySearch(list, key);

}

private static <T>

int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) {

int low = 0;

int high = list.size()-1;

while (low <= high) {

int mid = (low + high) >>> 1;

Comparable<? super T> midVal = list.get(mid);

int cmp = midVal.compareTo(key);

if (cmp < 0)

low = mid + 1;

else if (cmp > 0)

high = mid - 1;

else

return mid; // key found

}

return -(low + 1); // key not found

}

private static <T>

int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)

{

int low = 0;

int high = list.size()-1;

ListIterator<? extends Comparable<? super T>> i = list.listIterator();

while (low <= high) {

int mid = (low + high) >>> 1;

Comparable<? super T> midVal = get(i, mid);

int cmp = midVal.compareTo(key);

if (cmp < 0)

low = mid + 1;

else if (cmp > 0)

high = mid - 1;

else

return mid; // key found

}

return -(low + 1); // key not found

}

/**

* Gets the ith element from the given list by repositioning the specified

* list listIterator.

*/

private static <T> T get(ListIterator<? extends T> i, int index) {

T obj;

int pos = i.nextIndex();

if (pos <= index) {

do {

obj = i.next();

} while (pos++ < index);

} else {

do {

obj = i.previous();

} while (--pos > index);

}

return obj;

}

/**

* Searches the specified list for the specified object using the binary

* search algorithm. The list must be sorted into ascending order

* according to the specified comparator (as by the

* {@link #sort(List, Comparator) sort(List, Comparator)}

* method), prior to making this call. If it is

* not sorted, the results are undefined. If the list contains multiple

* elements equal to the specified object, there is no guarantee which one

* will be found.

*

* <p>This method runs in log(n) time for a "random access" list (which

* provides near-constant-time positional access). If the specified list

* does not implement the {@link RandomAccess} interface and is large,

* this method will do an iterator-based binary search that performs

* O(n) link traversals and O(log n) element comparisons.

*

* @param <T> the class of the objects in the list

* @param list the list to be searched.

* @param key the key to be searched for.

* @param c the comparator by which the list is ordered.

* A {@code null} value indicates that the elements'

* {@linkplain Comparable natural ordering} should be used.

* @return the index of the search key, if it is contained in the list;

* otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The

* <i>insertion point</i> is defined as the point at which the

* key would be inserted into the list: the index of the first

* element greater than the key, or {@code list.size()} if all

* elements in the list are less than the specified key. Note

* that this guarantees that the return value will be &gt;= 0 if

* and only if the key is found.

* @throws ClassCastException if the list contains elements that are not

* <i>mutually comparable</i> using the specified comparator,

* or the search key is not mutually comparable with the

* elements of the list using this comparator.

*/

@SuppressWarnings("unchecked")

public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {

if (c==null)

return binarySearch((List<? extends Comparable<? super T>>) list, key);

if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)

return Collections.indexedBinarySearch(list, key, c);

else

return Collections.iteratorBinarySearch(list, key, c);

}

private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {

int low = 0;

int high = l.size()-1;

while (low <= high) {

int mid = (low + high) >>> 1;

T midVal = l.get(mid);

int cmp = c.compare(midVal, key);

if (cmp < 0)

low = mid + 1;

else if (cmp > 0)

high = mid - 1;

else

return mid; // key found

}

return -(low + 1); // key not found

}

private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {

int low = 0;

int high = l.size()-1;

ListIterator<? extends T> i = l.listIterator();

while (low <= high) {

int mid = (low + high) >>> 1;

T midVal = get(i, mid);

int cmp = c.compare(midVal, key);

if (cmp < 0)

low = mid + 1;

else if (cmp > 0)

high = mid - 1;

else

return mid; // key found

}

return -(low + 1); // key not found

}

/**

* Reverses the order of the elements in the specified list.<p>

*

* This method runs in linear time.

*

* @apiNote

* This method mutates the specified list in-place. To obtain a

* reverse-ordered view of a list without mutating it, use the

* {@link List#reversed List.reversed} method.

