Movatterモバイル変換

Type Parameters:
E - the type of elements in this collection
All Superinterfaces:
Iterable<E>
All Known Subinterfaces:
BeanContext,BeanContextServices,BlockingDeque<E>,BlockingQueue<E>,Deque<E>,List<E>,NavigableSet<E>,Queue<E>,Set<E>,SortedSet<E>,TransferQueue<E>
All Known Implementing Classes:
AbstractCollection,AbstractList,AbstractQueue,AbstractSequentialList,AbstractSet,ArrayBlockingQueue,ArrayDeque,ArrayList,AttributeList,BeanContextServicesSupport,BeanContextSupport,ConcurrentLinkedDeque,ConcurrentLinkedQueue,ConcurrentSkipListSet,CopyOnWriteArrayList,CopyOnWriteArraySet,DelayQueue,EnumSet,HashSet,JobStateReasons,LinkedBlockingDeque,LinkedBlockingQueue,LinkedHashSet,LinkedList,LinkedTransferQueue,PriorityBlockingQueue,PriorityQueue,RoleList,RoleUnresolvedList,Stack,SynchronousQueue,TreeSet,Vector
```
public interfaceCollection<E>extendsIterable<E>
```
The root interface in thecollection hierarchy. A collection represents a group of objects, known as itselements. Some collections allow duplicate elements and others do not. Some are ordered and others unordered. The JDK does not provide anydirect implementations of this interface: it provides implementations of more specific subinterfaces likeSet andList. This interface is typically used to pass collections around and manipulate them where maximum generality is desired.
Bags ormultisets (unordered collections that may contain duplicate elements) should implement this interface directly.
All general-purposeCollection implementation classes (which typically implementCollection indirectly through one of its subinterfaces) should provide two "standard" constructors: a void (no arguments) constructor, which creates an empty collection, and a constructor with a single argument of typeCollection, which creates a new collection with the same elements as its argument. In effect, the latter constructor allows the user to copy any collection, producing an equivalent collection of the desired implementation type. There is no way to enforce this convention (as interfaces cannot contain constructors) but all of the general-purposeCollection implementations in the Java platform libraries comply.
The "destructive" methods contained in this interface, that is, the methods that modify the collection on which they operate, are specified to throwUnsupportedOperationException if this collection does not support the operation. If this is the case, these methods may, but are not required to, throw anUnsupportedOperationException if the invocation would have no effect on the collection. For example, invoking theaddAll(Collection) method on an unmodifiable collection may, but is not required to, throw the exception if the collection to be added is empty.
Some collection implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typicallyNullPointerException orClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the collection may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.
It is up to each collection to determine its own synchronization policy. In the absence of a stronger guarantee by the implementation, undefined behavior may result from the invocation of any method on a collection that is being mutated by another thread; this includes direct invocations, passing the collection to a method that might perform invocations, and using an existing iterator to examine the collection.
Many methods in Collections Framework interfaces are defined in terms of the equals method. For example, the specification for thecontains(Object o) method says: "returnstrue if and only if this collection contains at least one elemente such that(o==null ? e==null : o.equals(e))." This specification shouldnot be construed to imply that invokingCollection.contains with a non-null argumento will causeo.equals(e) to be invoked for any elemente. Implementations are free to implement optimizations whereby theequals invocation is avoided, for example, by first comparing the hash codes of the two elements. (TheObject.hashCode() specification guarantees that two objects with unequal hash codes cannot be equal.) More generally, implementations of the various Collections Framework interfaces are free to take advantage of the specified behavior of underlyingObject methods wherever the implementor deems it appropriate.
This interface is a member of the Java Collections Framework.
Since:
1.2
See Also:
Set,List,Map,SortedSet,SortedMap,HashSet,TreeSet,ArrayList,LinkedList,Vector,Collections,Arrays,AbstractCollection

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`add(E e)` Ensures that this collection contains the specified element (optional operation).
`boolean`	`addAll(Collection<? extendsE> c)` Adds all of the elements in the specified collection to this collection (optional operation).
`void`	`clear()` Removes all of the elements from this collection (optional operation).
`boolean`	`contains(Object o)` Returns`true` if this collection contains the specified element.
`boolean`	`containsAll(Collection<?> c)` Returns`true` if this collection contains all of the elements in the specified collection.
`boolean`	`equals(Object o)` Compares the specified object with this collection for equality.
`int`	`hashCode()` Returns the hash code value for this collection.
`boolean`	`isEmpty()` Returns`true` if this collection contains no elements.
`Iterator<E>`	`iterator()` Returns an iterator over the elements in this collection.
`boolean`	`remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`boolean`	`removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`boolean`	`retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`int`	`size()` Returns the number of elements in this collection.
`Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`<T> T[]`	`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
  - size
```
int size()
```
    Returns the number of elements in this collection. If this collection contains more thanInteger.MAX_VALUE elements, returnsInteger.MAX_VALUE.
    Returns:
    the number of elements in this collection
  - isEmpty
```
boolean isEmpty()
```
    Returnstrue if this collection contains no elements.
    Returns:
    true if this collection contains no elements
  - contains
```
boolean contains(Object o)
```
    Returnstrue if this collection contains the specified element. More formally, returnstrue if and only if this collection contains at least one elemente such that(o==null ? e==null : o.equals(e)).
