# HashMap

public class **HashMap** extends [AbstractMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html)\<K, V\>  
implements [Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<K, V\> [Cloneable](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Cloneable.html) [Serializable](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/Serializable.html)

|---|---|---|
| Known Direct Subclasses [LinkedHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/LinkedHashMap.html)\<K, V\> |---|---| | [LinkedHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/LinkedHashMap.html)\<K, V\> | Hash table and linked list implementation of the Map interface, with predictable iteration order. | |||

Hash table based implementation of the Map interface. This
implementation provides all of the optional map operations, and permits
null values and the null key. (The HashMap
class is roughly equivalent to Hashtable, except that it is
unsynchronized and permits nulls.) This class makes no guarantees as to
the order of the map; in particular, it does not guarantee that the order
will remain constant over time.

This implementation provides constant-time performance for the basic
operations (get and put), assuming the hash function
disperses the elements properly among the buckets. Iteration over
collection views requires time proportional to the "capacity" of the
HashMap instance (the number of buckets) plus its size (the number
of key-value mappings). Thus, it's very important not to set the initial
capacity too high (or the load factor too low) if iteration performance is
important.

An instance of HashMap has two parameters that affect its
performance: *initial capacity* and *load factor*. The
*capacity* is the number of buckets in the hash table, and the initial
capacity is simply the capacity at the time the hash table is created. The
*load factor* is a measure of how full the hash table is allowed to
get before its capacity is automatically increased. When the number of
entries in the hash table exceeds the product of the load factor and the
current capacity, the hash table is *rehashed* (that is, internal data
structures are rebuilt) so that the hash table has approximately twice the
number of buckets.

As a general rule, the default load factor (.75) offers a good
tradeoff between time and space costs. Higher values decrease the
space overhead but increase the lookup cost (reflected in most of
the operations of the HashMap class, including
get and put). The expected number of entries in
the map and its load factor should be taken into account when
setting its initial capacity, so as to minimize the number of
rehash operations. If the initial capacity is greater than the
maximum number of entries divided by the load factor, no rehash
operations will ever occur.

If many mappings are to be stored in a HashMap
instance, creating it with a sufficiently large capacity will allow
the mappings to be stored more efficiently than letting it perform
automatic rehashing as needed to grow the table. Note that using
many keys with the same `hashCode()` is a sure way to slow
down performance of any hash table. To ameliorate impact, when keys
are `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Comparable.html`, this class may use comparison order among
keys to help break ties.

**Note that this implementation is not synchronized.**
If multiple threads access a hash map concurrently, and at least one of
the threads modifies the map structurally, it *must* be
synchronized externally. (A structural modification is any operation
that adds or deletes one or more mappings; merely changing the value
associated with a key that an instance already contains is not a
structural modification.) This is typically accomplished by
synchronizing on some object that naturally encapsulates the map.

If no such object exists, the map should be "wrapped" using the
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collections.html#synchronizedMap(java.util.Map<K,%20V>)`
method. This is best done at creation time, to prevent accidental
unsynchronized access to the map:

```
   Map m = Collections.synchronizedMap(new HashMap(...));
```

The iterators returned by all of this class's "collection view methods"
are *fail-fast*: if the map is structurally modified at any time after
the iterator is created, in any way except through the iterator's own
remove method, the iterator will throw a
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/ConcurrentModificationException.html`. Thus, in the face of concurrent
modification, the iterator fails quickly and cleanly, rather than risking
arbitrary, non-deterministic behavior at an undetermined time in the
future.

Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: *the fail-fast behavior of iterators should be used only to detect bugs.*

This class is a member of the
[Java Collections Framework](https://developers.google.com/j2objc/javadoc/jre/openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html).

