/*
* @(#)Collections.java 1.52 06/10/10
*
* Copyright 1990-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version
* 2 only, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License version 2 for more details (a copy is
* included at /legal/license.txt).
*
* You should have received a copy of the GNU General Public License
* version 2 along with this work; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 or visit www.sun.com if you need additional
* information or have any questions.
*
*/
package java.util;
import java.io.Serializable;
/**
* 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 <tt>NullPointerException</tt>
* if the collections 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 <tt>sort</tt> 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 <tt>UnsupportedOperationException</tt> if the collection does not
* support the appropriate mutation primitive(s), such as the <tt>set</tt>
* 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 <tt>sort</tt> method on an unmodifiable list that is
* already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
*
* <p>This class is a member of the
* <a href="{@docRoot}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @version 1.45, 02/17/00
* @see Collection
* @see Set
* @see List
* @see Map
* @since 1.2
*/
public 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
* <i>natural ordering</i> of its elements. All elements in the list must
* implement the <tt>Comparable</tt> interface. Furthermore, all elements
* in the list 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 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.<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.
*
* This implementation dumps the specified list into an array, sorts
* the array, and iterates over the list resetting each element
* from the corresponding position in the array. This avoids the
* n<sup>2</sup> log(n) performance that would result from attempting
* to sort a linked list in place.
*
* @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 <tt>set</tt> operation.
* @see Comparable
*/
public static void sort(List list) {
Object a[] = list.toArray();
Arrays.sort(a);
ListIterator i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set(a[j]);
}
}
/**
* 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,
* <tt>c.compare(e1, e2)</tt> must not throw a <tt>ClassCastException</tt>
* for any elements <tt>e1</tt> and <tt>e2</tt> 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 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.
*
* The specified list must be modifiable, but need not be resizable.
* This implementation dumps the specified list into an array, sorts
* the array, and iterates over the list resetting each element
* from the corresponding position in the array. This avoids the
* n<sup>2</sup> log(n) performance that would result from attempting
* to sort a linked list in place.
*
* @param list the list to be sorted.
* @param c the comparator to determine the order of the list. A
* <tt>null</tt> 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 <tt>set</tt> operation.
* @see Comparator
*/
public static void sort(List list, Comparator c) {
Object a[] = list.toArray();
Arrays.sort(a, c);
ListIterator i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set(a[j]);
}
}
/**
* Searches the specified list for the specified object using the binary
* search algorithm. The list must be sorted into ascending order
* according to the <i>natural ordering</i> of its elements (as by the
* <tt>sort(List)</tt> method, above) 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} 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 list the list to be searched.
* @param key the key to be searched for.
* @return index of the search key, if it is contained in the list;
* otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. 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 <tt>list.size()</tt>, if all
* elements in the list are less than the specified key. Note
* that this guarantees that the return value will be >= 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 in not mutually comparable
* with the elements of the list.
* @see Comparable
* @see #sort(List)
*/
public static int binarySearch(List list, Object key) {
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return indexedBinarySearch(list, key);
else
return iteratorBinarySearch(list, key);
}
private static int indexedBinarySearch(List list, Object key) {
int low = 0;
int high = list.size()-1;
while (low <= high) {
int mid = (low + high) >> 1;
Object midVal = list.get(mid);
int cmp = ((Comparable)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 int iteratorBinarySearch(List list, Object key) {
int low = 0;
int high = list.size()-1;
ListIterator i = list.listIterator();
while (low <= high) {
int mid = (low + high) >> 1;
Object midVal = get(i, mid);
int cmp = ((Comparable)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 Object get(ListIterator i, int index) {
Object obj = null;
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 <tt>Sort(List,
* Comparator)</tt> method, above), 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} and is large, this
* this method will do an iterator-based binary search that performs
* O(n) link traversals and O(log n) element comparisons.
*
* @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
* <tt>null</tt> value indicates that the elements' <i>natural
* ordering</i> should be used.
* @return index of the search key, if it is contained in the list;
* otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>. 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 <tt>list.size()</tt>, if all
* elements in the list are less than the specified key. Note
* that this guarantees that the return value will be >= 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 in not mutually comparable with the
* elements of the list using this comparator.
* @see Comparable
* @see #sort(List, Comparator)
*/
public static int binarySearch(List list, Object key, Comparator c) {
if (c==null)
return binarySearch(list, key);
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return indexedBinarySearch(list, key, c);
else
return iteratorBinarySearch(list, key, c);
}
private static int indexedBinarySearch(List l, Object key, Comparator c) {
int low = 0;
int high = l.size()-1;
while (low <= high) {
int mid = (low + high) >> 1;
Object 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 int iteratorBinarySearch(List l, Object key, Comparator c) {
int low = 0;
int high = l.size()-1;
ListIterator i = l.listIterator();
while (low <= high) {
int mid = (low + high) >> 1;
Object 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.
*
* @param list the list whose elements are to be reversed.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> method.
*/
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 {
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 randomenss 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.<p>
*
* 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 <tt>set</tt> method.
*/
public static void shuffle(List list) {
shuffle(list, r);
}
private static Random r = new Random();
/**
* 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.<p>
*
* 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 <tt>set</tt> operation.
*/
public static void shuffle(List list, Random 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
ListIterator it = list.listIterator();
for (int i=0; i<arr.length; i++) {
it.next();
it.set(arr[i]);
}
}
}
/**
* 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 <tt>i</tt> or <tt>j</tt>
* is out of range (i < 0 || i >= list.size()
* || j < 0 || j >= list.size()).
* @since 1.4
*/
public static void swap(List list, int i, int j) {
list.set(i, list.set(j, list.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 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 <tt>set</tt> operation.
