public class java.util.Collections

ReverseComparator

SubList<A>

SubList - Implements a SubList view backed by an arbitrary List.

SynchronizedCollection<A>

SynchronizedList<A>

SynchronizedMap<A, B>

SynchronizedSet<A>

SynchronizedSortedMap<A, B>

SynchronizedSortedSet<A>

UnmodifiableCollection<A>

UnmodifiableList<A>

UnmodifiableMap<A, B>

UnmodifiableSet<A>

UnmodifiableSortedMap<A, B>

UnmodifiableSortedSet<A>

public Collections();

public static final Comparator<A> REVERSE_ORDER;

A Comparator that imposes the reverse of the natural ordering on a collection of Comparable objects. (The natural ordering is the ordering imposed by the objects' own compareTo method.) This enables a simple idiom for sorting (or maintaining) collections (or arrays) of Comparable objects in reverse-natural-order. For example, suppose a is an array of String. Then:

 		Arrays.sort(a, Collections.REVERSE_ORDER);
 

sorts the array in reverse-lexicographic (alphabetical) order.

This Comparator is Serializable.

public static <A> void sort(List<A> list);

Sorts the specified List into ascending order, according to the natural comparison method of its elements. All elements in the List must implement the Comparable interface. Furthermore, all elements in the List must be mutually comparable (that is, e1.compareTo(e2) must not throw a typeMismatchException for any elements e1 and e2 in the List).

The sorting algorithm is a tuned quicksort, adapted from Jon L. Bentley and M. Douglas McIlroy's "Engineering a Sort Function", Software-Practice and Experience, Vol. 23(11) P. 1249-1265 (November 1993). This algorithm offers n*log(n) performance on many data sets that cause other quicksorts to degrade to quadratic performance.

The specified List must be modifiable, but need not be resizable. This implementation dumps the specified List into an List, sorts the array, and iterates over the List resetting each element from the corresponding position in the array. This avoids the n^2*log(n) performance that would result from attempting to sort a LinkedList in place.

Parameters:

list - the List to be sorted.

Throws:

ClassCastException -List contains elements that are not mutually comparable (for example, Strings and Integers).

UnsupportedOperationException -The specified List's ListIterator not support the set operation.

See also:

Comparable

sort

public static <A> void sort(List<A> list,
                            Comparator<A> c);

Sorts the specified List according to the order induced by the specified Comparator. All elements in the List must be mutually comparable by the specified comparator (that is, comparator.compare(e1, e2) must not throw a typeMismatchException for any elements e1 and e2 in the List).

The sorting algorithm is a tuned quicksort, adapted from Jon L. Bentley and M. Douglas McIlroy's "Engineering a Sort Function", Software-Practice and Experience, Vol. 23(11) P. 1249-1265 (November 1993). This algorithm offers n*log(n) performance on many data sets that cause other quicksorts to degrade to quadratic performance.

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^2*log(n) performance that would result from attempting to sort a LinkedList in place.

Parameters:

list - the List to be sorted.

Throws:

ClassCastException -List contains elements that are not mutually comparable with the specified Comparator.

UnsupportedOperationException -The specified List's did ListIterator not support the set operation.

See also:

Comparator

binarySearch

public static <A> int binarySearch(List<A> list,
                                   A key);

Searches the specified List for the specified Object using the binary search algorithm. The List must be sorted into ascending order according to the natural comparison method of its elements (as by Sort(List), above) prior to making this call. If it is not sorted, the results are undefined: in particular, the call may enter an infinite loop. If the List contains multiple elements equal to the specified Object, there is no guarantee which instance will be found.

This method will run in log(n) time for a "random access" List (which provides near-constant-time positional access) like a Vector. It may run in n*log(n) time if it is called on a "sequential access" List (which provides linear-time positional access). If the specified List is an instanceof AbstracSequentialList, this method will do a sequential search instead of a binary search; this offers linear performance instead of n*log(n) performance if this method is called on a LinkedList.

Parameters:

list - the List to be searched.

key - the key to be searched for.

Returns:

index of the search key, if it is contained in the List; otherwise, (-(insertion point) - 1). The insertion point is defined as the the point at which the value would be inserted into the List: the index of the first element greater than the value, or list.size(), if all elements in the List are less than the specified value. Note that this guarantees that the return value will be >= 0 if and only if the Object is found.

