程序包 java.util

类 AbstractMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

类型参数:

K - the type of keys maintained by this map

V - the type of mapped values

所有已实现的接口:

Map<K,V>

直接已知子类:

ConcurrentHashMap, ConcurrentSkipListMap, EnumMap, HashMap, IdentityHashMap, TreeMap, WeakHashMap

public abstract class AbstractMap<K,V>
extends Object
implements Map<K,V>

This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.

To implement an unmodifiable map, the programmer needs only to extend this class and provide an implementation for the entrySet method, which returns a set-view of the map's mappings. Typically, the returned set will, in turn, be implemented atop AbstractSet. This set should not support the add or remove methods, and its iterator should not support the remove method.

To implement a modifiable map, the programmer must additionally override this class's put method (which otherwise throws an UnsupportedOperationException), and the iterator returned by entrySet().iterator() must additionally implement its remove method.

The programmer should generally provide a void (no argument) and map constructor, as per the recommendation in the Map interface specification.

The documentation for each non-abstract method in this class describes its implementation in detail. Each of these methods may be overridden if the map being implemented admits a more efficient implementation.

This class is a member of the Java Collections Framework.

从以下版本开始:

1.2

另请参阅:

Map, Collection

嵌套类概要

嵌套类

限定符和类型	类	说明
static class	AbstractMap.SimpleEntry<K,V>	An Entry maintaining a key and a value.
static class	AbstractMap.SimpleImmutableEntry<K,V>	An Entry maintaining an immutable key and value.

从接口继承的嵌套类/接口 java.util.Map

Map.Entry<K,V>

构造器概要

构造器

限定符	构造器	说明
protected	AbstractMap()	Sole constructor.

方法概要

限定符和类型	方法	说明
void	clear()	Removes all of the mappings from this map (optional operation).
protected Object	clone()	Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.
boolean	containsKey(Object key)	Returns true if this map contains a mapping for the specified key.
boolean	containsValue(Object value)	Returns true if this map maps one or more keys to the specified value.
abstract Set<Map.Entry<K,V>>	entrySet()	Returns a Set view of the mappings contained in this map.
boolean	equals(Object o)	Compares the specified object with this map for equality.
V	get(Object key)	Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
int	hashCode()	Returns the hash code value for this map.
boolean	isEmpty()	Returns true if this map contains no key-value mappings.
Set<K>	keySet()	Returns a Set view of the keys contained in this map.
V	put(K key, V value)	Associates the specified value with the specified key in this map (optional operation).
void	putAll(Map<? extends K,? extends V> m)	Copies all of the mappings from the specified map to this map (optional operation).
V	remove(Object key)	Removes the mapping for a key from this map if it is present (optional operation).
int	size()	Returns the number of key-value mappings in this map.
String	toString()	Returns a string representation of this map.
Collection<V>	values()	Returns a Collection view of the values contained in this map.

从接口继承的方法 java.util.Map

compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

从类继承的方法 java.lang.Object

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

构造器详细资料

AbstractMap

protected AbstractMap()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

方法详细资料

size

public int size()

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

指定者:

size 在接口中 Map<K,V>

返回:

the number of key-value mappings in this map

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings.

指定者:

isEmpty 在接口中 Map<K,V>

返回:

true if this map contains no key-value mappings

containsValue

public boolean containsValue(Object value)

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the map size for most implementations of the Map interface.

指定者:

containsValue 在接口中 Map<K,V>

参数:

value - value whose presence in this map is to be tested

返回:

true if this map maps one or more keys to the specified value

抛出:

ClassCastException - if the value is of an inappropriate type for this map (optional)

NullPointerException - if the specified value is null and this map does not permit null values (optional)

containsKey

public boolean containsKey(Object key)

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

指定者:

containsKey 在接口中 Map<K,V>

参数:

key - key whose presence in this map is to be tested

返回:

true if this map contains a mapping for the specified key

抛出:

ClassCastException - if the key is of an inappropriate type for this map (optional)

NullPointerException - if the specified key is null and this map does not permit null keys (optional)

get

public V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that (key==null ? k==null : key.equals(k)), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