*/
public static void fill(List list, Object 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 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 must be at least as long as the source list. If it is longer, the
* remaining elements in the destination list are unaffected. <p>
*
* This method runs in linear time.
*
* @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 <tt>set</tt> operation.
*/
public static void copy(List dest, List 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 di=dest.listIterator(), 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 <tt>Comparable</tt> interface.
* Furthermore, all elements in the collection 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 collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of 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 Object min(Collection coll) {
Iterator i = coll.iterator();
Comparable candidate = (Comparable)(i.next());
while(i.hasNext()) {
Comparable next = (Comparable)(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, <tt>comp.compare(e1, e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of 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 <tt>null</tt> 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
*/
public static Object min(Collection coll, Comparator comp) {
if (comp==null)
return min(coll);
Iterator i = coll.iterator();
Object candidate = i.next();
while(i.hasNext()) {
Object 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 <tt>Comparable</tt> interface.
* Furthermore, all elements in the collection 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 collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of 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 Object max(Collection coll) {
Iterator i = coll.iterator();
Comparable candidate = (Comparable)(i.next());
while(i.hasNext()) {
Comparable next = (Comparable)(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, <tt>comp.compare(e1, e2)</tt> must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
* <tt>e2</tt> in the collection).<p>
*
* This method iterates over the entire collection, hence it requires
* time proportional to the size of 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 <tt>null</tt> 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
*/
public static Object max(Collection coll, Comparator comp) {
if (comp==null)
return max(coll);
Iterator i = coll.iterator();
Object candidate = i.next();
while(i.hasNext()) {
Object 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 <tt>i</tt> will be
* the element previously at index <tt>(i - distance)</tt> mod
* <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
* and <tt>list.size()-1</tt>, inclusive. (This method has no effect on
* the size of the list.)
*
* <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
* After invoking <tt>Collections.rotate(list, 1)</tt> (or
* <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
* <tt>[s, t, a, n, k]</tt>.
*
* <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 <tt>j</tt> forward to position
* <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
* <pre>
* Collections.rotate(list.subList(j, k+1), -1);
* </pre>
* To make this concrete, suppose <tt>list</tt> comprises
* <tt>[a, b, c, d, e]</tt>. To move the element at index <tt>1</tt>
* (<tt>b</tt>) forward two positions, perform the following invocation:
* <pre>
* Collections.rotate(l.subList(1, 4), -1);
* </pre>
* The resulting list is <tt>[a, c, d, b, e]</tt>.
*
* <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
* <tt>RandomAccess</tt> interface, this implementation breaks the
* list into two sublist views around index <tt>-distance mod size</tt>.
* 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 <tt>list.size()</tt>.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> method.
* @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 void rotate1(List list, int distance) {
int size = list.size();
if (size == 0)
return;
distance = distance % size;
if (distance < 0)
distance += size;
if (distance == 0)
return;
for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
Object displaced = list.get(cycleStart);
int i = cycleStart;
do {
i += distance;
if (i >= size)
i -= size;
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;
Collections.reverse(list.subList(0, mid));
Collections.reverse(list.subList(mid, size));
Collections.reverse(list);
}
/**
* Replaces all occurrences of one specified value in a list with another.
* More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
* in <tt>list</tt> such that
* <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
* (This method has no effect on the size of 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 <tt>oldVal</tt> is to be
* replaced.
* @return <tt>true</tt> if <tt>list</tt> contained one or more elements
* <tt>e</tt> such that
* <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
* @throws UnsupportedOperationException if the specified list or
* its list-iterator does not support the <tt>set</tt> method.
* @since 1.4
*/
public static boolean replaceAll(List list, Object oldVal, Object 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 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 the lowest index <tt>i</tt>
* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
* or -1 if there is no such index. (Returns -1 if
* <tt>target.size() > source.size()</tt>.)
*
* <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 <tt>target</tt>.
* @param target the list to search for as a subList of <tt>source</tt>.
* @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 the highest index <tt>i</tt>
* such that <tt>source.subList(i, i+target.size()).equals(target)</tt>,
* or -1 if there is no such index. (Returns -1 if
* <tt>target.size() > source.size()</tt>.)
*
* <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 <tt>target</tt>.
* @param target the list to search for as a subList of <tt>source</tt>.
* @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:
for (int candidate = maxCandidate; candidate >= 0; candidate--) {
ListIterator ti = target.listIterator();
for (int i=0; i<targetSize; i++) {
if (!eq(ti.next(), si.next())) {
if (candidate != 0) {
// Back up source iterator to next candidate
for (int j=0; j<=i+1; j++)
si.previous();
}
continue nextCand;
}
}
return candidate;
}
}
return -1; // No candidate matched the target
}
// Unmodifiable Wrappers
/**
* Returns an unmodifiable view of the specified collection. This method
* allows modules to provide users with "read-only" access to internal
* collections. Query operations on the returned collection "read through"
* to the specified collection, and attempts to modify the returned
* collection, whether direct or via its iterator, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned collection does <i>not</i> pass the hashCode and equals
* operations through to the backing collection, but relies on
* <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods. This
* is necessary to preserve the contracts of these operations in the case
* that the backing collection is a set or a list.<p>
*
* The returned collection will be serializable if the specified collection
* is serializable.
*
* @param c the collection for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified collection.