Throws:

ClassCastException -List contains elements that are not mutually comparable (for example, Strings and Integers), or the search key in not mutually comparable with the elements of the List.

See also:

Comparable, sort(List)

binarySearch

public static <A> int binarySearch(List<A> list,
                                   A key,
                                   Comparator<A> c);

Searches the specified List for the specified Object using the binary search algorithm. The List must be sorted into ascending order according to the specified Comparator (as by Sort(List, Comparator), above), prior to making this call.

This method will run in log(n) time for a "random access" List (which provides near-constant-time positional access) like a Vector. It may run in n*log(n) time if it is called on a "sequential access" List (which provides linear-time positional access). If the specified List is an instanceof AbstracSequentialList, this method will do a sequential search instead of a binary search; this offers linear performance instead of n*log(n) performance if this method is called on a LinkedList.

Parameters:

list - the List to be searched.

key - the key to be searched for.

Returns:

index of the search key, if it is contained in the List; otherwise, (-(insertion point) - 1). The insertion point is defined as the the point at which the value would be inserted into the List: the index of the first element greater than the value, or list.size(), if all elements in the List are less than the specified value. Note that this guarantees that the return value will be >= 0 if and only if the Object is found.

Throws:

ClassCastException -List contains elements that are not mutually comparable with the specified Comparator, or the search key in not mutually comparable with the elements of the List using this Comparator.

See also:

Comparable, sort(List, Comparator)

min

public static <A> A min(Collection<A> coll);

Returns the minimum element of the given Collection, according to the natural comparison method of its elements. All elements in the Collection must implement the Comparable interface. Furthermore, all elements in the Collection must be mutually comparable (that is, e1.compareTo(e2) must not throw a typeMismatchException for any elements e1 and e2 in the Collection).

This method iterates over the entire Collection, hence it requires time proportional to the size of the Collection.

Parameters:

coll - the collection whose minimum element is to be determined.

Throws:

ClassCastException -Collection contains elements that are not mutually comparable (for example, Strings and Integers).

NoSuchElementException -Collection is empty.

See also:

Comparable

min

public static <A> A min(Collection<A> coll,
                        Comparator<A> comp);

Returns the minimum element of the given Collection, according to the order induced by the specified Comparator. All elements in the Collection must be mutually comparable by the specified comparator (that is, comparator.compare(e1, e2) must not throw a typeMismatchException for any elements e1 and e2 in the Collection).

This method iterates over the entire Collection, hence it requires time proportional to the size of the Collection.

Parameters:

coll - the collection whose minimum element is to be determined.

Throws:

ClassCastException -Collection contains elements that are not mutually comparable with the specified Comparator.

NoSuchElementException -Collection is empty.

See also:

Comparable

max

public static <A> A max(Collection<A> coll);

Returns the maximum element of the given Collection, according to the natural comparison method of its elements. All elements in the Collection must implement the Comparable interface. Furthermore, all elements in the Collection must be mutually comparable (that is, e1.compareTo(e2) must not throw a typeMismatchException for any elements e1 and e2 in the Collection).

This method iterates over the entire Collection, hence it requires time proportional to the size of the Collection.

Parameters:

coll - the collection whose maximum element is to be determined.

Throws:

ClassCastException -Collection contains elements that are not mutually comparable (for example, Strings and Integers).

NoSuchElementException -Collection is empty.

See also:

Comparable

max

public static <A> A max(Collection<A> coll,
                        Comparator<A> comp);

Returns the maximum element of the given Collection, according to the order induced by the specified Comparator. All elements in the Collection must be mutually comparable by the specified comparator (that is, comparator.compare(e1, e2) must not throw a typeMismatchException for any elements e1 and e2 in the Collection).

This method iterates over the entire Collection, hence it requires time proportional to the size of the Collection.

Parameters:

coll - the collection whose maximum element is to be determined.

Throws:

ClassCastException -Collection contains elements that are not mutually comparable with the specified Comparator.

NoSuchElementException -Collection is empty.

See also:

Comparable

subList

public static <A> List<A> subList(List<A> list,
                                  int fromIndex,
                                  int toIndex);

Returns a List backed by the specified List that represents the portion of the specified List whose index ranges from fromIndex (inclusive) to toIndex (exclusive). The returned List is not resizable. (Its size is fixed at (toIndex - fromIndex).) The returned List is mutable iff the specified List is mutable. Changes to the returned List "write through" to the specified List, and vice-versa.

