java.util.Collections
is new.
java.lang.Object
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.
The methods of this class all throw a
NullPointerException
if the collections
or class objects
provided to them are null.
The documentation for the polymorphic algorithms contained in this class generally includes a brief description of the implementation . Such descriptions should be regarded as implementation notes , rather than parts of the specification . Implementors should feel free to substitute other algorithms, so long as the specification itself is adhered to. (For example, the algorithm used by sort does not have to be a mergesort, but it does have to be stable .)
The "destructive" algorithms contained in this class, that is, the algorithms that modify the collection on which they operate, are specified to throw UnsupportedOperationException if the collection does not support the appropriate mutation primitive(s), such as the set method. These algorithms may, but are not required to, throw this exception if an invocation would have no effect on the collection. For example, invoking the sort method on an unmodifiable list that is already sorted may or may not throw UnsupportedOperationException .
This class is a member of the Java Collections Framework .
| 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
|
addAll
(
Collection
<? super T> c, T[] a)
Adds all of the elements in the specified array to the specified collection.
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static
|
binarySearch
(
List
<? extends T> list, T key)
Searches the specified list for the specified object using the binary search algorithm.
|
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|
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static
|
binarySearch
(
List
<? extends T> list, T key,
Comparator
<? super T> c)
Searches the specified list for the specified object using the binary search algorithm.
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static
|
checkedCollection
(
Collection
<E> c,
Class
<E> type)
Returns a dynamically typesafe view of the specified collection.
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static
|
checkedList
(
List
<E> list,
Class
<E> type)
Returns a dynamically typesafe view of the specified list.
|
|||
|
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|
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static
|
checkedMap
(
Map
<K,V> m,
Class
<K> keyType,
Class
<V> valueType)
Returns a dynamically typesafe view of the specified map.
|
|||
|
|
|
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static
|
checkedSet
(
Set
<E> s,
Class
<E> type)
Returns a dynamically typesafe view of the specified set.
|
|||
|
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|
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static
|
checkedSortedMap
(
SortedMap
<K,V> m,
Class
<K> keyType,
Class
<V> valueType)
Returns a dynamically typesafe view of the specified sorted map.
|
|||
|
|
|
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static
|
checkedSortedSet
(
SortedSet
<E> s,
Class
<E> type)
Returns a dynamically typesafe view of the specified sorted set.
|
|||
|
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static
|
copy
(
List
<? super T> dest,
List
<? extends T> src)
Copies all of the elements from one list into another.
|
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|
static boolean
|
disjoint
Collection
<?> c1,
Collection
Returns
true
if
two
specified
collections have no elements in common.
|
|||
static
|
emptyList
()
|
|||
|
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|
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static
|
emptyMap
()
|
|||
|
|
|
|||
static
|
emptySet
()
|
|||
|
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static
| ||||
|
|
enumeration
Collection
<T> c)
Returns
an enumeration over
collection.
|
|||
static
|
fill
(
List
<? super T> list, T obj)
Replaces all of the elements of the specified list with the specified element.
|
|||
|
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|
static int
|
frequency
<?> c,
Object
Returns
the number
elements in
the specified
collection equal to the specified object.
|
|||
|
static int
|
indexOfSubList
(
List
<?> source,
List
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.
|
|||
|
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|
static int
|
lastIndexOfSubList
(
List
<?> source,
List
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.
|
|||
|
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static
|
list
(
Enumeration
<T> e)
Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration.
|
|||
|
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|
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static
|
max
(
Collection
<? extends T> coll)
Returns the maximum element of the given collection, according to the
natural ordering
of its elements.
|
|||
static
|
max
(
Collection
<? extends T> coll,
Comparator
<? super T> comp)
Returns the maximum element of the given collection, according to the order induced by the specified comparator.
|
|||
static
|
min
(
Collection
<? extends T> coll)
Returns the minimum element of the given collection, according to the
natural ordering
of its elements.
|
|||
static
|
min
(
Collection
<? extends T> coll,
Comparator
<? super T> comp)
Returns the minimum element of the given collection, according to the order induced by the specified comparator.
|
|||
static
|
nCopies
(int n, T o)
Returns an immutable list consisting of
n
copies of the specified object.
|
|||
static
|
replaceAll
(
List
<T> list, T oldVal, T newVal)
Replaces all occurrences of one specified value in a list with another.