*/
public static Collection unmodifiableCollection(Collection c) {
return new UnmodifiableCollection(c);
}
/**
* @serial include
*/
static class UnmodifiableCollection implements Collection, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1820017752578914078L;
Collection c;
UnmodifiableCollection(Collection c) {
if (c==null)
throw new NullPointerException();
this.c = c;
}
public int size() {return c.size();}
public boolean isEmpty() {return c.isEmpty();}
public boolean contains(Object o) {return c.contains(o);}
public Object[] toArray() {return c.toArray();}
public Object[] toArray(Object[] a) {return c.toArray(a);}
public String toString() {return c.toString();}
public Iterator iterator() {
return new Iterator() {
Iterator i = c.iterator();
public boolean hasNext() {return i.hasNext();}
public Object next() {return i.next();}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public boolean add(Object o){
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public boolean containsAll(Collection coll) {
return c.containsAll(coll);
}
public boolean addAll(Collection coll) {
throw new UnsupportedOperationException();
}
public boolean removeAll(Collection coll) {
throw new UnsupportedOperationException();
}
public boolean retainAll(Collection coll) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
}
/**
* Returns an unmodifiable view of the specified set. This method allows
* modules to provide users with "read-only" access to internal sets.
* Query operations on the returned set "read through" to the specified
* set, and attempts to modify the returned set, whether direct or via its
* iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned set will be serializable if the specified set
* is serializable.
*
* @param s the set for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified set.
*/
public static Set unmodifiableSet(Set s) {
return new UnmodifiableSet(s);
}
/**
* @serial include
*/
static class UnmodifiableSet extends UnmodifiableCollection
implements Set, Serializable {
UnmodifiableSet(Set s) {super(s);}
public boolean equals(Object o) {return c.equals(o);}
public int hashCode() {return c.hashCode();}
}
/**
* Returns an unmodifiable view of the specified sorted set. This method
* allows modules to provide users with "read-only" access to internal
* sorted sets. Query operations on the returned sorted set "read
* through" to the specified sorted set. Attempts to modify the returned
* sorted set, whether direct, via its iterator, or via its
* <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
* an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned sorted set will be serializable if the specified sorted set
* is serializable.
*
* @param s the sorted set for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified sorted set.
*/
public static SortedSet unmodifiableSortedSet(SortedSet s) {
return new UnmodifiableSortedSet(s);
}
/**
* @serial include
*/
static class UnmodifiableSortedSet extends UnmodifiableSet
implements SortedSet, Serializable {
private SortedSet ss;
UnmodifiableSortedSet(SortedSet s) {super(s); ss = s;}
public Comparator comparator() {return ss.comparator();}
public SortedSet subSet(Object fromElement, Object toElement) {
return new UnmodifiableSortedSet(ss.subSet(fromElement,toElement));
}
public SortedSet headSet(Object toElement) {
return new UnmodifiableSortedSet(ss.headSet(toElement));
}
public SortedSet tailSet(Object fromElement) {
return new UnmodifiableSortedSet(ss.tailSet(fromElement));
}
public Object first() {return ss.first();}
public Object last() {return ss.last();}
}
/**
* Returns an unmodifiable view of the specified list. This method allows
* modules to provide users with "read-only" access to internal
* lists. Query operations on the returned list "read through" to the
* specified list, and attempts to modify the returned list, whether
* direct or via its iterator, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned list will be serializable if the specified list
* is serializable. Similarly, the returned list will implement
* {@link RandomAccess} if the specified list does.
* the
*
* @param list the list for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified list.
*/
public static List unmodifiableList(List list) {
return (list instanceof RandomAccess ?
new UnmodifiableRandomAccessList(list) :
new UnmodifiableList(list));
}
/**
* @serial include
*/
static class UnmodifiableList extends UnmodifiableCollection
implements List {
static final long serialVersionUID = -283967356065247728L;
List list;
UnmodifiableList(List list) {
super(list);
this.list = list;
}
public boolean equals(Object o) {return list.equals(o);}
public int hashCode() {return list.hashCode();}
public Object get(int index) {return list.get(index);}
public Object set(int index, Object element) {
throw new UnsupportedOperationException();
}
public void add(int index, Object element) {
throw new UnsupportedOperationException();
}
public Object remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {return list.indexOf(o);}
public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
public boolean addAll(int index, Collection c) {
throw new UnsupportedOperationException();
}
public ListIterator listIterator() {return listIterator(0);}
public ListIterator listIterator(final int index) {
return new ListIterator() {
ListIterator i = list.listIterator(index);
public boolean hasNext() {return i.hasNext();}
public Object next() {return i.next();}
public boolean hasPrevious() {return i.hasPrevious();}
public Object previous() {return i.previous();}
public int nextIndex() {return i.nextIndex();}
public int previousIndex() {return i.previousIndex();}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(Object o) {
throw new UnsupportedOperationException();
}
public void add(Object o) {
throw new UnsupportedOperationException();
}
};
}
public List subList(int fromIndex, int toIndex) {
return new UnmodifiableList(list.subList(fromIndex, toIndex));
}
/**
* UnmodifiableRandomAccessList instances are serialized as
* UnmodifiableList instances to allow them to be deserialized
* in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
* This method inverts the transformation. As a beneficial
* side-effect, it also grafts the RandomAccess marker onto
* UnmodifiableList instances that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, UnmodifiableRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* UnmodifiableList instances, as this method was missing in 1.4.
*/
private Object readResolve() {
return (list instanceof RandomAccess ?
new UnmodifiableRandomAccessList(list) : this);
}
}
/**
* @serial include
*/
static class UnmodifiableRandomAccessList extends UnmodifiableList
implements RandomAccess
{
UnmodifiableRandomAccessList(List list) {
super(list);
}
public List subList(int fromIndex, int toIndex) {
return new UnmodifiableRandomAccessList(
list.subList(fromIndex, toIndex));
}
private static final long serialVersionUID = -2542308836966382001L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do
* not have UnmodifiableRandomAccessList). UnmodifiableList has
* a readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new UnmodifiableList(list);
}
}
/**
* Returns an unmodifiable view of the specified map. This method
* allows modules to provide users with "read-only" access to internal
* maps. Query operations on the returned map "read through"
* to the specified map, and attempts to modify the returned
* map, whether direct or via its collection views, result in an
* <tt>UnsupportedOperationException</tt>.<p>
*
* The returned map will be serializable if the specified map
* is serializable.