If the caller wants a List that is independent of the input List, and free of the restrictions noted above, he should immediately copy the returned List into a new List, for example:

     Vector v = new Vector(Collections.subList(myList, 17, 42));
 

Parameters:

list - the List whose subList is to be returned.

fromIndex - the index (in this List) of the first element to appear in the subList.

toIndex - the index (in this List) following the last element to appear in the subList.

Throws:

IndexOutOfBoundsException -fromIndex or toIndex is out of range (fromIndex < 0 || fromIndex > size || toIndex < 0 || toIndex > size).

IllegalArgumentException -fromIndex > toIndex.

unmodifiableCollection

public static <A> Collection<A> unmodifiableCollection(Collection<A> c);

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 UnsupportedOperationException.

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.

Parameters:

c - the Collection for which an unmodifiable view is to be returned.

unmodifiableSet

public static <A> Set<A> unmodifiableSet(Set<A> s);

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 UnsupportedOperationException.

The returned Set will be Serializable if the specified Set is Serializable.

Parameters:

s - the Set for which an unmodifiable view is to be returned.

unmodifiableSortedSet

public static <A> SortedSet<A> unmodifiableSortedSet(SortedSet<A> s);

Returns an unmodifiable view of the specified SortedSet. This method allows modules to provide users with "read-only" access to internal SortedSets. Query operations on the returned SortedSet "read through" to the specified SortedSet. Attempts to modify the returned SortedSet, whether direct, via its Iterator, or via its subSet, headSet, or tailSet views, result in an UnsupportedOperationException.

The returned SortedSet will be Serializable if the specified SortedSet is Serializable.

Parameters:

s - the SortedSet for which an unmodifiable view is to be returned.

unmodifiableList

public static <A> List<A> unmodifiableList(List<A> list);

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 UnsupportedOperationException.

The returned List will be Serializable if the specified List is Serializable.

Parameters:

list - the List for which an unmodifiable view is to be returned.

unmodifiableMap

public static <A, B> Map<A, B> unmodifiableMap(Map<A, B> m);

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 UnsupportedOperationException.

The returned Map will be Serializable if the specified Map is Serializable.

Parameters:

m - the Map for which an unmodifiable view is to be returned.

unmodifiableSortedMap

public static <A, B> SortedMap<A, B> unmodifiableSortedMap(SortedMap<A, B> m);

Returns an unmodifiable view of the specified SortedMap. This method allows modules to provide users with "read-only" access to internal SortedMaps. Query operations on the returned SortedMap "read through" to the specified SortedMap. Attempts to modify the returned SortedMap, whether direct, via its Collection views, or via its subMap, headMap, or tailMap views, result in an UnsupportedOperationException.

The returned SortedMap will be Serializable if the specified SortedMap is Serializable.

Parameters:

m - the SortedMap for which an unmodifiable view is to be returned.

synchronizedCollection

public static <A> Collection<A> synchronizedCollection(Collection<A> c);

Returns a synchronized (thread-safe) Collection backed by the specified Collection. In order to guarantee serial access, it is critical that all access to the backing Collection is accomplished through the returned Collection.

It is imperative that the user manually synchronize on the returned Collection when iterating over it:

  Collection c = 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.

Parameters:

c - the Collection to be "wrapped" in a synchronized Collection.

synchronizedSet

public static <A> Set<A> synchronizedSet(Set<A> s);

Returns a synchronized (thread-safe) Set backed by the specified Set. In order to guarantee serial access, it is critical that all access to the backing Set is accomplished through the returned Set.

It is imperative that the user manually synchronize on the returned Set when iterating over it:

  Set s = 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.

Parameters:

s - the Set to be "wrapped" in a synchronized Set.

synchronizedSortedSet

public static <A> SortedSet<A> synchronizedSortedSet(SortedSet<A> s);

Returns a synchronized (thread-safe) SortedSet backed by the specified SortedSet. In order to guarantee serial access, it is critical that all access to the backing SortedSet is accomplished through the returned SortedSet (or its views).

It is imperative that the user manually synchronize on the returned SortedSet when iterating over it or any of its subSet, headSet, or tailSet views.

