AbstractMap (Java SE 10 & JDK 10 ) (original) (raw)
Constructor Detail
* #### AbstractMap
protected AbstractMap()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Method Detail
* #### 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`.
Specified by:
`[size](../../java/util/Map.html#size%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation returns `entrySet().size()`.
Returns:
the number of key-value mappings in this map
* #### isEmpty
public boolean isEmpty()
Returns `true` if this map contains no key-value mappings.
Specified by:
`[isEmpty](../../java/util/Map.html#isEmpty%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation returns `size() == 0`.
Returns:
`true` if this map contains no key-value mappings
* #### containsValue
public boolean containsValue([Object](../../java/lang/Object.html "class in java.lang") 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`Objects.equals(value, v)`. This operation will probably require time linear in the map size for most implementations of the `Map` interface.
Specified by:
`[containsValue](../../java/util/Map.html#containsValue%28java.lang.Object%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation iterates over `entrySet()` searching for an entry with the specified value. If such an entry is found,`true` is returned. If the iteration terminates without finding such an entry, `false` is returned. Note that this implementation requires linear time in the size of the map.
Parameters:
`value` \- value whose presence in this map is to be tested
Returns:
`true` if this map maps one or more keys to the specified value
Throws:
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the value is of an inappropriate type for this map ([optional](../../java/util/Collection.html#optional-restrictions))
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified value is null and this map does not permit null values ([optional](../../java/util/Collection.html#optional-restrictions))
* #### containsKey
public boolean containsKey([Object](../../java/lang/Object.html "class in java.lang") 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`Objects.equals(key, k)`. (There can be at most one such mapping.)
Specified by:
`[containsKey](../../java/util/Map.html#containsKey%28java.lang.Object%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation iterates over `entrySet()` searching for an entry with the specified key. If such an entry is found,`true` is returned. If the iteration terminates without finding such an entry, `false` is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.
Parameters:
`key` \- key whose presence in this map is to be tested
Returns:
`true` if this map contains a mapping for the specified key
Throws:
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the key is of an inappropriate type for this map ([optional](../../java/util/Collection.html#optional-restrictions))
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified key is null and this map does not permit null keys ([optional](../../java/util/Collection.html#optional-restrictions))
* #### get
public [V](../../java/util/AbstractMap.html "type parameter in AbstractMap") get([Object](../../java/lang/Object.html "class in java.lang") 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`Objects.equals(key, 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](../../java/util/Map.html#containsKey%28java.lang.Object%29) operation may be used to distinguish these two cases.
Specified by:
`[get](../../java/util/Map.html#get%28java.lang.Object%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation iterates over `entrySet()` searching for an entry with the specified key. If such an entry is found, the entry's value is returned. If the iteration terminates without finding such an entry, `null` is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.
Parameters:
`key` \- the key whose associated value is to be returned
Returns:
the value to which the specified key is mapped, or`null` if this map contains no mapping for the key
Throws:
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the key is of an inappropriate type for this map ([optional](../../java/util/Collection.html#optional-restrictions))
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified key is null and this map does not permit null keys ([optional](../../java/util/Collection.html#optional-restrictions))
* #### put
public [V](../../java/util/AbstractMap.html "type parameter in AbstractMap") put([K](../../java/util/AbstractMap.html "type parameter in AbstractMap") key,
[V](../../java/util/AbstractMap.html "type parameter in AbstractMap") 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)](../../java/util/Map.html#containsKey%28java.lang.Object%29) would return`true`.)
Specified by:
`[put](../../java/util/Map.html#put%28K,V%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation always throws an`UnsupportedOperationException`.
Parameters:
`key` \- key with which the specified value is to be associated
`value` \- value to be associated with the specified key
Returns:
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.)
Throws:
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the `put` operation is not supported by this map
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the class of the specified key or value prevents it from being stored in this map
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified key or value is null and this map does not permit null keys or values
`[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if some property of the specified key or value prevents it from being stored in this map
* #### remove
public [V](../../java/util/AbstractMap.html "type parameter in AbstractMap") remove([Object](../../java/lang/Object.html "class in java.lang") 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`Objects.equals(key, 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.
Specified by:
`[remove](../../java/util/Map.html#remove%28java.lang.Object%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation iterates over `entrySet()` searching for an entry with the specified key. If such an entry is found, its value is obtained with its `getValue` operation, the entry is removed from the collection (and the backing map) with the iterator's`remove` operation, and the saved value is returned. If the iteration terminates without finding such an entry, `null` is returned. Note that this implementation requires linear time in the size of the map; many implementations will override this method.
Note that this implementation throws an`UnsupportedOperationException` if the `entrySet` iterator does not support the `remove` method and this map contains a mapping for the specified key.
Parameters:
`key` \- key whose mapping is to be removed from the map
Returns:
the previous value associated with `key`, or`null` if there was no mapping for `key`.
Throws:
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the `remove` operation is not supported by this map
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the key is of an inappropriate type for this map ([optional](../../java/util/Collection.html#optional-restrictions))
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified key is null and this map does not permit null keys ([optional](../../java/util/Collection.html#optional-restrictions))
* #### putAll
public void putAll([Map](../../java/util/Map.html "interface in java.util")<? extends [K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),? extends [V](../../java/util/AbstractMap.html "type parameter in AbstractMap")> 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)](../../java/util/Map.html#put%28K,V%29) 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.