*
* @param m the map for which an unmodifiable view is to be returned.
* @return an unmodifiable view of the specified map.
*/
public static Map unmodifiableMap(Map m) {
return new UnmodifiableMap(m);
}
/**
* @serial include
*/
private static class UnmodifiableMap implements Map, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = -1034234728574286014L;
private final Map m;
UnmodifiableMap(Map m) {
if (m==null)
throw new NullPointerException();
this.m = m;
}
public int size() {return m.size();}
public boolean isEmpty() {return m.isEmpty();}
public boolean containsKey(Object key) {return m.containsKey(key);}
public boolean containsValue(Object val) {return m.containsValue(val);}
public Object get(Object key) {return m.get(key);}
public Object put(Object key, Object value) {
throw new UnsupportedOperationException();
}
public Object remove(Object key) {
throw new UnsupportedOperationException();
}
public void putAll(Map t) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
private transient Set keySet = null;
private transient Set entrySet = null;
private transient Collection values = null;
public Set keySet() {
if (keySet==null)
keySet = unmodifiableSet(m.keySet());
return keySet;
}
public Set entrySet() {
if (entrySet==null)
entrySet = new UnmodifiableEntrySet(m.entrySet());
return entrySet;
}
public Collection values() {
if (values==null)
values = unmodifiableCollection(m.values());
return values;
}
public boolean equals(Object o) {return m.equals(o);}
public int hashCode() {return m.hashCode();}
public String toString() {return m.toString();}
/**
* We need this class in addition to UnmodifiableSet as
* Map.Entries themselves permit modification of the backing Map
* via their setValue operation. This class is subtle: there are
* many possible attacks that must be thwarted.
*
* @serial include
*/
static class UnmodifiableEntrySet extends UnmodifiableSet {
UnmodifiableEntrySet(Set s) {
super(s);
}
public Iterator iterator() {
return new Iterator() {
Iterator i = c.iterator();
public boolean hasNext() {
return i.hasNext();
}
public Object next() {
return new UnmodifiableEntry((Map.Entry)i.next());
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public Object[] toArray() {
Object[] a = c.toArray();
for (int i=0; i<a.length; i++)
a[i] = new UnmodifiableEntry((Map.Entry)a[i]);
return a;
}
public Object[] toArray(Object a[]) {
// We don't pass a to c.toArray, to avoid window of
// vulnerability wherein an unscrupulous multithreaded client
// could get his hands on raw (unwrapped) Entries from c.
Object[] arr = c.toArray(a.length==0 ? a :
(Object[])java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), 0));
for (int i=0; i<arr.length; i++)
arr[i] = new UnmodifiableEntry((Map.Entry)arr[i]);
if (arr.length > a.length)
return arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
/**
* This method is overridden to protect the backing set against
* an object with a nefarious equals function that senses
* that the equality-candidate is Map.Entry and calls its
* setValue method.
*/
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return c.contains(new UnmodifiableEntry((Map.Entry)o));
}
/**
* The next two methods are overridden to protect against
* an unscrupulous List whose contains(Object o) method senses
* when o is a Map.Entry, and calls o.setValue.
*/
public boolean containsAll(Collection coll) {
Iterator e = coll.iterator();
while (e.hasNext())
if(!contains(e.next())) // Invokes safe contains() above
return false;
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set s = (Set) o;
if (s.size() != c.size())
return false;
return containsAll(s); // Invokes safe containsAll() above
}
/**
* This "wrapper class" serves two purposes: it prevents
* the client from modifying the backing Map, by short-circuiting
* the setValue method, and it protects the backing Map against
* an ill-behaved Map.Entry that attempts to modify another
* Map Entry when asked to perform an equality check.
*/
private static class UnmodifiableEntry implements Map.Entry {
private Map.Entry e;
UnmodifiableEntry(Map.Entry e) {this.e = e;}
public Object getKey() {return e.getKey();}
public Object getValue() {return e.getValue();}
public Object setValue(Object value) {
throw new UnsupportedOperationException();
}
public int hashCode() {return e.hashCode();}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry)o;
return eq(e.getKey(), t.getKey()) &&
eq(e.getValue(), t.getValue());
}
public String toString() {return e.toString();}
}
}
}
/**
* Returns an unmodifiable view of the specified sorted map. This method
* allows modules to provide users with "read-only" access to internal
* sorted maps. Query operations on the returned sorted map "read through"
* to the specified sorted map. Attempts to modify the returned
* sorted map, whether direct, via its collection views, or via its
* <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
* an <tt>UnsupportedOperationException</tt>.<p>
*
* The returned sorted map will be serializable if the specified sorted map
* is serializable.
*
* @param m the sorted map for which an unmodifiable view is to be
* returned.
* @return an unmodifiable view of the specified sorted map.
*/
public static SortedMap unmodifiableSortedMap(SortedMap m) {
return new UnmodifiableSortedMap(m);
}
/**
* @serial include
*/
static class UnmodifiableSortedMap extends UnmodifiableMap
implements SortedMap, Serializable {
private SortedMap sm;
UnmodifiableSortedMap(SortedMap m) {super(m); sm = m;}
public Comparator comparator() {return sm.comparator();}
public SortedMap subMap(Object fromKey, Object toKey) {
return new UnmodifiableSortedMap(sm.subMap(fromKey, toKey));
}
public SortedMap headMap(Object toKey) {
return new UnmodifiableSortedMap(sm.headMap(toKey));
}
public SortedMap tailMap(Object fromKey) {
return new UnmodifiableSortedMap(sm.tailMap(fromKey));
}
public Object firstKey() {return sm.firstKey();}
public Object lastKey() {return sm.lastKey();}
}
// Synch Wrappers
/**
* Returns a synchronized (thread-safe) collection backed by the specified
* collection. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing collection is accomplished
* through the returned collection.<p>
*
* It is imperative that the user manually synchronize on the returned
* collection when iterating over it:
* <pre>
* Collection c = Collections.synchronizedCollection(myCollection);
* ...