|
|||
|
static void
|
reverse
(
List
Reverses the order of the elements in the specified list.
|
|||
|
static
Comparator
<
Object
|
reverseOrder
()
Returns a comparator that imposes the reverse of the
natural ordering
on a collection of objects that implement the
Comparable
interface.
|
|||
static
|
reverseOrder
(
Comparator
<T> cmp)
Returns a comparator that imposes the reverse ordering of the specified comparator.
|
|||
|
static void
|
rotate
(
List
Rotates the elements in the specified list by the specified distance.
|
|||
|
static void
|
shuffle
(
List
Randomly permutes the specified list using a default source of randomness.
|
|||
|
static void
|
shuffle
(
List
<?> list,
Random
Randomly permute the specified list using the specified source of randomness.
|
|||
static
|
singleton
(T o)
Returns an immutable set containing only the specified object.
|
|||
static
|
singletonList
(T o)
Returns an immutable list containing only the specified object.
|
|||
static
|
singletonMap
(K key, V value)
Returns an immutable map, mapping only the specified key to the specified value.
|
|||
static
|
sort
(
List
<T> list)
Sorts the specified list into ascending order, according to the
natural ordering
of its elements.
|
|||
static
|
sort
(
List
<T> list,
Comparator
<? super T> c)
Sorts the specified list according to the order induced by the specified comparator.
|
|||
|
static void
|
swap
(
List
Swaps the elements at the specified positions in the specified list.
|
|||
static
|
synchronizedCollection
(
Collection
<T> c)
Returns a synchronized (thread-safe) collection backed by the specified collection.
|
|||
static
|
synchronizedList
(
List
<T> list)
Returns a synchronized (thread-safe) list backed by the specified list.
|
|||
static
|
synchronizedMap
(
Map
<K,V> m)
Returns a synchronized (thread-safe) map backed by the specified map.
|
|||
static
|
synchronizedSet
(
Set
<T> s)
Returns a synchronized (thread-safe) set backed by the specified set.
|
|||
static
|
synchronizedSortedMap
(
SortedMap
<K,V> m)
Returns a synchronized (thread-safe) sorted map backed by the specified sorted map.
|
|||
static
|
synchronizedSortedSet
(
SortedSet
<T> s)
Returns a synchronized (thread-safe) sorted set backed by the specified sorted set.
|
|||
static
|
unmodifiableCollection
(
Collection
<? extends T> c)
Returns an unmodifiable view of the specified collection.
|
|||
static
|
unmodifiableList
(
List
<? extends T> list)
Returns an unmodifiable view of the specified list.
|
|||
static
|
unmodifiableMap
(
Map
<? extends K,? extends V> m)
Returns an unmodifiable view of the specified map.
|
|||
static
|
unmodifiableSet
(
Set
<? extends T> s)
Returns an unmodifiable view of the specified set.
|
|||
static
|
unmodifiableSortedMap
(
SortedMap
<K,? extends V> m)
Returns an unmodifiable view of the specified sorted map.
|
|||
static
|
unmodifiableSortedSet
(
SortedSet
<T> s)
Returns an unmodifiable view of the specified sorted set.
|
|||
| Methods inherited from class java.lang. Object |
|---|
| clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
| Field Detail |
|---|
public static final Set EMPTY_SET
public static final List EMPTY_LIST
public static final Map EMPTY_MAP
| Method Detail |
|---|
public static voidsort(Listlist)
This sort is guaranteed to be stable : equal elements will not be reordered as a result of the sort.
The specified list must be modifiable, but need not be resizable.
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 2 log(n) performance that would result from attempting to sort a linked list in place.
public staticlist,Comparatorc)
This sort is guaranteed to be stable : equal elements will not be reordered as a result of the sort.