*

* @param list the list whose elements are to be reversed.

* @throws UnsupportedOperationException if the specified list or

* its list-iterator does not support the {@code set} operation.

* @see List#reversed List.reversed

*/

@SuppressWarnings({"rawtypes", "unchecked"})

public static void reverse(List<?> list) {

int size = list.size();

if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {

for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)

swap(list, i, j);

} else {

// instead of using a raw type here, it's possible to capture

// the wildcard but it will require a call to a supplementary

// private method

ListIterator fwd = list.listIterator();

ListIterator rev = list.listIterator(size);

for (int i=0, mid=list.size()>>1; i<mid; i++) {

Object tmp = fwd.next();

fwd.set(rev.previous());

rev.set(tmp);

}

}

}

/**

* Randomly permutes the specified list using a default source of

* randomness. All permutations occur with approximately equal

* likelihood.

*

* <p>The hedge "approximately" is used in the foregoing description because

* default source of randomness is only approximately an unbiased source

* of independently chosen bits. If it were a perfect source of randomly

* chosen bits, then the algorithm would choose permutations with perfect

* uniformity.

*

* <p>This implementation traverses the list backwards, from the last

* element up to the second, repeatedly swapping a randomly selected element

* into the "current position". Elements are randomly selected from the

* portion of the list that runs from the first element to the current

* position, inclusive.

*

* @implSpec This method runs in linear time. If the specified list does

* not implement the {@link RandomAccess} interface and is large, this

* implementation dumps the specified list into an array before shuffling

* it, and dumps the shuffled array back into the list. This avoids the

* quadratic behavior that would result from shuffling a "sequential

* access" list in place.

*

* @param list the list to be shuffled.

* @throws UnsupportedOperationException if the specified list or

* its list-iterator does not support the {@code set} operation.

*/

public static void shuffle(List<?> list) {

Random rnd = r;

if (rnd == null)

r = rnd = new Random(); // harmless race.

shuffle(list, rnd);

}

private static Random r;

/**

* Randomly permute the specified list using the specified source of

* randomness.<p>

*

* This method is equivalent to {@link #shuffle(List, RandomGenerator)}

* and exists for backward compatibility. The {@link #shuffle(List, RandomGenerator)}

* method is preferred, as it is not limited to random generators

* that extend the {@link Random} class.

*

* @param list the list to be shuffled.

* @param rnd the source of randomness to use to shuffle the list.

* @throws UnsupportedOperationException if the specified list or its

* list-iterator does not support the {@code set} operation.

*/

public static void shuffle(List<?> list, Random rnd) {

shuffle(list, (RandomGenerator) rnd);

}

/**

* Randomly permute the specified list using the specified source of

* randomness. All permutations occur with equal likelihood

* assuming that the source of randomness is fair.<p>

*

* This implementation traverses the list backwards, from the last element

* up to the second, repeatedly swapping a randomly selected element into

* the "current position". Elements are randomly selected from the

* portion of the list that runs from the first element to the current

* position, inclusive.

*

* @implSpec This method runs in linear time. If the specified list does

* not implement the {@link RandomAccess} interface and is large, this

* implementation dumps the specified list into an array before shuffling

* it, and dumps the shuffled array back into the list. This avoids the

* quadratic behavior that would result from shuffling a "sequential

* access" list in place.

*

* @param list the list to be shuffled.

* @param rnd the source of randomness to use to shuffle the list.

* @throws UnsupportedOperationException if the specified list or its

* list-iterator does not support the {@code set} operation.

* @since 21

*/

@SuppressWarnings({"rawtypes", "unchecked"})

public static void shuffle(List<?> list, RandomGenerator rnd) {

int size = list.size();

if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {

for (int i=size; i>1; i--)

swap(list, i-1, rnd.nextInt(i));

} else {

Object[] arr = list.toArray();

// Shuffle array

for (int i=size; i>1; i--)

swap(arr, i-1, rnd.nextInt(i));

// Dump array back into list

// instead of using a raw type here, it's possible to capture

// the wildcard but it will require a call to a supplementary

// private method

ListIterator it = list.listIterator();

for (Object e : arr) {

it.next();

it.set(e);

}

}

}

/**

* Swaps the elements at the specified positions in the specified list.