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode()`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/TreeMap.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Hashtable.html`

### Public Constructor Summary

|---|---|
|   | [HashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#HashMap(int,%20float))(int initialCapacity, float loadFactor) Constructs an empty HashMap with the specified initial capacity and load factor. |
|   | [HashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#HashMap(int))(int initialCapacity) Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75). |
|   | [HashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#HashMap())() Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75). |
|   | [HashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#HashMap(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Constructs a new HashMap with the same mappings as the specified Map. |

### Public Method Summary

|---|---|
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#clear())() Removes all of the mappings from this map. |
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#clone())() Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned. |
| V | [compute](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#compute(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping). |
| V | [computeIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#computeIfAbsent(K,%20java.util.function.Function<?%20super%20K,%20?%20extends%20V>))(K key, [Function](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Function.html)\<? super K, ? extends V\> mappingFunction) If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`. |
| V | [computeIfPresent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#computeIfPresent(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value. |
| boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns true if this map contains a mapping for the specified key. |
| boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns true if this map maps one or more keys to the specified value. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| void | [forEach](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#forEach(java.util.function.BiConsumer<?%20super%20K,%20?%20super%20V>))([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
| V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| V | [getOrDefault](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#getOrDefault(java.lang.Object,%20V))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, V defaultValue) Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#isEmpty())() Returns true if this map contains no key-value mappings. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [merge](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#merge(K,%20V,%20java.util.function.BiFunction<?%20super%20V,%20?%20super%20V,%20?%20extends%20V>))(K key, V value, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super V, ? super V, ? extends V\> remappingFunction) If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value. |
| V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map. |
| void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map. |
| V | [putIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#putIfAbsent(K,%20V))(K key, V value) If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value. |
| boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#remove(java.lang.Object,%20java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Removes the entry for the specified key only if it is currently mapped to the specified value. |
| V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for the specified key from this map if present. |
| boolean | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#replace(K,%20V,%20V))(K key, V oldValue, V newValue) Replaces the entry for the specified key only if currently mapped to the specified value. |
| V | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#replace(K,%20V))(K key, V value) Replaces the entry for the specified key only if it is currently mapped to some value. |
| void | [replaceAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#replaceAll(java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
| int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#size())() Returns the number of key-value mappings in this map. |
| [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

### Inherited Method Summary

From class [java.util.AbstractMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html)

|---|---|
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#clear())() Removes all of the mappings from this map (optional operation). |
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#clone())() Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned. |
| boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns `true` if this map contains a mapping for the specified key. |
| boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns `true` if this map maps one or more keys to the specified value. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this map for equality. |
| V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#hashCode())() Returns the hash code value for this map. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#isEmpty())() Returns `true` if this map contains no key-value mappings. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map (optional operation). |
| void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map (optional operation). |
| V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for a key from this map if it is present (optional operation). |
| int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#size())() Returns the number of key-value mappings in this map. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#toString())() Returns a string representation of this map. |
| [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notify())() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| final void | [notifyAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notifyAll())() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

From interface [java.util.Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)

|---|---|
| abstract void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#clear())() Removes all of the mappings from this map (optional operation). |
| V | [compute](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#compute(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping). |
| V | [computeIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#computeIfAbsent(K,%20java.util.function.Function<?%20super%20K,%20?%20extends%20V>))(K key, [Function](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Function.html)\<? super K, ? extends V\> mappingFunction) If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`. |
| V | [computeIfPresent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#computeIfPresent(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value. |
| abstract boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns `true` if this map contains a mapping for the specified key. |
| abstract boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns `true` if this map maps one or more keys to the specified value. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| abstract boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this map for equality. |
| void | [forEach](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#forEach(java.util.function.BiConsumer<?%20super%20K,%20?%20super%20V>))([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
| abstract V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| V | [getOrDefault](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#getOrDefault(java.lang.Object,%20V))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, V defaultValue) Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key. |
| abstract int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#hashCode())() Returns the hash code value for this map. |
| abstract boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#isEmpty())() Returns `true` if this map contains no key-value mappings. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [merge](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#merge(K,%20V,%20java.util.function.BiFunction<?%20super%20V,%20?%20super%20V,%20?%20extends%20V>))(K key, V value, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super V, ? super V, ? extends V\> remappingFunction) If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value. |
| abstract V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map (optional operation). |
| abstract void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map (optional operation). |
| V | [putIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#putIfAbsent(K,%20V))(K key, V value) If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value. |
| boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#remove(java.lang.Object,%20java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Removes the entry for the specified key only if it is currently mapped to the specified value. |
| abstract V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for a key from this map if it is present (optional operation). |
| boolean | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replace(K,%20V,%20V))(K key, V oldValue, V newValue) Replaces the entry for the specified key only if currently mapped to the specified value. |
| V | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replace(K,%20V))(K key, V value) Replaces the entry for the specified key only if it is currently mapped to some value. |
| void | [replaceAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replaceAll(java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
| abstract int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#size())() Returns the number of key-value mappings in this map. |
| abstract [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