* synchronized(c) {
* Iterator i = c.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned collection does <i>not</i> pass the <tt>hashCode</tt>
* and <tt>equals</tt> operations through to the backing collection, but
* relies on <tt>Object</tt>'s equals and hashCode methods. This is
* necessary to preserve the contracts of these operations in the case
* that the backing collection is a set or a list.<p>
*
* The returned collection will be serializable if the specified collection
* is serializable.
*
* @param c the collection to be "wrapped" in a synchronized collection.
* @return a synchronized view of the specified collection.
*/
public static Collection synchronizedCollection(Collection c) {
return new SynchronizedCollection(c);
}
static Collection synchronizedCollection(Collection c, Object mutex) {
return new SynchronizedCollection(c, mutex);
}
/**
* @serial include
*/
static class SynchronizedCollection implements Collection, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 3053995032091335093L;
Collection c; // Backing Collection
Object mutex; // Object on which to synchronize
SynchronizedCollection(Collection c) {
if (c==null)
throw new NullPointerException();
this.c = c;
mutex = this;
}
SynchronizedCollection(Collection c, Object mutex) {
this.c = c;
this.mutex = mutex;
}
public int size() {
synchronized(mutex) {return c.size();}
}
public boolean isEmpty() {
synchronized(mutex) {return c.isEmpty();}
}
public boolean contains(Object o) {
synchronized(mutex) {return c.contains(o);}
}
public Object[] toArray() {
synchronized(mutex) {return c.toArray();}
}
public Object[] toArray(Object[] a) {
synchronized(mutex) {return c.toArray(a);}
}
public Iterator iterator() {
return c.iterator(); // Must be manually synched by user!
}
public boolean add(Object o) {
synchronized(mutex) {return c.add(o);}
}
public boolean remove(Object o) {
synchronized(mutex) {return c.remove(o);}
}
public boolean containsAll(Collection coll) {
synchronized(mutex) {return c.containsAll(coll);}
}
public boolean addAll(Collection coll) {
synchronized(mutex) {return c.addAll(coll);}
}
public boolean removeAll(Collection coll) {
synchronized(mutex) {return c.removeAll(coll);}
}
public boolean retainAll(Collection coll) {
synchronized(mutex) {return c.retainAll(coll);}
}
public void clear() {
synchronized(mutex) {c.clear();}
}
public String toString() {
synchronized(mutex) {return c.toString();}
}
}
/**
* Returns a synchronized (thread-safe) set backed by the specified
* set. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing set is accomplished
* through the returned set.<p>
*
* It is imperative that the user manually synchronize on the returned
* set when iterating over it:
* <pre>
* Set s = Collections.synchronizedSet(new HashSet());
* ...
* synchronized(s) {
* Iterator i = s.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned set will be serializable if the specified set is
* serializable.
*
* @param s the set to be "wrapped" in a synchronized set.
* @return a synchronized view of the specified set.
*/
public static Set synchronizedSet(Set s) {
return new SynchronizedSet(s);
}
static Set synchronizedSet(Set s, Object mutex) {
return new SynchronizedSet(s, mutex);
}
/**
* @serial include
*/
static class SynchronizedSet extends SynchronizedCollection
implements Set {
SynchronizedSet(Set s) {
super(s);
}
SynchronizedSet(Set s, Object mutex) {
super(s, mutex);
}
public boolean equals(Object o) {
synchronized(mutex) {return c.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return c.hashCode();}
}
}
/**
* Returns a synchronized (thread-safe) sorted set backed by the specified
* sorted set. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing sorted set is accomplished
* through the returned sorted set (or its views).<p>
*
* It is imperative that the user manually synchronize on the returned
* sorted set when iterating over it or any of its <tt>subSet</tt>,
* <tt>headSet</tt>, or <tt>tailSet</tt> views.
* <pre>
* SortedSet s = Collections.synchronizedSortedSet(new HashSortedSet());
* ...
* synchronized(s) {
* Iterator i = s.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* or:
* <pre>
* SortedSet s = Collections.synchronizedSortedSet(new HashSortedSet());
* SortedSet s2 = s.headSet(foo);
* ...
* synchronized(s) { // Note: s, not s2!!!
* Iterator i = s2.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned sorted set will be serializable if the specified
* sorted set is serializable.
*
* @param s the sorted set to be "wrapped" in a synchronized sorted set.
* @return a synchronized view of the specified sorted set.
*/
public static SortedSet synchronizedSortedSet(SortedSet s) {
return new SynchronizedSortedSet(s);
}
/**
* @serial include
*/
static class SynchronizedSortedSet extends SynchronizedSet
implements SortedSet
{
private SortedSet ss;
SynchronizedSortedSet(SortedSet s) {
super(s);
ss = s;
}
SynchronizedSortedSet(SortedSet s, Object mutex) {
super(s, mutex);
ss = s;
}
public Comparator comparator() {
synchronized(mutex) {return ss.comparator();}
}
public SortedSet subSet(Object fromElement, Object toElement) {
synchronized(mutex) {
return new SynchronizedSortedSet(
ss.subSet(fromElement, toElement), mutex);
}
}
public SortedSet headSet(Object toElement) {
synchronized(mutex) {
return new SynchronizedSortedSet(ss.headSet(toElement), mutex);
}
}
public SortedSet tailSet(Object fromElement) {
synchronized(mutex) {
return new SynchronizedSortedSet(ss.tailSet(fromElement),mutex);
}
}
public Object first() {
synchronized(mutex) {return ss.first();}
}
public Object last() {
synchronized(mutex) {return ss.last();}
}
}
/**
* Returns a synchronized (thread-safe) list backed by the specified
* list. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing list is accomplished
* through the returned list.<p>
*
* It is imperative that the user manually synchronize on the returned
* list when iterating over it:
* <pre>
* List list = Collections.synchronizedList(new ArrayList());
* ...