* (If the specified positions are equal, invoking this method leaves

* the list unchanged.)

*

* @param list The list in which to swap elements.

* @param i the index of one element to be swapped.

* @param j the index of the other element to be swapped.

* @throws IndexOutOfBoundsException if either {@code i} or {@code j}

* is out of range (i &lt; 0 || i &gt;= list.size()

* || j &lt; 0 || j &gt;= list.size()).

* @since 1.4

*/

@SuppressWarnings({"rawtypes", "unchecked"})

public static void swap(List<?> list, int i, int j) {

// instead of using a raw type here, it's possible to capture

// the wildcard but it will require a call to a supplementary

// private method

final List l = list;

l.set(i, l.set(j, l.get(i)));

}

/**

* Swaps the two specified elements in the specified array.

*/

private static void swap(Object[] arr, int i, int j) {

Object tmp = arr[i];

arr[i] = arr[j];

arr[j] = tmp;

}

/**

* Replaces all of the elements of the specified list with the specified

* element. <p>

*

* This method runs in linear time.

*

* @param <T> the class of the objects in the list

* @param list the list to be filled with the specified element.

* @param obj The element with which to fill the specified list.

* @throws UnsupportedOperationException if the specified list or its

* list-iterator does not support the {@code set} operation.

*/

public static <T> void fill(List<? super T> list, T obj) {

int size = list.size();

if (size < FILL_THRESHOLD || list instanceof RandomAccess) {

for (int i=0; i<size; i++)

list.set(i, obj);

} else {

ListIterator<? super T> itr = list.listIterator();

for (int i=0; i<size; i++) {

itr.next();

itr.set(obj);

}

}

}

/**

* Copies all of the elements from one list into another. After the

* operation, the index of each copied element in the destination list

* will be identical to its index in the source list. The destination

* list's size must be greater than or equal to the source list's size.

* If it is greater, the remaining elements in the destination list are

* unaffected. <p>

*

* This method runs in linear time.

*

* @param <T> the class of the objects in the lists

* @param dest The destination list.

* @param src The source list.

* @throws IndexOutOfBoundsException if the destination list is too small

* to contain the entire source List.

* @throws UnsupportedOperationException if the destination list's

* list-iterator does not support the {@code set} operation.

*/

public static <T> void copy(List<? super T> dest, List<? extends T> src) {

int srcSize = src.size();

if (srcSize > dest.size())

throw new IndexOutOfBoundsException("Source does not fit in dest");

if (srcSize < COPY_THRESHOLD ||

(src instanceof RandomAccess && dest instanceof RandomAccess)) {

for (int i=0; i<srcSize; i++)

dest.set(i, src.get(i));

} else {

ListIterator<? super T> di=dest.listIterator();

ListIterator<? extends T> si=src.listIterator();

for (int i=0; i<srcSize; i++) {

di.next();

di.set(si.next());

}

}

}

/**

* Returns the minimum element of the given collection, according to the

* <i>natural ordering</i> of its elements. All elements in the

* collection must implement the {@code Comparable} interface.

* Furthermore, all elements in the collection must be <i>mutually

* comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a

* {@code ClassCastException} for any elements {@code e1} and

* {@code e2} in the collection).<p>

*

* This method iterates over the entire collection, hence it requires

* time proportional to the size of the collection.

*

* @param <T> the class of the objects in the collection

* @param coll the collection whose minimum element is to be determined.

* @return the minimum element of the given collection, according

* to the <i>natural ordering</i> of its elements.

* @throws ClassCastException if the collection contains elements that are

* not <i>mutually comparable</i> (for example, strings and

* integers).

* @throws NoSuchElementException if the collection is empty.