## Public Constructors

#### public
**HashMap**
(int initialCapacity, float loadFactor)

Constructs an empty HashMap with the specified initial
capacity and load factor.

##### Parameters

| initialCapacity | the initial capacity |
| loadFactor | the load factor |
|---|---|

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the initial capacity is negative or the load factor is nonpositive |
|---|---|

#### public
**HashMap**
(int initialCapacity)

Constructs an empty HashMap with the specified initial
capacity and the default load factor (0.75).

##### Parameters

| initialCapacity | the initial capacity. |
|---|---|

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the initial capacity is negative. |
|---|---|

#### public
**HashMap**
()

Constructs an empty HashMap with the default initial capacity
(16) and the default load factor (0.75).

#### public
**HashMap**
([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m)

Constructs a new HashMap with the same mappings as the
specified Map. The HashMap is created with
default load factor (0.75) and an initial capacity sufficient to
hold the mappings in the specified Map.

##### Parameters

| m | the map whose mappings are to be placed in this map |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified map is null |
|---|---|

## Public Methods

#### public void
**clear**
()

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

#### public [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)
**clone**
()

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

##### Returns

- a shallow copy of this map

#### public V
**compute**
(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction)

Attempts to compute a mapping for the specified key and its current
mapped value (or `null` if there is no current mapping). For
example, to either create or append a `String` msg to a value
mapping:

     map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))

(Method `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#merge(K,%20V,%20java.util.function.BiFunction<?%20super%20V,%20?%20super%20V,%20?%20extends%20V>)` is often simpler to use for such purposes.)

If the remapping function returns `null`, the mapping is removed
(or remains absent if initially absent). If the remapping function
itself throws an (unchecked) exception, the exception is rethrown, and
the current mapping is left unchanged.

The remapping function should not modify this map during computation.

##### Parameters

| key | key with which the specified value is to be associated |
| remappingFunction | the remapping function to compute a value |
|---|---|

##### Returns

- the new value associated with the specified key, or null if none

#### public V
**computeIfAbsent**
(K key, [Function](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Function.html)\<? super K, ? extends V\> mappingFunction)

If the specified key is not already associated with a value (or is mapped
to `null`), attempts to compute its value using the given mapping
function and enters it into this map unless `null`.

If the mapping function returns `null`, no mapping is recorded.
If the mapping function itself throws an (unchecked) exception, the
exception is rethrown, and no mapping is recorded. The most
common usage is to construct a new object serving as an initial
mapped value or memoized result, as in:

     map.computeIfAbsent(key, k -> new Value(f(k)));
     
Or to implement a multi-value map, `Map<K,Collection<V>>`,
supporting multiple values per key:

     map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
     
The mapping function should not modify this map during computation.

##### Parameters

| key | key with which the specified value is to be associated |
| mappingFunction | the mapping function to compute a value |
|---|---|

##### Returns

- the current (existing or computed) value associated with the specified key, or null if the computed value is null

#### public V
**computeIfPresent**
(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction)

If the value for the specified key is present and non-null, attempts to
compute a new mapping given the key and its current mapped value.

If the remapping function returns `null`, the mapping is removed.
If the remapping function itself throws an (unchecked) exception, the
exception is rethrown, and the current mapping is left unchanged.

The remapping function should not modify this map during computation.

