railo.commons.collections
Class Collections

java.lang.Object
  extended by railo.commons.collections.Collections

public final class Collections
extends Object


Field Summary
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
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
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

EMPTY_SET

public static final Set EMPTY_SET
The empty set (immutable). This set is serializable.


EMPTY_LIST

public static final List EMPTY_LIST
The empty list (immutable). This list is serializable.


EMPTY_MAP

public static final Map EMPTY_MAP
The empty map (immutable). This map is serializable.

Method Detail

sort

public static void sort(List list)

sort

public static void sort(List list,
                        Comparator c)

binarySearch

public static int binarySearch(List list,
                               Object key)

binarySearch

public static int binarySearch(List list,
                               Object key,
                               Comparator c)

reverse

public static void reverse(List list)
Reverses the order of the elements in the specified list.

This method runs in linear time.

Parameters:
list - the list whose elements are to be reversed.
Throws:
UnsupportedOperationException - if the specified list or its list-iterator does not support the set method.

shuffle

public static void shuffle(List list)
Randomly permutes the specified list using a default source of randomness. All permutations occur with approximately equal likelihood.

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.

Parameters:
list - the list to be shuffled.
Throws:
UnsupportedOperationException - if the specified list or its list-iterator does not support the set method.

shuffle

public static void shuffle(List list,
                           Random rnd)
Randomly permute the specified list using the specified source of randomness. All permutations occur with equal likelihood assuming that the source of randomness is fair.

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.

Parameters:
list - the list to be shuffled.
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 set operation.

swap

public static void swap(List list,
                        int i,
                        int j)
Swaps the elements at the specified positions in the specified list. (If the specified positions are equal, invoking this method leaves the list unchanged.)

Parameters:
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.
Throws:
IndexOutOfBoundsException - if either i or j is out of range (i < 0 || i >= list.size() || j < 0 || j >= list.size()).

fill

public static void fill(List list,
                        Object obj)
Replaces all of the elements of the specified list with the specified element.

This method runs in linear time.

Parameters:
list - the list to be filled with the specified element.
obj - The element with which to fill the specified list.
Throws:
UnsupportedOperationException - if the specified list or its list-iterator does not support the set operation.

copy

public static void copy(List dest,
                        List src)
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.

This method runs in linear time.

Parameters:
dest - The destination list.
src - The source list.
Throws:
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.

min

public static Object min(Collection coll)

min

public static Object min(Collection coll,
                         Comparator comp)

max

public static Object max(Collection coll)

max

public static Object max(Collection coll,
                         Comparator comp)

rotate

public static void rotate(List list,
                          int distance)
Rotates the elements in the specified list by the specified distance. After calling this method, the element at index i will be the element previously at index (i - distance) mod list.size(), for all values of i between 0 and list.size()-1, inclusive. (This method has no effect on the size of the list.)

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).

Parameters:
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().
Throws:
UnsupportedOperationException - if the specified list or its list-iterator does not support the set method.

replaceAll

public static boolean replaceAll(List list,
                                 Object oldVal,
                                 Object newVal)
Replaces all occurrences of one specified value in a list with another. More formally, replaces with newVal each element e in list such that (oldVal==null ? e==null : oldVal.equals(e)). (This method has no effect on the size of the list.)

Parameters:
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.
Returns:
true if list contained one or more elements e such that (oldVal==null ? e==null : oldVal.equals(e)).
Throws:
UnsupportedOperationException - if the specified list or its list-iterator does not support the set method.

indexOfSubList

public 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. More formally, returns the the lowest index i such that source.subList(i, i+target.size()).equals(target), or -1 if there is no such index. (Returns -1 if target.size() > source.size().)

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.

Parameters:
source - the list in which to search for the first occurrence of target.
target - the list to search for as a subList of source.
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.

lastIndexOfSubList

public 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. More formally, returns the the highest index i such that source.subList(i, i+target.size()).equals(target), or -1 if there is no such index. (Returns -1 if target.size() > source.size().)

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.

Parameters:
source - the list in which to search for the last occurrence of target.
target - the list to search for as a subList of source.
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.

unmodifiableCollection

public static Collection unmodifiableCollection(Collection 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.
Returns:
an unmodifiable view of the specified collection.

unmodifiableSet

public static Set unmodifiableSet(Set 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.
Returns:
an unmodifiable view of the specified set.

unmodifiableSortedSet

public static SortedSet unmodifiableSortedSet(SortedSet s)
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 subSet, headSet, or tailSet views, result in an UnsupportedOperationException.

The returned sorted set will be serializable if the specified sorted set is serializable.

Parameters:
s - the sorted set for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified sorted set.

unmodifiableList

public static List unmodifiableList(List 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. Similarly, the returned list will implement RandomAccess if the specified list does. the

Parameters:
list - the list for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified list.

unmodifiableMap

public static Map unmodifiableMap(Map 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.
Returns:
an unmodifiable view of the specified map.

unmodifiableSortedMap

public static SortedMap unmodifiableSortedMap(SortedMap m)
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 subMap, headMap, or tailMap views, result in an UnsupportedOperationException.

The returned sorted map will be serializable if the specified sorted map is serializable.

Parameters:
m - the sorted map for which an unmodifiable view is to be returned.
Returns:
an unmodifiable view of the specified sorted map.

synchronizedCollection

public static Collection synchronizedCollection(Collection 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 = 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.

Parameters:
c - the collection to be "wrapped" in a synchronized collection.
Returns:
a synchronized view of the specified collection.

synchronizedSet

public static Set synchronizedSet(Set 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 = 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.

Parameters:
s - the set to be "wrapped" in a synchronized set.
Returns:
a synchronized view of the specified set.

synchronizedSortedSet

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

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.

Parameters:
s - the sorted set to be "wrapped" in a synchronized sorted set.
Returns:
a synchronized view of the specified sorted set.

synchronizedList

public static List synchronizedList(List 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 = 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.

Parameters:
list - the list to be "wrapped" in a synchronized list.
Returns:
a synchronized view of the specified list.

synchronizedMap

public static Map synchronizedMap(Map 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 = 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.

Parameters:
m - the map to be "wrapped" in a synchronized map.
Returns:
a synchronized view of the specified map.

synchronizedSortedMap

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

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.

Parameters:
m - the sorted map to be "wrapped" in a synchronized sorted map.
Returns:
a synchronized view of the specified sorted map.

singleton

public static Set singleton(Object o)
Returns an immutable set containing only the specified object. The returned set is serializable.

Parameters:
o - the sole object to be stored in the returned set.
Returns:
an immutable set containing only the specified object.

singletonList

public static List singletonList(Object o)
Returns an immutable list containing only the specified object. The returned list is serializable.

Parameters:
o - the sole object to be stored in the returned list.
Returns:
an immutable list containing only the specified object.

singletonMap

public static Map singletonMap(Object key,
                               Object value)
Returns an immutable map, mapping only the specified key to the specified value. The returned map is serializable.

Parameters:
key - the sole key to be stored in the returned map.
value - the value to which the returned map maps key.
Returns:
an immutable map containing only the specified key-value mapping.

nCopies

public static List nCopies(int n,
                           Object o)

reverseOrder

public static Comparator reverseOrder()

enumeration

public static Enumeration enumeration(Collection c)

list

public static ArrayList list(Enumeration e)


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