* @see Comparable

*/

public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {

Iterator<? extends T> i = coll.iterator();

T candidate = i.next();

while (i.hasNext()) {

T next = i.next();

if (next.compareTo(candidate) < 0)

candidate = next;

}

return candidate;

}

/**

* Returns the minimum element of the given collection, according to the

* order induced by the specified comparator. All elements in the

* collection must be <i>mutually comparable</i> by the specified

* comparator (that is, {@code comp.compare(e1, e2)} must not throw a

* {@code ClassCastException} for any elements {@code e1} and

* {@code e2} in the collection).<p>

*

* This method iterates over the entire collection, hence it requires

* time proportional to the size of the collection.

*

* @param <T> the class of the objects in the collection

* @param coll the collection whose minimum element is to be determined.

* @param comp the comparator with which to determine the minimum element.

* A {@code null} value indicates that the elements' <i>natural

* ordering</i> should be used.

* @return the minimum element of the given collection, according

* to the specified comparator.

* @throws ClassCastException if the collection contains elements that are

* not <i>mutually comparable</i> using the specified comparator.

* @throws NoSuchElementException if the collection is empty.

* @see Comparable

*/

@SuppressWarnings({"unchecked"})

public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {

if (comp==null)

return (T)min((Collection<Comparable<Object>>) coll);

Iterator<? extends T> i = coll.iterator();

T candidate = i.next();

while (i.hasNext()) {

T next = i.next();

if (comp.compare(next, candidate) < 0)

candidate = next;

}

return candidate;

}

/**

* Returns the maximum element of the given collection, according to the

* <i>natural ordering</i> of its elements. All elements in the

* collection must implement the {@code Comparable} interface.

* Furthermore, all elements in the collection must be <i>mutually

* comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a

* {@code ClassCastException} for any elements {@code e1} and

* {@code e2} in the collection).<p>

*

* This method iterates over the entire collection, hence it requires

* time proportional to the size of the collection.

*

* @param <T> the class of the objects in the collection

* @param coll the collection whose maximum element is to be determined.

* @return the maximum element of the given collection, according

* to the <i>natural ordering</i> of its elements.

* @throws ClassCastException if the collection contains elements that are

* not <i>mutually comparable</i> (for example, strings and

* integers).

* @throws NoSuchElementException if the collection is empty.

* @see Comparable

*/

public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {

Iterator<? extends T> i = coll.iterator();

T candidate = i.next();

while (i.hasNext()) {

T next = i.next();

if (next.compareTo(candidate) > 0)

candidate = next;

}

return candidate;

}

/**

* Returns the maximum element of the given collection, according to the

* order induced by the specified comparator. All elements in the

* collection must be <i>mutually comparable</i> by the specified

* comparator (that is, {@code comp.compare(e1, e2)} must not throw a

* {@code ClassCastException} for any elements {@code e1} and

* {@code e2} in the collection).<p>

*

* This method iterates over the entire collection, hence it requires

* time proportional to the size of the collection.

*

* @param <T> the class of the objects in the collection

* @param coll the collection whose maximum element is to be determined.

* @param comp the comparator with which to determine the maximum element.

* A {@code null} value indicates that the elements' <i>natural

* ordering</i> should be used.

* @return the maximum element of the given collection, according

* to the specified comparator.

* @throws ClassCastException if the collection contains elements that are

* not <i>mutually comparable</i> using the specified comparator.

* @throws NoSuchElementException if the collection is empty.

* @see Comparable

*/

@SuppressWarnings({"unchecked"})

public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {

if (comp==null)

return (T)max((Collection<Comparable<Object>>) coll);

Iterator<? extends T> i = coll.iterator();

T candidate = i.next();

while (i.hasNext()) {

T next = i.next();

if (comp.compare(next, candidate) > 0)

candidate = next;

}

return candidate;

}

/**

* Rotates the elements in the specified list by the specified distance.