  SortedSet s = synchronizedSortedSet(new HashSortedSet());
      ...
  synchronized(s) {
      Iterator i = s.iterator(); // Must be in the synchronized block
      while (i.hasNext())
          foo(i.next();
  }
 

or:

  SortedSet s = 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 SortedSet will be Serializable if the specified SortedSet is Serializable.

Parameters:

s - the SortedSet to be "wrapped" in a synchronized SortedSet.

synchronizedList

public static <A> List<A> synchronizedList(List<A> list);

Returns a synchronized (thread-safe) List backed by the specified List. In order to guarantee serial access, it is critical that all access to the backing List is accomplished through the returned List.

It is imperative that the user manually synchronize on the returned List when iterating over it:

  List list = 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.

Parameters:

list - the List to be "wrapped" in a synchronized List.

synchronizedMap

public static <A, B> Map<A, B> synchronizedMap(Map<A, B> m);

Returns a synchronized (thread-safe) Map backed by the specified Map. In order to guarantee serial access, it is critical that all access to the backing Map is accomplished through the returned Map.

It is imperative that the user manually synchronize on the returned Map when iterating over any of its Collection views:

  Map m = 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.

Parameters:

m - the Map to be "wrapped" in a synchronized Map.

synchronizedSortedMap

public static <A, B> SortedMap<A, B> synchronizedSortedMap(SortedMap<A, B> m);

Returns a synchronized (thread-safe) SortedMap backed by the specified SortedMap. In order to guarantee serial access, it is critical that all access to the backing SortedMap is accomplished through the returned SortedMap (or its views).

It is imperative that the user manually synchronize on the returned SortedMap when iterating over any of its Collection views, or the Collections views of any of its subMap, headMap or tailMap views.

  SortedMap m = 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 = 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 SortedMap will be Serializable if the specified SortedMap is Serializable.

Parameters:

m - the SortedMap to be "wrapped" in a synchronized SortedMap.

nCopies

public static <A> List<A> nCopies(int n,
                                  A o);

Returns an immutable List consisting of n 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 List.addAll to grow Lists.

Parameters:

n - the number of elements in the returned List.

o - the element to appear repeatedly in the returned List.

Throws:

IllegalArgumentException -n < 0.

See also:

addAll(Collection), addAll(int, Collection)

enumeration

public static Enumeration enumeration(Collection<A> c);

Returns an Enumeration over the specified Collection. This provides interoperatbility with legacy APIs that require an Enumeration as input.

Parameters:

c - the Collection for which an Enumeration is to be returned.

static class SubList<A>
  extends AbstractList<A>

SubList - Implements a SubList view backed by an arbitrary List.

static class UnmodifiableCollection<A>

static class UnmodifiableCollection<A>
  implements Collection<A>, Serializable

static class UnmodifiableSet<A>

static class UnmodifiableSet<A>
  extends UnmodifiableCollection<A>
  implements Set<A>, Serializable

static class UnmodifiableSortedSet<A>

static class UnmodifiableSortedSet<A>
  extends UnmodifiableSet<A>
  implements SortedSet<A>, Serializable

static class UnmodifiableList<A>

static class UnmodifiableList<A>
  extends UnmodifiableCollection<A>
  implements List<A>

private static class UnmodifiableMap<A, B>

private static class UnmodifiableMap<A, B>
  implements Map<A, B>, Serializable

static class UnmodifiableSortedMap<A, B>

static class UnmodifiableSortedMap<A, B>
  extends UnmodifiableMap<A, B>
  implements SortedMap<A, B>, Serializable

static class SynchronizedCollection<A>

static class SynchronizedCollection<A>
  implements Collection<A>, Serializable

static class SynchronizedSet<A>

static class SynchronizedSet<A>
  extends SynchronizedCollection<A>
  implements Set<A>

static class SynchronizedSortedSet<A>

static class SynchronizedSortedSet<A>
  extends SynchronizedSet<A>
  implements SortedSet<A>

static class SynchronizedList<A>

static class SynchronizedList<A>
  extends SynchronizedCollection<A>
  implements List<A>

private static class SynchronizedMap<A, B>

private static class SynchronizedMap<A, B>
  implements Map<A, B>

static class SynchronizedSortedMap<A, B>

static class SynchronizedSortedMap<A, B>
  extends SynchronizedMap<A, B>
  implements SortedMap<A, B>

private static class ReverseComparator

private static class ReverseComparator
  implements Comparator<A>, Serializable

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