程序包 java.util.concurrent

类 ConcurrentHashMap.KeySetView<K,V>

java.lang.Object

java.util.concurrent.ConcurrentHashMap.KeySetView<K,V>

所有已实现的接口:

Serializable, Iterable<K>, Collection<K>, Set<K>

封闭类:

ConcurrentHashMap<K,V>

public static class ConcurrentHashMap.KeySetView<K,V>
extends Object
implements Set<K>, Collection<K>, Serializable

A view of a ConcurrentHashMap as a Set of keys, in which additions may optionally be enabled by mapping to a common value. This class cannot be directly instantiated. See keySet(), keySet(V), newKeySet(), newKeySet(int).

从以下版本开始:

1.8

另请参阅:

序列化表格

方法概要

限定符和类型	方法	说明
boolean	add(K e)	Adds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.
boolean	addAll(Collection<? extends K> c)	Adds all of the elements in the specified collection to this set, as if by calling add(K) on each one.
void	clear()	Removes all of the elements from this view, by removing all the mappings from the map backing this view.
boolean	contains(Object o)	Returns true if this set contains the specified element.
boolean	containsAll(Collection<?> c)	Returns true if this set contains all of the elements of the specified collection.
boolean	equals(Object o)	Indicates whether some other object is "equal to" this one.
void	forEach(Consumer<? super K> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
ConcurrentHashMap<K,V>	getMap()	Returns the map backing this view.
V	getMappedValue()	Returns the default mapped value for additions, or null if additions are not supported.
int	hashCode()	Returns a hash code value for the object.
boolean	isEmpty()	Returns true if this set contains no elements.
Iterator<K>	iterator()	Returns an iterator over the elements in this set.
boolean	remove(Object o)	Removes the key from this map view, by removing the key (and its corresponding value) from the backing map.
boolean	removeAll(Collection<?> c)	Removes from this set all of its elements that are contained in the specified collection (optional operation).
boolean	retainAll(Collection<?> c)	Retains only the elements in this set that are contained in the specified collection (optional operation).
int	size()	Returns the number of elements in this set (its cardinality).
Spliterator<K>	spliterator()	Creates a Spliterator over the elements in this set.
Object[]	toArray()	Returns an array containing all of the elements in this set.
<T> T[]	toArray(T[] a)	Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array.
String	toString()	Returns a string representation of this collection.

从接口继承的方法 java.util.Collection

parallelStream, removeIf, stream

从类继承的方法 java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

方法详细资料

getMappedValue

public V getMappedValue()

Returns the default mapped value for additions, or null if additions are not supported.

返回:

the default mapped value for additions, or null if not supported

contains

public boolean contains(Object o)

Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)).

指定者:

contains 在接口中 Collection<K>

指定者:

contains 在接口中 Set<K>

参数:

o - element whose presence in this set is to be tested

返回:

true if this set contains the specified element

抛出:

NullPointerException - if the specified key is null

remove

public boolean remove(Object o)

Removes the key from this map view, by removing the key (and its corresponding value) from the backing map. This method does nothing if the key is not in the map.

指定者:

remove 在接口中 Collection<K>

指定者:

remove 在接口中 Set<K>

参数:

o - the key to be removed from the backing map

返回:

true if the backing map contained the specified key

抛出:

NullPointerException - if the specified key is null

iterator

public Iterator<K> iterator()

从接口复制的说明: Set

Returns an iterator over the elements in this set. The elements are returned in no particular order (unless this set is an instance of some class that provides a guarantee).

指定者:

iterator 在接口中 Collection<K>

指定者:

iterator 在接口中 Iterable<K>

指定者:

iterator 在接口中 Set<K>

返回:

an iterator over the keys of the backing map

add

public boolean add(K e)

Adds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.

指定者:

add 在接口中 Collection<K>

指定者:

add 在接口中 Set<K>

参数:

e - key to be added

返回:

true if this set changed as a result of the call

抛出:

NullPointerException - if the specified key is null

UnsupportedOperationException - if no default mapped value for additions was provided

addAll

public boolean addAll(Collection<? extends K> c)

Adds all of the elements in the specified collection to this set, as if by calling add(K) on each one.

指定者:

addAll 在接口中 Collection<K>

指定者:

addAll 在接口中 Set<K>

参数:

c - the elements to be inserted into this set

返回:

true if this set changed as a result of the call

抛出:

NullPointerException - if the collection or any of its elements are null

UnsupportedOperationException - if no default mapped value for additions was provided

另请参阅:

Set.add(Object)

hashCode

public int hashCode()

从类复制的说明: Object

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

• Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
• If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
• It is not required that if two objects are unequal according to the Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java™ programming language.)