* After calling this method, the element at index {@code i} will be

* the element previously at index {@code (i - distance)} mod

* {@code list.size()}, for all values of {@code i} between {@code 0}

* and {@code list.size()-1}, inclusive. (This method has no effect on

* the size of the list.)

*

* <p>For example, suppose {@code list} comprises{@code [t, a, n, k, s]}.

* After invoking {@code Collections.rotate(list, 1)} (or

* {@code Collections.rotate(list, -4)}), {@code list} will comprise

* {@code [s, t, a, n, k]}.

*

* <p>Note that this method can usefully be applied to sublists to

* move one or more elements within a list while preserving the

* order of the remaining elements. For example, the following idiom

* moves the element at index {@code j} forward to position

* {@code k} (which must be greater than or equal to {@code j}):

* <pre>

* Collections.rotate(list.subList(j, k+1), -1);

* </pre>

* To make this concrete, suppose {@code list} comprises

* {@code [a, b, c, d, e]}. To move the element at index {@code 1}

* ({@code b}) forward two positions, perform the following invocation:

* <pre>

* Collections.rotate(l.subList(1, 4), -1);

* </pre>

* The resulting list is {@code [a, c, d, b, e]}.

*

* <p>To move more than one element forward, increase the absolute value

* of the rotation distance. To move elements backward, use a positive

* shift distance.

*

* <p>If the specified list is small or implements the {@link

* RandomAccess} interface, this implementation exchanges the first

* element into the location it should go, and then repeatedly exchanges

* the displaced element into the location it should go until a displaced

* element is swapped into the first element. If necessary, the process

* is repeated on the second and successive elements, until the rotation

* is complete. If the specified list is large and doesn't implement the

* {@code RandomAccess} interface, this implementation breaks the

* list into two sublist views around index {@code -distance mod size}.

* Then the {@link #reverse(List)} method is invoked on each sublist view,

* and finally it is invoked on the entire list. For a more complete

* description of both algorithms, see Section 2.3 of Jon Bentley's

* <i>Programming Pearls</i> (Addison-Wesley, 1986).

*

* @param list the list to be rotated.

* @param distance the distance to rotate the list. There are no

* constraints on this value; it may be zero, negative, or

* greater than {@code list.size()}.

* @throws UnsupportedOperationException if the specified list or

* its list-iterator does not support the {@code set} operation.

* @since 1.4

*/

public static void rotate(List<?> list, int distance) {

if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)

rotate1(list, distance);

else

rotate2(list, distance);

}

private static <T> void rotate1(List<T> list, int distance) {

int size = list.size();

if (size == 0)

return;

distance = distance % size;

if (distance < 0)

distance += size;

if (distance == 0)

return;

int bound = size - distance;

for (int cycleStart = 0, nMoved = 0; nMoved < size; cycleStart++) {

T displaced = list.get(cycleStart);

int i = cycleStart;

do {

if (i >= bound)

i -= size;

i += distance;

displaced = list.set(i, displaced);

nMoved++;

} while (i != cycleStart);

}

}

private static void rotate2(List<?> list, int distance) {

int size = list.size();

if (size == 0)

return;

int mid = -distance % size;

if (mid < 0)

mid += size;

if (mid == 0)

return;

reverse(list.subList(0, mid));

reverse(list.subList(mid, size));

reverse(list);

}

/**

* Replaces all occurrences of one specified value in a list with another.

* More formally, replaces with {@code newVal} each element {@code e}

* in {@code list} such that

* {@code (oldVal==null ? e==null : oldVal.equals(e))}.

* (This method has no effect on the size of the list.)

*

* @param <T> the class of the objects in the list

* @param list the list in which replacement is to occur.

* @param oldVal the old value to be replaced.

* @param newVal the new value with which {@code oldVal} is to be

* replaced.

* @return {@code true} if {@code list} contained one or more elements

* {@code e} such that

* {@code (oldVal==null ? e==null : oldVal.equals(e))}.

* @throws UnsupportedOperationException if the specified list or

* its list-iterator does not support the {@code set} operation.