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 2 log(n) performance that would result from attempting to sort a linked list in place.
public static intbinarySearch(Listlist,Objectkey)
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 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.
public staticlist,Objectkey,Comparatorc)
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 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.
public static void reverse(Listlist)
This method runs in linear time.
public static void shuffle(Listlist)
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.
public static void shuffle(Listlist,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.
public static void swap(Listlist,int i, int j)
public staticlist,Objectobj)
This method runs in linear time.
public staticdest,Listsrc)
This method runs in linear time.
public staticcoll)
This method iterates over the entire collection, hence it requires time proportional to the size of the collection.
public staticObjectmin(Collectioncoll,Comparatorcomp)
This method iterates over the entire collection, hence it requires time proportional to the size of the collection.
public staticcoll)
This method iterates over the entire collection, hence it requires time proportional to the size of the collection.
public staticObjectmax(Collectioncoll,Comparatorcomp)
This method iterates over the entire collection, hence it requires time proportional to the size of the collection.
public static void rotate(Listlist,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).
public staticlist,ObjectoldVal,ObjectnewVal)
public static int indexOfSubList(Listsource,Listtarget)
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.
public static int lastIndexOfSubList(Listsource,Listtarget)
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.
public staticc)
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.
public statics)
The returned set will be serializable if the specified set is serializable.
public statics)
The returned sorted set will be serializable if the specified sorted set is serializable.
public staticlist)
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
public staticm)
The returned map will be serializable if the specified map is serializable.
public staticm)
The returned sorted map will be serializable if the specified sorted map is serializable.
public staticc)
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.
public statics)
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.
public statics)
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.
public staticlist)
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.
public staticm)
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.
public staticm)
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.
checkedCollection
Returns a dynamically typesafe view of the specified collection. Any attempt to insert an element of the wrong type will result in an immediate
ClassCastException
. Assuming a collection contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the collection takes place through the view, it is
guaranteed
that the collection cannot contain an incorrectly typed element.
The generics mechanism in the language provides compile-time (static) type checking, but it is possible to defeat this mechanism with unchecked casts. Usually this is not a problem, as the compiler issues warnings on all such unchecked operations. There are, however, times when static type checking alone is not sufficient. For example, suppose a collection is passed to a third-party library and it is imperative that the library code not corrupt the collection by inserting an element of the wrong type.
Another use of dynamically typesafe views is debugging. Suppose a program fails with a
ClassCastException
, indicating that an incorrectly typed element was put into a parameterized collection. Unfortunately, the exception can occur at any time after the erroneous element is inserted, so it typically provides little or no information as to the real source of the problem. If the problem is reproducible, one can quickly determine its source by temporarily modifying the program to wrap the collection with a dynamically typesafe view. For example, this declaration:
Collection<String> c = new HashSet<String>();
may be replaced temporarily by this one:
Collection<String> c = Collections.checkedCollection(
new HashSet<String>(), String.class);
Running the program again will cause it to fail at the point where an incorrectly typed element is inserted into the collection, clearly identifying the source of the probelm. Once the problem is fixed, the modified declaration may be reverted back to the original.
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 a dynamically typesafe view is to be returned
type - the type of element that
c
is permitted to hold
Returns:
a dynamically typesafe view of the specified collection
checkedSet
Returns a dynamically typesafe view of the specified set. Any attempt to insert an element of the wrong type will result in an immediate
ClassCastException
. Assuming a set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the set takes place through the view, it is
guaranteed
that the set cannot contain an incorrectly typed element.
A discussion of the use of dynamically typesafe views may be found in the documentation for the #checkedCollection() method.
The returned set will be serializable if the specified set is serializable.
Parameters:
s - the set for which a dynamically typesafe view is to be returned
type - the type of element that
s
is permitted to hold
Returns:
a dynamically typesafe view of the specified set
checkedSortedSet
Returns a dynamically typesafe view of the specified sorted set. Any attempt to insert an element of the wrong type will result in an immediate
ClassCastException
. Assuming a sorted set contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the sorted set takes place through the view, it is
guaranteed
that the sorted set cannot contain an incorrectly typed element.
A discussion of the use of dynamically typesafe views may be found in the documentation for the #checkedCollection() method.
The returned sorted set will be serializable if the specified sorted set is serializable.
Parameters:
s - the sorted set for which a dynamically typesafe view is to be returned
type - the type of element that
s
is permitted to hold
Returns:
a dynamically typesafe view of the specified sorted set
checkedList
Returns a dynamically typesafe view of the specified list. Any attempt to insert an element of the wrong type will result in an immediate
ClassCastException
. Assuming a list contains no incorrectly typed elements prior to the time a dynamically typesafe view is generated, and that all subsequent access to the list takes place through the view, it is
guaranteed
that the list cannot contain an incorrectly typed element.
A discussion of the use of dynamically typesafe views may be found in the documentation for the #checkedCollection() method.
The returned list will be serializable if the specified list is serializable.