    Parameters:
    o - element whose presence in this collection is to be tested
    Returns:
    true if this collection contains the specified element
    Throws:
    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
```
Iterator<E> iterator()
```
    Returns an iterator over the elements in this collection. There are no guarantees concerning the order in which the elements are returned (unless this collection is an instance of some class that provides a guarantee).
    Specified by:
    iterator in interface Iterable<E>
    Returns:
    anIterator over the elements in this collection
  - toArray
```
Object[] toArray()
```
    Returns an array containing all of the elements in this collection. 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.
    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.
    Returns:
    an array containing all of the elements in this collection
  - toArray
```
<T> T[] 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. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.
    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 tonull. (This is useful in determining the length of this collectiononly if the caller knows that this collection does not contain anynull 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 thetoArray() 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.
    Supposex is a collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array ofString:
```
     String[] y = x.toArray(new String[0]);
```
    Note thattoArray(new Object[0]) is identical in function totoArray().
    Parameters:
    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.
    Returns:
    an array containing all of the elements in this collection
    Throws:
    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 null
  - add
```
boolean add(E e)
```
    Ensures that this collection contains the specified element (optional operation). Returnstrue if this collection changed as a result of the call. (Returnsfalse if this collection does not permit duplicates and already contains the specified element.)
    Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to addnull 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, itmust throw an exception (rather than returningfalse). This preserves the invariant that a collection always contains the specified element after this call returns.
    Parameters:
    e - element whose presence in this collection is to be ensured
    Returns:
    true if this collection changed as a result of the call
    Throws:
    UnsupportedOperationException - if theadd 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 restrictions
  - remove
```
boolean remove(Object o)
```
    Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an elemente such that(o==null ? e==null : o.equals(e)), if this collection contains one or more such elements. Returnstrue if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).
    Parameters:
    o - element to be removed from this collection, if present
    Returns:
    true if an element was removed as a result of this call
    Throws:
    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 theremove operation is not supported by this collection
  - containsAll
```
boolean containsAll(Collection<?> c)
```
    Returnstrue if this collection contains all of the elements in the specified collection.
    Parameters:
    c - collection to be checked for containment in this collection
    Returns:
    true if this collection contains all of the elements in the specified collection
    Throws:
    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 null.
    See Also:
    contains(Object)
  - addAll
```
boolean addAll(Collection<? extendsE> c)
```
    Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)
    Parameters:
    c - collection containing elements to be added to this collection
    Returns:
    true if this collection changed as a result of the call
    Throws:
    UnsupportedOperationException - if theaddAll 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 restrictions
    See Also:
    add(Object)
  - removeAll
```
boolean removeAll(Collection<?> c)
```
    Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
    Parameters:
    c - collection containing elements to be removed from this collection
    Returns:
    true if this collection changed as a result of the call
    Throws:
    UnsupportedOperationException - if theremoveAll 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 null
    See Also:
    remove(Object),contains(Object)
  - retainAll
```
boolean retainAll(Collection<?> c)
```
    Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
    Parameters:
    c - collection containing elements to be retained in this collection
    Returns:
    true if this collection changed as a result of the call
    Throws:
    UnsupportedOperationException - if theretainAll 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 null
    See Also:
    remove(Object),contains(Object)
  - clear
```
void clear()
```
    Removes all of the elements from this collection (optional operation). The collection will be empty after this method returns.
    Throws:
    UnsupportedOperationException - if theclear operation is not supported by this collection
  - equals
```
boolean equals(Object o)
```
    Compares the specified object with this collection for equality.
    While theCollection interface adds no stipulations to the general contract for theObject.equals, programmers who implement theCollection interface "directly" (in other words, create a class that is aCollection but is not aSet or aList) must exercise care if they choose to override theObject.equals. It is not necessary to do so, and the simplest course of action is to rely onObject's implementation, but the implementor may wish to implement a "value comparison" in place of the default "reference comparison." (TheList andSet interfaces mandate such value comparisons.)
    The general contract for theObject.equals method states that equals must be symmetric (in other words,a.equals(b) if and only ifb.equals(a)). The contracts forList.equals andSet.equals state that lists are only equal to other lists, and sets to other sets. Thus, a customequals method for a collection class that implements neither theList norSet interface must returnfalse 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 theSet andList interfaces.)
    Overrides:
    equals in class Object
    Parameters:
    o - object to be compared for equality with this collection
    Returns:
    true if the specified object is equal to this collection
    See Also:
    Object.equals(Object),Set.equals(Object),List.equals(Object)
  - hashCode
```
int hashCode()
```
    Returns the hash code value for this collection. While theCollection interface adds no stipulations to the general contract for theObject.hashCode method, programmers should take note that any class that overrides theObject.equals method must also override theObject.hashCode method in order to satisfy the general contract for theObject.hashCode method. In particular,c1.equals(c2) implies thatc1.hashCode()==c2.hashCode().
    Overrides:
    hashCode in class Object
    Returns:
    the hash code value for this collection
    See Also:
    Object.hashCode(),Object.equals(Object)

Movatterモバイル変換

Interface Collection<E>

Method Summary

Method Detail

size

isEmpty

contains

iterator

toArray

toArray

add

remove

containsAll

addAll

removeAll

retainAll

clear

equals

hashCode