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Préférences
Moteurs de recherche
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JavaTM 2 Platform Std. Ed. v1.6.0
java.util
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Method Summary | ||
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boolean |
add(E e)
Ensures that this collection contains the specified element (optional operation). |
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boolean |
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this collection (optional operation). |
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void |
clear()
Removes all of the elements from this collection (optional operation). |
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boolean |
contains(Object o)
Returns true if this collection contains the specified element. |
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boolean |
containsAll(Collection<?> c)
Returns true if this collection contains all of the elements in the specified collection. |
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boolean |
equals(Object o)
Compares the specified object with this collection for equality. |
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int |
hashCode()
Returns the hash code value for this collection. |
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boolean |
isEmpty()
Returns true if this collection contains no elements. |
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Iterator<E> |
iterator()
Returns an iterator over the elements in this collection. |
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boolean |
remove(Object o)
Removes a single instance of the specified element from this collection, if it is present (optional operation). |
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boolean |
removeAll(Collection<?> c)
Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
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boolean |
retainAll(Collection<?> c)
Retains only the elements in this collection that are contained in the specified collection (optional operation). |
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int |
size()
Returns the number of elements in this collection. |
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Object[] |
toArray()
Returns an array containing all of the elements in this collection. |
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toArray(T[] a)
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. |
Method Detail |
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int size()
boolean isEmpty()
boolean contains(Object o)
o
- element whose presence in this collection is to be tested
ClassCastException
- if the type of the specified element
is incompatible with this collection (optional)
NullPointerException
- if the specified element is null and this
collection does not permit null elements (optional)Iterator<E> iterator()
Object[] toArray()
The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
<T> T[] toArray(T[] a)
If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
Like the toArray()
method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that toArray(new Object[0]) is identical in function to toArray().
a
- the array into which the elements of this collection are to be
stored, if it is big enough; otherwise, a new array of the same
runtime type is allocated for this purpose.
ArrayStoreException
- if the runtime type of the specified array
is not a supertype of the runtime type of every element in
this collection
NullPointerException
- if the specified array is nullboolean add(E e)
Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.
If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.
e
- element whose presence in this collection is to be ensured
UnsupportedOperationException
- if the add operation
is not supported by this collection
ClassCastException
- if the class of the specified element
prevents it from being added to this collection
NullPointerException
- if the specified element is null and this
collection does not permit null elements
IllegalArgumentException
- if some property of the element
prevents it from being added to this collection
IllegalStateException
- if the element cannot be added at this
time due to insertion restrictionsboolean remove(Object o)
o
- element to be removed from this collection, if present
ClassCastException
- if the type of the specified element
is incompatible with this collection (optional)
NullPointerException
- if the specified element is null and this
collection does not permit null elements (optional)
UnsupportedOperationException
- if the remove operation
is not supported by this collectionboolean containsAll(Collection<?> c)
c
- collection to be checked for containment in this collection
ClassCastException
- if the types of one or more elements
in the specified collection are incompatible with this
collection (optional)
NullPointerException
- if the specified collection contains one
or more null elements and this collection does not permit null
elements (optional), or if the specified collection is nullcontains(Object)
boolean addAll(Collection<? extends E> c)
c
- collection containing elements to be added to this collection
UnsupportedOperationException
- if the addAll operation
is not supported by this collection
ClassCastException
- if the class of an element of the specified
collection prevents it from being added to this collection
NullPointerException
- if the specified collection contains a
null element and this collection does not permit null elements,
or if the specified collection is null
IllegalArgumentException
- if some property of an element of the
specified collection prevents it from being added to this
collection
IllegalStateException
- if not all the elements can be added at
this time due to insertion restrictionsadd(Object)
boolean removeAll(Collection<?> c)
c
- collection containing elements to be removed from this collection
UnsupportedOperationException
- if the removeAll method
is not supported by this collection
ClassCastException
- if the types of one or more elements
in this collection are incompatible with the specified
collection (optional)
NullPointerException
- if this collection contains one or more
null elements and the specified collection does not support
null elements (optional), or if the specified collection is nullremove(Object)
,
contains(Object)
boolean retainAll(Collection<?> c)
c
- collection containing elements to be retained in this collection
UnsupportedOperationException
- if the retainAll operation
is not supported by this collection
ClassCastException
- if the types of one or more elements
in this collection are incompatible with the specified
collection (optional)
NullPointerException
- if this collection contains one or more
null elements and the specified collection does not permit null
elements (optional), or if the specified collection is nullremove(Object)
,
contains(Object)
void clear()
UnsupportedOperationException
- if the clear operation
is not supported by this collectionboolean equals(Object o)
While the Collection interface adds no stipulations to the general contract for the Object.equals, programmers who implement the Collection interface "directly" (in other words, create a class that is a Collection but is not a Set or a List) must exercise care if they choose to override the Object.equals. It is not necessary to do so, and the simplest course of action is to rely on Object's implementation, but the implementor may wish to implement a "value comparison" in place of the default "reference comparison." (The List and Set interfaces mandate such value comparisons.)
The general contract for the Object.equals method states that equals must be symmetric (in other words, a.equals(b) if and only if b.equals(a)). The contracts for List.equals and Set.equals state that lists are only equal to other lists, and sets to other sets. Thus, a custom equals method for a collection class that implements neither the List nor Set interface must return false when this collection is compared to any list or set. (By the same logic, it is not possible to write a class that correctly implements both the Set and List interfaces.)
o
- object to be compared for equality with this collection
Object.equals(Object)
,
Set.equals(Object)
,
List.equals(Object)
int hashCode()
Object.hashCode()
,
Object.equals(Object)