Parameters:
list - the list for which a dynamically typesafe view is to be returned
type - the type of element that
list
is permitted to hold
Returns:
a dynamically typesafe view of the specified list
checkedMap
Returns a dynamically typesafe view of the specified map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate
ClassCastException
. Similarly, any attempt to modify the value currently associated with a key will result in an immediate
ClassCastException
, whether the modification is attempted directly through the map itself, or through a Map#Entry instance obtained from the map's
entry set
view.
Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its colleciton views), it is
guaranteed
that the map cannot contain an incorrectly typed key or value.
A discussion of the use of dynamically typesafe views may be found in the documentation for the #checkedCollection() method.
The returned map will be serializable if the specified map is serializable.
Parameters:
m - the map for which a dynamically typesafe view is to be returned
keyType - the type of key that
m
is permitted to hold
valueType - the type of value that
m
is permitted to hold
Returns:
a dynamically typesafe view of the specified map
checkedSortedMap
Returns a dynamically typesafe view of the specified sorted map. Any attempt to insert a mapping whose key or value have the wrong type will result in an immediate
ClassCastException
. Similarly, any attempt to modify the value currently associated with a key will result in an immediate
ClassCastException
, whether the modification is attempted directly through the map itself, or through a Map#Entry instance obtained from the map's
entry set
view.
Assuming a map contains no incorrectly typed keys or values prior to the time a dynamically typesafe view is generated, and that all subsequent access to the map takes place through the view (or one of its colleciton views), it is
guaranteed
that the map cannot contain an incorrectly typed key or value.
A discussion of the use of dynamically typesafe views may be found in the documentation for the #checkedCollection() method.
The returned map will be serializable if the specified map is serializable.
Parameters:
m - the map for which a dynamically typesafe view is to be returned
keyType - the type of key that
m
is permitted to hold
valueType - the type of value that
m
is permitted to hold
Returns:
a dynamically typesafe view of the specified map
emptySet
emptyList
emptyMap
public static(Objecto)
public static(Objecto)
public static(Objectkey,Objectvalue)
public static(int n,Objecto)
public static Comparator
Arrays.sort(a, Collections.reverseOrder());sorts the array in reverse-lexicographic (alphabetical) order.
The returned comparator is serializable.
reverseOrder
Returns a comparator that imposes the reverse ordering of the specified comparator. If the specified comparator is null, this method is equivalent to
reverseOrder()
(in other words, it returns a comparator that imposes the reverse of the
natural ordering
on a collection of objects that implement the Comparable interface).
The returned comparator is serializable (assuming the specified comparator is also serializable or null).
Returns:
a comparator that imposes the reverse ordering of the specified comparator.
Since:
1.5
public staticc)
public statice)
frequency
Returns the number of elements in the specified collection equal to the specified object. More formally, returns the number of elements
e
in the collection such that
(o == null ? e == null : o.equals(e))
.
Parameters:
c - the collection in which to determine the frequency of
o
o - the object whose frequency is to be determined
Throws:
NullPointerException
- if
c
is null
Since:
1.5
disjoint
Returns
true
if the two specified collections have no elements in common.
Care must be exercised if this method is used on collections that do not comply with the general contract for
Collection
. Implementations may elect to iterate over either collection and test for containment in the other collection (or to perform any equivalent computation). If either collection uses a nonstandard equality test (as does a
SortedSet
whose ordering is not
compatible with equals
, or the key set of an
IdentityHashMap
), both collections must use the same nonstandard equality test, or the result of this method is undefined.
Note that it is permissible to pass the same collection in both parameters, in which case the method will return true if and only if the collection is empty.
Parameters:
c1 - a collection
c2 - a collection
Throws:
NullPointerException
- if either collection is null
Since:
1.5
addAll
Adds all of the elements in the specified array to the specified collection. The behavior of this convenience method is identical to that of
c.addAll(Arrays.asList(a))
, but this method is likely to run significantly faster under most implementations.
Parameters:
c - the colleciton into which to insert the elements of
a
a - the array whose elements to insert into
c
Returns:
true
if the collection changed as a result of the call
Throws:
UnsupportedOperationException
- if
c
does not support the
add
method
NullPointerException
- if
a
contains one or more null elements and
c
does not support null elements, or if
c
or
a
are
null
IllegalArgumentException
- some aspect of an element of
a
prevents it from being added to
c
Since:
1.5
See Also:
Collection.addAll(Collection)