* synchronized(list) {
* Iterator i = list.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned list will be serializable if the specified list is
* serializable.
*
* @param list the list to be "wrapped" in a synchronized list.
* @return a synchronized view of the specified list.
*/
public static List synchronizedList(List list) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList(list) :
new SynchronizedList(list));
}
static List synchronizedList(List list, Object mutex) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList(list, mutex) :
new SynchronizedList(list, mutex));
}
/**
* @serial include
*/
static class SynchronizedList extends SynchronizedCollection
implements List {
static final long serialVersionUID = -7754090372962971524L;
List list;
SynchronizedList(List list) {
super(list);
this.list = list;
}
SynchronizedList(List list, Object mutex) {
super(list, mutex);
this.list = list;
}
public boolean equals(Object o) {
synchronized(mutex) {return list.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return list.hashCode();}
}
public Object get(int index) {
synchronized(mutex) {return list.get(index);}
}
public Object set(int index, Object element) {
synchronized(mutex) {return list.set(index, element);}
}
public void add(int index, Object element) {
synchronized(mutex) {list.add(index, element);}
}
public Object remove(int index) {
synchronized(mutex) {return list.remove(index);}
}
public int indexOf(Object o) {
synchronized(mutex) {return list.indexOf(o);}
}
public int lastIndexOf(Object o) {
synchronized(mutex) {return list.lastIndexOf(o);}
}
public boolean addAll(int index, Collection c) {
synchronized(mutex) {return list.addAll(index, c);}
}
public ListIterator listIterator() {
return list.listIterator(); // Must be manually synched by user
}
public ListIterator listIterator(int index) {
return list.listIterator(index); // Must be manually synched by usr
}
public List subList(int fromIndex, int toIndex) {
synchronized(mutex) {
return new SynchronizedList(list.subList(fromIndex, toIndex),
mutex);
}
}
/**
* SynchronizedRandomAccessList instances are serialized as
* SynchronizedList instances to allow them to be deserialized
* in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
* This method inverts the transformation. As a beneficial
* side-effect, it also grafts the RandomAccess marker onto
* SynchronizedList instances that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, SynchronizedRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* SynchronizedList instances, as this method was missing in 1.4.
*/
private Object readResolve() {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList(list) : this);
}
}
/**
* @serial include
*/
static class SynchronizedRandomAccessList extends SynchronizedList
implements RandomAccess
{
SynchronizedRandomAccessList(List list) {
super(list);
}
SynchronizedRandomAccessList(List list, Object mutex) {
super(list, mutex);
}
public List subList(int fromIndex, int toIndex) {
synchronized(mutex) {
return new SynchronizedRandomAccessList(
list.subList(fromIndex, toIndex), mutex);
}
}
static final long serialVersionUID = 1530674583602358482L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do
* not have SynchronizedRandomAccessList). SynchronizedList has
* a readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new SynchronizedList(list);
}
}
/**
* Returns a synchronized (thread-safe) map backed by the specified
* map. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing map is accomplished
* through the returned map.<p>
*
* It is imperative that the user manually synchronize on the returned
* map when iterating over any of its collection views:
* <pre>
* Map m = Collections.synchronizedMap(new HashMap());
* ...
* Set s = m.keySet(); // Needn't be in synchronized block
* ...
* synchronized(m) { // Synchronizing on m, not s!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned map will be serializable if the specified map is
* serializable.
*
* @param m the map to be "wrapped" in a synchronized map.
* @return a synchronized view of the specified map.
*/
public static Map synchronizedMap(Map m) {
return new SynchronizedMap(m);
}
/**
* @serial include
*/
private static class SynchronizedMap implements Map, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1978198479659022715L;
private Map m; // Backing Map
Object mutex; // Object on which to synchronize
SynchronizedMap(Map m) {
if (m==null)
throw new NullPointerException();
this.m = m;
mutex = this;
}
SynchronizedMap(Map m, Object mutex) {
this.m = m;
this.mutex = mutex;
}
public int size() {
synchronized(mutex) {return m.size();}
}
public boolean isEmpty(){
synchronized(mutex) {return m.isEmpty();}
}
public boolean containsKey(Object key) {
synchronized(mutex) {return m.containsKey(key);}
}
public boolean containsValue(Object value){
synchronized(mutex) {return m.containsValue(value);}
}
public Object get(Object key) {
synchronized(mutex) {return m.get(key);}
}
public Object put(Object key, Object value) {
synchronized(mutex) {return m.put(key, value);}
}
public Object remove(Object key) {
synchronized(mutex) {return m.remove(key);}
}
public void putAll(Map map) {
synchronized(mutex) {m.putAll(map);}
}
public void clear() {
synchronized(mutex) {m.clear();}
}
private transient Set keySet = null;
private transient Set entrySet = null;
private transient Collection values = null;
public Set keySet() {
synchronized(mutex) {
if (keySet==null)
keySet = new SynchronizedSet(m.keySet(), mutex);
return keySet;
}
}
public Set entrySet() {
synchronized(mutex) {
if (entrySet==null)
entrySet = new SynchronizedSet(m.entrySet(), mutex);
return entrySet;
}
}
public Collection values() {
synchronized(mutex) {
if (values==null)
values = new SynchronizedCollection(m.values(), mutex);
return values;
}
}
public boolean equals(Object o) {
synchronized(mutex) {return m.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return m.hashCode();}
}
public String toString() {
synchronized(mutex) {return m.toString();}
}
}
/**
* Returns a synchronized (thread-safe) sorted map backed by the specified
* sorted map. In order to guarantee serial access, it is critical that
* <strong>all</strong> access to the backing sorted map is accomplished
* through the returned sorted map (or its views).<p>
*
* It is imperative that the user manually synchronize on the returned
* sorted map when iterating over any of its collection views, or the
* collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
* <tt>tailMap</tt> views.
