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java.lang.Objectrailo.commons.collections.Collections
public final class Collections
Field Summary | |
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static List |
EMPTY_LIST
The empty list (immutable). |
static Map |
EMPTY_MAP
The empty map (immutable). |
static Set |
EMPTY_SET
The empty set (immutable). |
Method Summary | |
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static int |
binarySearch(List list,
Object key)
|
static int |
binarySearch(List list,
Object key,
Comparator c)
|
static void |
copy(List dest,
List src)
Copies all of the elements from one list into another. |
static Enumeration |
enumeration(Collection c)
|
static void |
fill(List list,
Object obj)
Replaces all of the elements of the specified list with the specified element. |
static int |
indexOfSubList(List source,
List target)
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. |
static int |
lastIndexOfSubList(List source,
List 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. |
static ArrayList |
list(Enumeration e)
|
static Object |
max(Collection coll)
|
static Object |
max(Collection coll,
Comparator comp)
|
static Object |
min(Collection coll)
|
static Object |
min(Collection coll,
Comparator comp)
|
static List |
nCopies(int n,
Object o)
|
static boolean |
replaceAll(List list,
Object oldVal,
Object newVal)
Replaces all occurrences of one specified value in a list with another. |
static void |
reverse(List list)
Reverses the order of the elements in the specified list. |
static Comparator |
reverseOrder()
|
static void |
rotate(List list,
int distance)
Rotates the elements in the specified list by the specified distance. |
static void |
shuffle(List list)
Randomly permutes the specified list using a default source of randomness. |
static void |
shuffle(List list,
Random rnd)
Randomly permute the specified list using the specified source of randomness. |
static Set |
singleton(Object o)
Returns an immutable set containing only the specified object. |
static List |
singletonList(Object o)
Returns an immutable list containing only the specified object. |
static Map |
singletonMap(Object key,
Object value)
Returns an immutable map, mapping only the specified key to the specified value. |
static void |
sort(List list)
|
static void |
sort(List list,
Comparator c)
|
static void |
swap(List list,
int i,
int j)
Swaps the elements at the specified positions in the specified list. |
static Collection |
synchronizedCollection(Collection c)
Returns a synchronized (thread-safe) collection backed by the specified collection. |
static List |
synchronizedList(List list)
Returns a synchronized (thread-safe) list backed by the specified list. |
static Map |
synchronizedMap(Map m)
Returns a synchronized (thread-safe) map backed by the specified map. |
static Set |
synchronizedSet(Set s)
Returns a synchronized (thread-safe) set backed by the specified set. |
static SortedMap |
synchronizedSortedMap(SortedMap m)
Returns a synchronized (thread-safe) sorted map backed by the specified sorted map. |
static SortedSet |
synchronizedSortedSet(SortedSet s)
Returns a synchronized (thread-safe) sorted set backed by the specified sorted set. |
static Collection |
unmodifiableCollection(Collection c)
Returns an unmodifiable view of the specified collection. |
static List |
unmodifiableList(List list)
Returns an unmodifiable view of the specified list. |
static Map |
unmodifiableMap(Map m)
Returns an unmodifiable view of the specified map. |
static Set |
unmodifiableSet(Set s)
Returns an unmodifiable view of the specified set. |
static SortedMap |
unmodifiableSortedMap(SortedMap m)
Returns an unmodifiable view of the specified sorted map. |
static SortedSet |
unmodifiableSortedSet(SortedSet s)
Returns an unmodifiable view of the specified sorted set. |
Methods inherited from class java.lang.Object |
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equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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public static final Set EMPTY_SET
public static final List EMPTY_LIST
public static final Map EMPTY_MAP
Method Detail |
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public static void sort(List list)
public static void sort(List list, Comparator c)
public static int binarySearch(List list, Object key)
public static int binarySearch(List list, Object key, Comparator c)
public static void reverse(List list)
This method runs in linear time.
list
- the list whose elements are to be reversed.
UnsupportedOperationException
- if the specified list or
its list-iterator does not support the set method.public static void shuffle(List list)
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.
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.
This method runs in linear time. If the specified list does not
implement the 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.
list
- the list to be shuffled.
UnsupportedOperationException
- if the specified list or
its list-iterator does not support the set method.public static void shuffle(List list, Random rnd)
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.
This method runs in linear time. If the specified list does not
implement the 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.
list
- the list to be shuffled.rnd
- the source of randomness to use to shuffle the list.
UnsupportedOperationException
- if the specified list or its
list-iterator does not support the set operation.public static void swap(List list, int i, int j)
list
- The list in which to swap elements.i
- the index of one element to be swapped.j
- the index of the other element to be swapped.
IndexOutOfBoundsException
- if either i or j
is out of range (i < 0 || i >= list.size()
|| j < 0 || j >= list.size()).public static void fill(List list, Object obj)
This method runs in linear time.
list
- the list to be filled with the specified element.obj
- The element with which to fill the specified list.
UnsupportedOperationException
- if the specified list or its
list-iterator does not support the set operation.public static void copy(List dest, List src)
This method runs in linear time.
dest
- The destination list.src
- The source list.
IndexOutOfBoundsException
- if the destination list is too small
to contain the entire source List.
UnsupportedOperationException
- if the destination list's
list-iterator does not support the set operation.public static Object min(Collection coll)
public static Object min(Collection coll, Comparator comp)
public static Object max(Collection coll)
public static Object max(Collection coll, Comparator comp)
public static void rotate(List list, int distance)
For example, suppose list comprises [t, a, n, k, s]. After invoking Collections.rotate(list, 1) (or Collections.rotate(list, -4)), list will comprise [s, t, a, n, k].