##### Parameters

| key | key with which the specified value is to be associated |
| remappingFunction | the remapping function to compute a value |
|---|---|

##### Returns

- the new value associated with the specified key, or null if none

#### public boolean
**containsKey**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key)

Returns true if this map contains a mapping for the
specified key.

##### Parameters

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

##### Returns

- true if this map contains a mapping for the specified key.

#### public boolean
**containsValue**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value)

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

##### 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

#### public [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\>
**entrySet**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` 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.

##### Returns

- a set view of the mappings contained in this map

#### public void
**forEach**
([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action)

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

##### Parameters

| action | The action to be performed for each entry |
|---|---|

#### public V
**get**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) 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.)

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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#containsKey(java.lang.Object)` operation may be used to
distinguish these two cases.

##### 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

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html#put(K,%20V)`

#### public V
**getOrDefault**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, V defaultValue)

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

##### Parameters

| key | the key whose associated value is to be returned |
| defaultValue | the default mapping of the key |
|---|---|

##### Returns

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

#### public boolean
**isEmpty**
()

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

##### Returns

- true if this map contains no key-value mappings

#### public [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\>
**keySet**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` 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.

##### Returns

- a set view of the keys contained in this map

#### public V
**merge**
(K key, V value, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super V, ? super V, ? extends V\> remappingFunction)

If the specified key is not already associated with a value or is
associated with null, associates it with the given non-null value.
Otherwise, replaces the associated value with the results of the given
remapping function, or removes if the result is `null`. This
method may be of use when combining multiple mapped values for a key.
For example, to either create or append a `String msg` to a
value mapping:

     map.merge(key, msg, String::concat)
     
If the remapping function returns `null`, the mapping is removed.
If the remapping function itself throws an (unchecked) exception, the
exception is rethrown, and the current mapping is left unchanged.

The remapping function should not modify this map during computation.

##### Parameters

| key | key with which the resulting value is to be associated |
| value | the non-null value to be merged with the existing value associated with the key or, if no existing value or a null value is associated with the key, to be associated with the key |
| remappingFunction | the remapping function to recompute a value if present |
|---|---|

##### Returns

- the new value associated with the specified key, or null if no value is associated with the key

#### public V
**put**
(K key, V value)

Associates the specified value with the specified key in this map.
If the map previously contained a mapping for the key, the old
value is replaced.

##### 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.)

#### public void
**putAll**
([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m)

Copies all of the mappings from the specified map to this map.
These mappings will replace any mappings that this map had for
any of the keys currently in the specified map.

##### Parameters

| m | mappings to be stored in this map |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified map is null |
|---|---|

#### public V
**putIfAbsent**
(K key, V value)

If the specified key is not already associated with a value (or is mapped
to `null`) associates it with the given value and returns
`null`, else returns the current value.

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

#### public boolean
**remove**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value)

Removes the entry for the specified key only if it is currently
mapped to the specified value.

##### Parameters

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

##### Returns

- `true` if the value was removed

#### public V
**remove**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key)

Removes the mapping for the specified key from this map if present.

##### 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. (A null return can also indicate that the map previously associated null with key.)

#### public boolean
**replace**
(K key, V oldValue, V newValue)

Replaces the entry for the specified key only if currently
mapped to the specified value.

##### Parameters

| key | key with which the specified value is associated |
| oldValue | value expected to be associated with the specified key |
| newValue | value to be associated with the specified key |
|---|---|

##### Returns

- `true` if the value was replaced

#### public V
**replace**
(K key, V value)

Replaces the entry for the specified key only if it is
currently mapped to some value.

##### Parameters

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

##### Returns

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

#### public void
**replaceAll**
([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function)

Replaces each entry's value with the result of invoking the given
function on that entry until all entries have been processed or the
function throws an exception. Exceptions thrown by the function are
relayed to the caller.

##### Parameters

| function | the function to apply to each entry |
|---|---|

#### public int
**size**
()

Returns the number of key-value mappings in this map.

##### Returns

- the number of key-value mappings in this map

#### public [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\>
**values**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` 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.

##### Returns

- a view of the values contained in this map