* <pre>
* SortedMap m = Collections.synchronizedSortedMap(new HashSortedMap());
* ...
* Set s = m.keySet(); // Needn't be in synchronized block
* ...
* synchronized(m) { // Synchronizing on m, not s!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* or:
* <pre>
* SortedMap m = Collections.synchronizedSortedMap(new HashSortedMap());
* SortedMap m2 = m.subMap(foo, bar);
* ...
* Set s2 = m2.keySet(); // Needn't be in synchronized block
* ...
* synchronized(m) { // Synchronizing on m, not m2 or s2!
* Iterator i = s.iterator(); // Must be in synchronized block
* while (i.hasNext())
* foo(i.next());
* }
* </pre>
* Failure to follow this advice may result in non-deterministic behavior.
*
* <p>The returned sorted map will be serializable if the specified
* sorted map is serializable.
*
* @param m the sorted map to be "wrapped" in a synchronized sorted map.
* @return a synchronized view of the specified sorted map.
*/
public static SortedMap synchronizedSortedMap(SortedMap m) {
return new SynchronizedSortedMap(m);
}
/**
* @serial include
*/
static class SynchronizedSortedMap extends SynchronizedMap
implements SortedMap
{
private SortedMap sm;
SynchronizedSortedMap(SortedMap m) {
super(m);
sm = m;
}
SynchronizedSortedMap(SortedMap m, Object mutex) {
super(m, mutex);
sm = m;
}
public Comparator comparator() {
synchronized(mutex) {return sm.comparator();}
}
public SortedMap subMap(Object fromKey, Object toKey) {
synchronized(mutex) {
return new SynchronizedSortedMap(
sm.subMap(fromKey, toKey), mutex);
}
}
public SortedMap headMap(Object toKey) {
synchronized(mutex) {
return new SynchronizedSortedMap(sm.headMap(toKey), mutex);
}
}
public SortedMap tailMap(Object fromKey) {
synchronized(mutex) {
return new SynchronizedSortedMap(sm.tailMap(fromKey),mutex);
}
}
public Object firstKey() {
synchronized(mutex) {return sm.firstKey();}
}
public Object lastKey() {
synchronized(mutex) {return sm.lastKey();}
}
}
// Miscellaneous
/**
* The empty set (immutable). This set is serializable.
*/
public static final Set EMPTY_SET = new EmptySet();
/**
* @serial include
*/
private static class EmptySet extends AbstractSet implements Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1582296315990362920L;
public Iterator iterator() {
return new Iterator() {
public boolean hasNext() {
return false;
}
public Object next() {
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public int size() {return 0;}
public boolean contains(Object obj) {return false;}
// Preserves singleton property
private Object readResolve() {
return EMPTY_SET;
}
}
/**
* The empty list (immutable). This list is serializable.
*/
public static final List EMPTY_LIST = new EmptyList();
/**
* @serial include
*/
private static class EmptyList extends AbstractList
implements RandomAccess, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 8842843931221139166L;
public int size() {return 0;}
public boolean contains(Object obj) {return false;}
public Object get(int index) {
throw new IndexOutOfBoundsException("Index: "+index);
}
// Preserves singleton property
private Object readResolve() {
return EMPTY_LIST;
}
}
/**
* The empty map (immutable). This map is serializable.
*
* @since 1.3
*/
public static final Map EMPTY_MAP = new EmptyMap();
private static class EmptyMap extends AbstractMap implements Serializable {
private static final long serialVersionUID = 6428348081105594320L;
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean containsKey(Object key) {return false;}
public boolean containsValue(Object value) {return false;}
public Object get(Object key) {return null;}
public Set keySet() {return EMPTY_SET;}
public Collection values() {return EMPTY_SET;}
public Set entrySet() {return EMPTY_SET;}
public boolean equals(Object o) {
return (o instanceof Map) && ((Map)o).size()==0;
}
public int hashCode() {return 0;}
// Preserves singleton property
private Object readResolve() {
return EMPTY_MAP;
}
}
/**
* Returns an immutable set containing only the specified object.
* The returned set is serializable.
*
* @param o the sole object to be stored in the returned set.
* @return an immutable set containing only the specified object.
*/
public static Set singleton(Object o) {
return new SingletonSet(o);
}
/**
* @serial include
*/
private static class SingletonSet extends AbstractSet
implements Serializable
{
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 3193687207550431679L;
private Object element;
SingletonSet(Object o) {element = o;}
public Iterator iterator() {
return new Iterator() {
private boolean hasNext = true;
public boolean hasNext() {
return hasNext;
}
public Object next() {
if (hasNext) {
hasNext = false;
return element;
}
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public int size() {return 1;}
public boolean contains(Object o) {return eq(o, element);}
}
/**
* Returns an immutable list containing only the specified object.
* The returned list is serializable.
*
* @param o the sole object to be stored in the returned list.
* @return an immutable list containing only the specified object.
