AbstractMap
abstract class AbstractMap<K : Any!, V : Any!> : MutableMap<K, V>
| kotlin.Any | |
| ↳ | java.util.AbstractMap |
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.
Summary
| Nested classes | |
|---|---|
| open |
An Entry maintaining a key and a value. |
| open |
An unmodifiable Entry maintaining a key and a value. |
| Protected constructors | |
|---|---|
|
Sole constructor. |
|
| Public methods | |
|---|---|
| open Unit |
clear()Removes all of the mappings from this map (optional operation). |
| open Boolean |
containsKey(key: K?)Returns |
| open Boolean |
containsValue(value: V?)Returns |
| open Boolean |
Compares the specified object with this map for equality. |
| open V? |
get(key: K?)Returns the value to which the specified key is mapped, or |
| open Int |
hashCode()Returns the hash code value for this map. |
| open Boolean |
isEmpty()Returns |
| open V? |
put(key: K, value: V)Associates the specified value with the specified key in this map (optional operation). |
| open Unit |
Copies all of the mappings from the specified map to this map (optional operation). |
| open V? |
remove(key: K?)Removes the mapping for a key from this map if it is present (optional operation). |
| open String |
toString()Returns a string representation of this map. |
| Protected methods | |
|---|---|
| open Any |
clone()Returns a shallow copy of this |
| Properties | |
|---|---|
| abstract MutableSet<MutableEntry<K, V>> | |
| open MutableSet<K> |
Returns a |
| open Int |
Returns the number of key-value mappings in this map. |
| open MutableCollection<V> |
Returns a |
Protected constructors
AbstractMap
protected AbstractMap()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Public methods
clear
open fun clear(): Unit
Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.
| Exceptions | |
|---|---|
java.lang.UnsupportedOperationException |
if the clear operation is not supported by this map |
containsKey
open fun containsKey(key: K?): Boolean
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.)
| Parameters | |
|---|---|
key |
K?: key whose presence in this map is to be tested |
| Return | |
|---|---|
Boolean |
true if this map contains a mapping for the specified key |
| Exceptions | |
|---|---|
java.lang.ClassCastException |
if the key is of an inappropriate type for this map (java.util.Collection#) |
java.lang.NullPointerException |
if the specified key is null and this map does not permit null keys (java.util.Collection#) |
containsValue
open fun containsValue(value: V?): Boolean
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.
| Parameters | |
|---|---|
value |
V?: value whose presence in this map is to be tested |
| Return | |
|---|---|
Boolean |
true if this map maps one or more keys to the specified value |
| Exceptions | |
|---|---|
java.lang.ClassCastException |
if the value is of an inappropriate type for this map (java.util.Collection#) |
java.lang.NullPointerException |
if the specified value is null and this map does not permit null values (java.util.Collection#) |
equals
open fun equals(other: Any?): Boolean
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.
| Parameters | |
|---|---|
obj |
the reference object with which to compare. |
o |
object to be compared for equality with this map |
| Return | |
|---|---|
Boolean |
true if the specified object is equal to this map |
get
open fun get(key: K?): V?
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 operation may be used to distinguish these two cases.
| Parameters | |
|---|---|
key |
K?: the key whose associated value is to be returned |
| Return | |
|---|---|
V? |
the value to which the specified key is mapped, or null if this map contains no mapping for the key |
| Exceptions | |
|---|---|
java.lang.ClassCastException |
if the key is of an inappropriate type for this map (java.util.Collection#) |
java.lang.NullPointerException |
if the specified key is null and this map does not permit null keys (java.util.Collection#) |
hashCode
open fun hashCode(): Int
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.
| Return | |
|---|---|
Int |
the hash code value for this map |
isEmpty
open fun isEmpty(): Boolean
Returns true if this map contains no key-value mappings.
| Return | |
|---|---|
Boolean |
true if this map contains no key-value mappings |
put
open fun put(
key: K,
value: V
): V?
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.)
| Parameters | |
|---|---|
key |
K: key with which the specified value is to be associated |
value |
V: value to be associated with the specified key |
| Return | |
|---|---|
V? |
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.) |
| Exceptions | |
|---|---|
java.lang.UnsupportedOperationException |
if the put operation is not supported by this map |
java.lang.ClassCastException |
if the class of the specified key or value prevents it from being stored in this map |
java.lang.NullPointerException |
if the specified key or value is null and this map does not permit null keys or values |
java.lang.IllegalArgumentException |
if some property of the specified key or value prevents it from being stored in this map |
putAll
open fun putAll(from: Map<out K, V>): Unit
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. If the specified map has a defined encounter order, processing of its mappings generally occurs in that order.
| Parameters | |
|---|---|
m |
mappings to be stored in this map |
| Exceptions | |
|---|---|
java.lang.UnsupportedOperationException |
if the putAll operation is not supported by this map |
java.lang.ClassCastException |
if the class of a key or value in the specified map prevents it from being stored in this map |
java.lang.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 |
java.lang.IllegalArgumentException |
if some property of a key or value in the specified map prevents it from being stored in this map |
remove
open fun remove(key: K?): V?
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.
| Parameters | |
|---|---|
key |
K?: key whose mapping is to be removed from the map |
| Return | |
|---|---|
V? |
the previous value associated with key, or null if there was no mapping for key. |
| Exceptions | |
|---|---|
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this map |
java.lang.ClassCastException |
if the key is of an inappropriate type for this map (java.util.Collection#) |
java.lang.NullPointerException |
if the specified key is null and this map does not permit null keys (java.util.Collection#) |
toString
open fun toString(): String
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).
| Return | |
|---|---|
String |
a string representation of this map |
Protected methods
clone
protected open fun clone(): Any
Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned.
| Return | |
|---|---|
Any |
a shallow copy of this map |
| Exceptions | |
|---|---|
java.lang.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. |
Properties
entries
abstract val entries: MutableSet<MutableEntry<K, V>>
| Return | |
|---|---|
MutableSet<MutableEntry<K, V>> |
a set view of the mappings contained in this map |
keys
open val keys: MutableSet<K>
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.
| Return | |
|---|---|
MutableSet<K> |
a set view of the keys contained in this map |
size
open val size: Int
Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
| Return | |
|---|---|
Int |
the number of key-value mappings in this map |
values
open val values: MutableCollection<V>
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.
| Return | |
|---|---|
MutableCollection<V> |
a collection view of the values contained in this map |