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 j forward to position k (which must be greater than or equal to j):
Collections.rotate(list.subList(j, k+1), -1);To make this concrete, suppose list comprises [a, b, c, d, e]. To move the element at index 1 (b) forward two positions, perform the following invocation:
Collections.rotate(l.subList(1, 4), -1);The resulting list is [a, c, d, b, e].
To move more than one element forward, increase the absolute value of the rotation distance. To move elements backward, use a positive shift distance.
If the specified list is small or implements the 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
RandomAccess interface, this implementation breaks the
list into two sublist views around index -distance mod size.
Then the 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
Programming Pearls (Addison-Wesley, 1986).
list
- the list to be rotated.distance
- the distance to rotate the list. There are no
constraints on this value; it may be zero, negative, or
greater than list.size().
UnsupportedOperationException
- if the specified list or
its list-iterator does not support the set method.public static boolean replaceAll(List list, Object oldVal, Object newVal)
list
- the list in which replacement is to occur.oldVal
- the old value to be replaced.newVal
- the new value with which oldVal is to be
replaced.
UnsupportedOperationException
- if the specified list or
its list-iterator does not support the set method.public static int indexOfSubList(List source, List target)
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.
source
- the list in which to search for the first occurrence
of target.target
- the list to search for as a subList of source.
public static int lastIndexOfSubList(List source, List target)
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.
source
- the list in which to search for the last occurrence
of target.target
- the list to search for as a subList of source.
public static Collection unmodifiableCollection(Collection c)
The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object'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.
The returned collection will be serializable if the specified collection is serializable.
c
- the collection for which an unmodifiable view is to be
returned.
public static Set unmodifiableSet(Set s)
The returned set will be serializable if the specified set is serializable.
s
- the set for which an unmodifiable view is to be returned.
public static SortedSet unmodifiableSortedSet(SortedSet s)
The returned sorted set will be serializable if the specified sorted set is serializable.
s
- the sorted set for which an unmodifiable view is to be
returned.
public static List unmodifiableList(List list)
The returned list will be serializable if the specified list
is serializable. Similarly, the returned list will implement
RandomAccess
if the specified list does.
the
list
- the list for which an unmodifiable view is to be returned.
public static Map unmodifiableMap(Map m)
The returned map will be serializable if the specified map is serializable.
m
- the map for which an unmodifiable view is to be returned.
public static SortedMap unmodifiableSortedMap(SortedMap m)
The returned sorted map will be serializable if the specified sorted map is serializable.
m
- the sorted map for which an unmodifiable view is to be
returned.
public static Collection synchronizedCollection(Collection c)
It is imperative that the user manually synchronize on the returned collection when iterating over it:
Collection c = Collections.synchronizedCollection(myCollection); ... synchronized(c) { Iterator i = c.iterator(); // Must be in the synchronized block while (i.hasNext()) foo(i.next()); }Failure to follow this advice may result in non-deterministic behavior.
The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object'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.
The returned collection will be serializable if the specified collection is serializable.
c
- the collection to be "wrapped" in a synchronized collection.
public static Set synchronizedSet(Set s)
It is imperative that the user manually synchronize on the returned set when iterating over it:
Set s = Collections.synchronizedSet(new HashSet()); ... synchronized(s) { Iterator i = s.iterator(); // Must be in the synchronized block while (i.hasNext()) foo(i.next()); }Failure to follow this advice may result in non-deterministic behavior.
The returned set will be serializable if the specified set is serializable.
s
- the set to be "wrapped" in a synchronized set.
public static SortedSet synchronizedSortedSet(SortedSet s)
It is imperative that the user manually synchronize on the returned sorted set when iterating over it or any of its subSet, headSet, or tailSet views.
SortedSet s = Collections.synchronizedSortedSet(new HashSortedSet()); ... synchronized(s) { Iterator i = s.iterator(); // Must be in the synchronized block while (i.hasNext()) foo(i.next()); }or:
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()); }Failure to follow this advice may result in non-deterministic behavior.
The returned sorted set will be serializable if the specified sorted set is serializable.
s
- the sorted set to be "wrapped" in a synchronized sorted set.
public static List synchronizedList(List list)
It is imperative that the user manually synchronize on the returned list when iterating over it:
List list = Collections.synchronizedList(new ArrayList()); ... synchronized(list) { Iterator i = list.iterator(); // Must be in synchronized block while (i.hasNext()) foo(i.next()); }Failure to follow this advice may result in non-deterministic behavior.
The returned list will be serializable if the specified list is serializable.
list
- the list to be "wrapped" in a synchronized list.
public static Map synchronizedMap(Map m)
It is imperative that the user manually synchronize on the returned map when iterating over any of its collection views:
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()); }Failure to follow this advice may result in non-deterministic behavior.
The returned map will be serializable if the specified map is serializable.
m
- the map to be "wrapped" in a synchronized map.
public static SortedMap synchronizedSortedMap(SortedMap m)
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 subMap, headMap or tailMap views.
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()); }or:
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()); }Failure to follow this advice may result in non-deterministic behavior.
The returned sorted map will be serializable if the specified sorted map is serializable.
m
- the sorted map to be "wrapped" in a synchronized sorted map.
public static Set singleton(Object o)
o
- the sole object to be stored in the returned set.
public static List singletonList(Object o)
o
- the sole object to be stored in the returned list.
public static Map singletonMap(Object key, Object value)
key
- the sole key to be stored in the returned map.value
- the value to which the returned map maps key.
public static List nCopies(int n, Object o)
public static Comparator reverseOrder()
public static Enumeration enumeration(Collection c)
public static ArrayList list(Enumeration e)
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