If this map permits null values, then a return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

指定者:

get 在接口中 Map<K,V>

参数:

key - the key whose associated value is to be returned

返回:

the value to which the specified key is mapped, or null if this map contains no mapping for the key

抛出:

ClassCastException - if the key is of an inappropriate type for this map (optional)

NullPointerException - if the specified key is null and this map does not permit null keys (optional)

put

public V put(K key,
             V value)

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)

指定者:

put 在接口中 Map<K,V>

参数:

key - key with which the specified value is to be associated

value - value to be associated with the specified key

返回:

the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)

抛出:

UnsupportedOperationException - if the put operation is not supported by this map

ClassCastException - if the class of the specified key or value prevents it from being stored in this map

NullPointerException - if the specified key or value is null and this map does not permit null keys or values

IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

remove

public V remove(Object key)

Removes the mapping for a key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.

If this map permits null values, then a return value of null does not necessarily indicate that the map contained no mapping for the key; it's also possible that the map explicitly mapped the key to null.

The map will not contain a mapping for the specified key once the call returns.

指定者:

remove 在接口中 Map<K,V>

参数:

key - key whose mapping is to be removed from the map

返回:

the previous value associated with key, or null if there was no mapping for key.

抛出:

UnsupportedOperationException - if the remove operation is not supported by this map

ClassCastException - if the key is of an inappropriate type for this map (optional)

NullPointerException - if the specified key is null and this map does not permit null keys (optional)

putAll

public void putAll(Map<? extends K,? extends V> m)

Copies all of the mappings from the specified map to this map (optional operation). The effect of this call is equivalent to that of calling put(k, v) on this map once for each mapping from key k to value v in the specified map. The behavior of this operation is undefined if the specified map is modified while the operation is in progress.

指定者:

putAll 在接口中 Map<K,V>

参数:

m - mappings to be stored in this map

抛出:

UnsupportedOperationException - if the putAll operation is not supported by this map

ClassCastException - if the class of a key or value in the specified map prevents it from being stored in this map

NullPointerException - if the specified map is null, or if this map does not permit null keys or values, and the specified map contains null keys or values

IllegalArgumentException - if some property of a key or value in the specified map prevents it from being stored in this map

clear

public void clear()

Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.

指定者:

clear 在接口中 Map<K,V>

抛出:

UnsupportedOperationException - if the clear operation is not supported by this map

keySet

public Set<K> keySet()

Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

指定者:

keySet 在接口中 Map<K,V>

返回:

a set view of the keys contained in this map

values

public Collection<V> values()

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

指定者:

values 在接口中 Map<K,V>

返回:

a collection view of the values contained in this map

entrySet

public abstract Set<Map.Entry<K,V>> entrySet()

从接口复制的说明: Map

Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

指定者:

entrySet 在接口中 Map<K,V>

返回:

a set view of the mappings contained in this map

equals

public boolean equals(Object o)

Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

指定者:

equals 在接口中 Map<K,V>

覆盖:

equals 在类中 Object

参数:

o - object to be compared for equality with this map

返回:

true if the specified object is equal to this map

另请参阅:

Object.hashCode(), HashMap

hashCode

public int hashCode()

Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that m1.equals(m2) implies that m1.hashCode()==m2.hashCode() for any two maps m1 and m2, as required by the general contract of Object#hashCode.

指定者:

hashCode 在接口中 Map<K,V>

覆盖:

hashCode 在类中 Object

返回:

the hash code value for this map

另请参阅:

Map.Entry.hashCode(), Object.equals(Object), Set.equals(Object)

toString

public String toString()

Returns a string representation of this map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("{}"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign ("=") followed by the associated value. Keys and values are converted to strings as by String#valueOf(Object).

覆盖:

toString 在类中 Object

返回:

a string representation of this map

clone

protected Object clone()
                throws CloneNotSupportedException

Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.

覆盖:

clone 在类中 Object

返回:

a shallow copy of this map

抛出:

CloneNotSupportedException - if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

另请参阅:

Cloneable