指定者:

hashCode 在接口中 Collection<K>

指定者:

hashCode 在接口中 Set<K>

覆盖:

hashCode 在类中 Object

返回:

a hash code value for this object.

另请参阅:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

equals

public boolean equals(Object o)

从类复制的说明: Object

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
• For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

指定者:

equals 在接口中 Collection<K>

指定者:

equals 在接口中 Set<K>

覆盖:

equals 在类中 Object

参数:

o - the reference object with which to compare.

返回:

true if this object is the same as the obj argument; false otherwise.

另请参阅:

Object.hashCode(), HashMap

spliterator

public Spliterator<K> spliterator()

从接口复制的说明: Set

Creates a Spliterator over the elements in this set.

The Spliterator reports Spliterator#DISTINCT. Implementations should document the reporting of additional characteristic values.

指定者:

spliterator 在接口中 Collection<K>

指定者:

spliterator 在接口中 Iterable<K>

指定者:

spliterator 在接口中 Set<K>

返回:

a Spliterator over the elements in this set

forEach

public void forEach(Consumer<? super K> action)

从接口复制的说明: Iterable

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of iteration (if an iteration order is specified). Exceptions thrown by the action are relayed to the caller.

指定者:

forEach 在接口中 Iterable<K>

参数:

action - The action to be performed for each element

removeAll

public final boolean removeAll(Collection<?> c)

从接口复制的说明: Set

Removes from this set all of its elements that are contained in the specified collection (optional operation). If the specified collection is also a set, this operation effectively modifies this set so that its value is the asymmetric set difference of the two sets.

指定者:

removeAll 在接口中 Collection<K>

指定者:

removeAll 在接口中 Set<K>

参数:

c - collection containing elements to be removed from this set

返回:

true if this set changed as a result of the call

另请参阅:

Set.remove(Object), Set.contains(Object)

size

public final int size()

从接口复制的说明: Set

Returns the number of elements in this set (its cardinality). If this set contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

指定者:

size 在接口中 Collection<K>

指定者:

size 在接口中 Set<K>

返回:

the number of elements in this set (its cardinality)

containsAll

public final boolean containsAll(Collection<?> c)

从接口复制的说明: Set

Returns true if this set contains all of the elements of the specified collection. If the specified collection is also a set, this method returns true if it is a subset of this set.

指定者:

containsAll 在接口中 Collection<K>

指定者:

containsAll 在接口中 Set<K>

参数:

c - collection to be checked for containment in this set

返回:

true if this set contains all of the elements of the specified collection

另请参阅:

Set.contains(Object)

clear

public final void clear()

Removes all of the elements from this view, by removing all the mappings from the map backing this view.

指定者:

clear 在接口中 Collection<K>

指定者:

clear 在接口中 Set<K>

isEmpty

public final boolean isEmpty()

从接口复制的说明: Set

Returns true if this set contains no elements.

指定者:

isEmpty 在接口中 Collection<K>

指定者:

isEmpty 在接口中 Set<K>

返回:

true if this set contains no elements

toArray

public final Object[] toArray()

从接口复制的说明: Set

Returns an array containing all of the elements in this set. If this set 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 set. (In other words, this method must allocate a new array even if this set 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.

指定者:

toArray 在接口中 Collection<K>

指定者:

toArray 在接口中 Set<K>

返回:

an array containing all the elements in this set

toArray

public final <T> T[] toArray(T[] a)

从接口复制的说明: Set

Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. If the set 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 set.

If this set fits in the specified array with room to spare (i.e., the array has more elements than this set), the element in the array immediately following the end of the set is set to null. (This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements.)

If this set 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 Set.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 set known to contain only strings. The following code can be used to dump the set 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().

指定者:

toArray 在接口中 Collection<K>

指定者:

toArray 在接口中 Set<K>

类型参数:

T - the runtime type of the array to contain the collection

参数:

a - the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

返回:

an array containing all the elements in this set

toString

public final String toString()

Returns a string representation of this collection. The string representation consists of the string representations of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String#valueOf(Object).

覆盖:

toString 在类中 Object

返回:

a string representation of this collection

getMap

public ConcurrentHashMap<K,V> getMap()

Returns the map backing this view.

返回:

the map backing this view

retainAll

public final boolean retainAll(Collection<?> c)

从接口复制的说明: Set

Retains only the elements in this set that are contained in the specified collection (optional operation). In other words, removes from this set all of its elements that are not contained in the specified collection. If the specified collection is also a set, this operation effectively modifies this set so that its value is the intersection of the two sets.

指定者:

retainAll 在接口中 Collection<K>

指定者:

retainAll 在接口中 Set<K>

参数:

c - collection containing elements to be retained in this set

返回:

true if this set changed as a result of the call

另请参阅:

Set.remove(Object)