* @since 1.3
*/
public static List singletonList(Object o) {
return new SingletonList(o);
}
private static class SingletonList extends AbstractList
implements RandomAccess, Serializable {
static final long serialVersionUID = 3093736618740652951L;
private final Object element;
SingletonList(Object obj) {element = obj;}
public int size() {return 1;}
public boolean contains(Object obj) {return eq(obj, element);}
public Object get(int index) {
if (index != 0)
throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
return element;
}
}
/**
* Returns an immutable map, mapping only the specified key to the
* specified value. The returned map is serializable.
*
* @param key the sole key to be stored in the returned map.
* @param value the value to which the returned map maps <tt>key</tt>.
* @return an immutable map containing only the specified key-value
* mapping.
* @since 1.3
*/
public static Map singletonMap(Object key, Object value) {
return new SingletonMap(key, value);
}
private static class SingletonMap extends AbstractMap
implements Serializable {
private final Object k, v;
SingletonMap(Object key, Object value) {
k = key;
v = value;
}
public int size() {return 1;}
public boolean isEmpty() {return false;}
public boolean containsKey(Object key) {return eq(key, k);}
public boolean containsValue(Object value) {return eq(value, v);}
public Object get(Object key) {return (eq(key, k) ? v : null);}
private transient Set keySet = null;
private transient Set entrySet = null;
private transient Collection values = null;
public Set keySet() {
if (keySet==null)
keySet = singleton(k);
return keySet;
}
public Set entrySet() {
if (entrySet==null)
entrySet = singleton(new ImmutableEntry(k, v));
return entrySet;
}
public Collection values() {
if (values==null)
values = singleton(v);
return values;
}
private static class ImmutableEntry implements Map.Entry {
final Object k;
final Object v;
ImmutableEntry(Object key, Object value) {
k = key;
v = value;
}
public Object getKey() {return k;}
public Object getValue() {return v;}
public Object setValue(Object value) {
throw new UnsupportedOperationException();
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
return eq(e.getKey(), k) && eq(e.getValue(), v);
}
public int hashCode() {
return ((k==null ? 0 : k.hashCode()) ^
(v==null ? 0 : v.hashCode()));
}
public String toString() {
return k+"="+v;
}
}
}
/**
* Returns an immutable list consisting of <tt>n</tt> copies of the
* specified object. The newly allocated data object is tiny (it contains
* a single reference to the data object). This method is useful in
* combination with the <tt>List.addAll</tt> method to grow lists.
* The returned list is serializable.
*
* @param n the number of elements in the returned list.
* @param o the element to appear repeatedly in the returned list.
* @return an immutable list consisting of <tt>n</tt> copies of the
* specified object.
* @throws IllegalArgumentException if n < 0.
* @see List#addAll(Collection)
* @see List#addAll(int, Collection)
*/
public static List nCopies(int n, Object o) {
return new CopiesList(n, o);
}
/**
* @serial include
*/
private static class CopiesList extends AbstractList
implements RandomAccess, Serializable
{
static final long serialVersionUID = 2739099268398711800L;
int n;
Object element;
CopiesList(int n, Object o) {
if (n < 0)
throw new IllegalArgumentException("List length = " + n);
this.n = n;
element = o;
}
public int size() {
return n;
}
public boolean contains(Object obj) {
return n != 0 && eq(obj, element);
}
public Object get(int index) {
if (index<0 || index>=n)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+n);
return element;
}
}
/**
* Returns a comparator that imposes the reverse of the <i>natural
* ordering</i> on a collection of objects that implement the
* <tt>Comparable</tt> interface. (The natural ordering is the ordering
* imposed by the objects' own <tt>compareTo</tt> method.) This enables a
* simple idiom for sorting (or maintaining) collections (or arrays) of
* objects that implement the <tt>Comparable</tt> interface in
* reverse-natural-order. For example, suppose a is an array of
* strings. Then: <pre>
* Arrays.sort(a, Collections.reverseOrder());
* </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
*
* The returned comparator is serializable.
*
* @return a comparator that imposes the reverse of the <i>natural
* ordering</i> on a collection of objects that implement
* the <tt>Comparable</tt> interface.
* @see Comparable
*/
public static Comparator reverseOrder() {
return REVERSE_ORDER;
}
private static final Comparator REVERSE_ORDER = new ReverseComparator();
/**
* @serial include
*/
private static class ReverseComparator implements Comparator,Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 7207038068494060240L;
public int compare(Object o1, Object o2) {
Comparable c1 = (Comparable)o1;
Comparable c2 = (Comparable)o2;
int cmp = c1.compareTo(c2);
/*
* We can't simply return -cmp, as -Integer.MIN_VALUE ==
* Integer.MIN_VALUE.
*/
return -(cmp | (cmp >>> 1));
}
}
/**
* Returns an enumeration over the specified collection. This provides
* interoperatbility with legacy APIs that require an enumeration
* as input.
*
* @param c the collection for which an enumeration is to be returned.
* @return an enumeration over the specified collection.
* @see Enumeration
*/
public static Enumeration enumeration(final Collection c) {
return new Enumeration() {
Iterator i = c.iterator();
public boolean hasMoreElements() {
return i.hasNext();
}
public Object nextElement() {
return i.next();
}
};
}
/**
* Returns an array list containing the elements returned by the
* specified enumeration in the order they are returned by the
* enumeration. This method provides interoperatbility between
* legacy APIs that return enumerations and new APIs that require
* collections.
*
* @param e enumeration providing elements for the returned
* array list
* @return an array list containing the elements returned
* by the specified enumeration.
* @since 1.4
* @see Enumeration
* @see ArrayList
*/
public static ArrayList list(Enumeration e) {
ArrayList l = new ArrayList();
while (e.hasMoreElements())
l.add(e.nextElement());
return l;
}
/**
* Returns true if the specified arguments are equal, or both null.
*/
private static boolean eq(Object o1, Object o2) {
return (o1==null ? o2==null : o1.equals(o2));
}
}