Specified by:
`[putAll](../../java/util/Map.html#putAll%28java.util.Map%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation iterates over the specified map's`entrySet()` collection, and calls this map's `put` operation once for each entry returned by the iteration.
Note that this implementation throws an`UnsupportedOperationException` if this map does not support the `put` operation and the specified map is nonempty.
Parameters:
`m` \- mappings to be stored in this map
Throws:
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the `putAll` operation is not supported by this map
`[ClassCastException](../../java/lang/ClassCastException.html "class in java.lang")` \- if the class of a key or value in the specified map prevents it from being stored in this map
`[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- 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](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- 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.
Specified by:
`[clear](../../java/util/Map.html#clear%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation calls `entrySet().clear()`.
Note that this implementation throws an`UnsupportedOperationException` if the `entrySet` does not support the `clear` operation.
Throws:
`[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the `clear` operation is not supported by this map
* #### keySet
public [Set](../../java/util/Set.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap")> keySet()
Returns a [Set](../../java/util/Set.html "interface in java.util") 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.
Specified by:
`[keySet](../../java/util/Map.html#keySet%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation returns a set that subclasses [AbstractSet](../../java/util/AbstractSet.html "class in java.util"). The subclass's iterator method returns a "wrapper object" over this map's `entrySet()` iterator. The `size` method delegates to this map's `size` method and the`contains` method delegates to this map's`containsKey` method.
The set is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same set.
Returns:
a set view of the keys contained in this map
* #### values
public [Collection](../../java/util/Collection.html "interface in java.util")<[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")> values()
Returns a [Collection](../../java/util/Collection.html "interface in java.util") 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.
Specified by:
`[values](../../java/util/Map.html#values%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Implementation Requirements:
This implementation returns a collection that subclasses [AbstractCollection](../../java/util/AbstractCollection.html "class in java.util"). The subclass's iterator method returns a "wrapper object" over this map's `entrySet()` iterator. The `size` method delegates to this map's `size` method and the `contains` method delegates to this map's`containsValue` method.
The collection is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same collection.
Returns:
a collection view of the values contained in this map
* #### equals
public boolean equals([Object](../../java/lang/Object.html "class in java.lang") 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.
Specified by:
`[equals](../../java/util/Map.html#equals%28java.lang.Object%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Overrides:
`[equals](../../java/lang/Object.html#equals%28java.lang.Object%29)` in class `[Object](../../java/lang/Object.html "class in java.lang")`
Implementation Requirements:
This implementation first checks if the specified object is this map; if so it returns `true`. Then, it checks if the specified object is a map whose size is identical to the size of this map; if not, it returns `false`. If so, it iterates over this map's`entrySet` collection, and checks that the specified map contains each mapping that this map contains. If the specified map fails to contain such a mapping, `false` is returned. If the iteration completes, `true` is returned.
Parameters:
`o` \- object to be compared for equality with this map
Returns:
`true` if the specified object is equal to this map
See Also:
[Object.hashCode()](../../java/lang/Object.html#hashCode%28%29), [HashMap](../../java/util/HashMap.html "class in java.util")
* #### 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()](../../java/lang/Object.html#hashCode%28%29).
Specified by:
`[hashCode](../../java/util/Map.html#hashCode%28%29)` in interface `[Map](../../java/util/Map.html "interface in java.util")<[K](../../java/util/AbstractMap.html "type parameter in AbstractMap"),[V](../../java/util/AbstractMap.html "type parameter in AbstractMap")>`
Overrides:
`[hashCode](../../java/lang/Object.html#hashCode%28%29)` in class `[Object](../../java/lang/Object.html "class in java.lang")`
Implementation Requirements:
This implementation iterates over `entrySet()`, calling[hashCode()](../../java/util/Map.Entry.html#hashCode%28%29) on each element (entry) in the set, and adding up the results.
Returns:
the hash code value for this map
See Also:
[Map.Entry.hashCode()](../../java/util/Map.Entry.html#hashCode%28%29), [Object.equals(Object)](../../java/lang/Object.html#equals%28java.lang.Object%29), [Set.equals(Object)](../../java/util/Set.html#equals%28java.lang.Object%29)
* #### toString
public [String](../../java/lang/String.html "class in java.lang") 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)](../../java/lang/String.html#valueOf%28java.lang.Object%29).
Overrides:
`[toString](../../java/lang/Object.html#toString%28%29)` in class `[Object](../../java/lang/Object.html "class in java.lang")`
Returns:
a string representation of this map
* #### clone
protected [Object](../../java/lang/Object.html "class in java.lang") clone()
throws [CloneNotSupportedException](../../java/lang/CloneNotSupportedException.html "class in java.lang")
Returns a shallow copy of this `AbstractMap` instance: the keys and values themselves are not cloned.
Overrides:
`[clone](../../java/lang/Object.html#clone%28%29)` in class `[Object](../../java/lang/Object.html "class in java.lang")`
Returns:
a shallow copy of this map
Throws:
`[CloneNotSupportedException](../../java/lang/CloneNotSupportedException.html "class in java.lang")` \- 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.
See Also:
[Cloneable](../../java/lang/Cloneable.html "interface in java.lang")