* @since 1.4

*/

public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {

boolean result = false;

int size = list.size();

if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {

if (oldVal==null) {

for (int i=0; i<size; i++) {

if (list.get(i)==null) {

list.set(i, newVal);

result = true;

}

}

} else {

for (int i=0; i<size; i++) {

if (oldVal.equals(list.get(i))) {

list.set(i, newVal);

result = true;

}

}

}

} else {

ListIterator<T> itr=list.listIterator();

if (oldVal==null) {

for (int i=0; i<size; i++) {

if (itr.next()==null) {

itr.set(newVal);

result = true;

}

}

} else {

for (int i=0; i<size; i++) {

if (oldVal.equals(itr.next())) {

itr.set(newVal);

result = true;

}

}

}

}

return result;

}

/**

* Returns the starting position of the first occurrence of the specified

* target list within the specified source list, or -1 if there is no

* such occurrence. More formally, returns the lowest index {@code i}

* such that {@code source.subList(i, i+target.size()).equals(target)},

* or -1 if there is no such index. (Returns -1 if

* {@code target.size() > source.size()})

*

* <p>This implementation uses the "brute force" technique of scanning

* over the source list, looking for a match with the target at each

* location in turn.

*

* @param source the list in which to search for the first occurrence

* of {@code target}.

* @param target the list to search for as a subList of {@code source}.

* @return the starting position of the first occurrence of the specified

* target list within the specified source list, or -1 if there

* is no such occurrence.

* @since 1.4

*/

public static int indexOfSubList(List<?> source, List<?> target) {

int sourceSize = source.size();

int targetSize = target.size();

int maxCandidate = sourceSize - targetSize;

if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||

(source instanceof RandomAccess&&target instanceof RandomAccess)) {

nextCand:

for (int candidate = 0; candidate <= maxCandidate; candidate++) {

for (int i=0, j=candidate; i<targetSize; i++, j++)

if (!eq(target.get(i), source.get(j)))

continue nextCand; // Element mismatch, try next cand

return candidate; // All elements of candidate matched target

}

} else { // Iterator version of above algorithm

ListIterator<?> si = source.listIterator();

nextCand:

for (int candidate = 0; candidate <= maxCandidate; candidate++) {

ListIterator<?> ti = target.listIterator();

for (int i=0; i<targetSize; i++) {

if (!eq(ti.next(), si.next())) {

// Back up source iterator to next candidate

for (int j=0; j<i; j++)

si.previous();

continue nextCand;

}

}

return candidate;

}

}

return -1; // No candidate matched the target

}

/**

* Returns the starting position of the last occurrence of the specified

* target list within the specified source list, or -1 if there is no such

* occurrence. More formally, returns the highest index {@code i}

* such that {@code source.subList(i, i+target.size()).equals(target)},

* or -1 if there is no such index. (Returns -1 if

* {@code target.size() > source.size()})

*

* <p>This implementation uses the "brute force" technique of iterating

* over the source list, looking for a match with the target at each

* location in turn.

*

* @param source the list in which to search for the last occurrence

* of {@code target}.

* @param target the list to search for as a subList of {@code source}.

* @return the starting position of the last occurrence of the specified

* target list within the specified source list, or -1 if there

* is no such occurrence.

* @since 1.4

*/

public static int lastIndexOfSubList(List<?> source, List<?> target) {

int sourceSize = source.size();

int targetSize = target.size();

int maxCandidate = sourceSize - targetSize;

if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||

source instanceof RandomAccess) { // Index access version

nextCand:

for (int candidate = maxCandidate; candidate >= 0; candidate--) {

for (int i=0, j=candidate; i<targetSize; i++, j++)

if (!eq(target.get(i), source.get(j)))

continue nextCand; // Element mismatch, try next cand

return candidate; // All elements of candidate matched target

}

} else { // Iterator version of above algorithm

if (maxCandidate < 0)

return -1;

ListIterator<?> si = source.listIterator(maxCandidate);

nextCand: