java.lang.Object
- org.apache.flink.table.api.dataview.MapView<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

DataView
```
@PublicEvolving
public class MapView<K,V>
extends Object
implements DataView
```
A DataView that provides Map-like functionality in state entries.
A MapView can be backed by a Java HashMap or can leverage Flink's state backends depending on the context. In many unbounded data scenarios, the MapView delegates all calls to a MapState instead of the HashMap.
For aggregating functions, the view can be used as a field in the accumulator of an AggregateFunction or TableAggregateFunction when large amounts of data are expected. Aggregate functions might be used at various locations (pre-aggregation, combiners, merging of window slides, etc.) for some of these locations the data view is not backed by state but ArrayList.
For process table functions, the view can be used as a top-level state entry. Data views in PTFs are always backed by state.
Note: Keys of a MapView must not be null. Nulls in values are supported. For heap-based state backends, hashCode/equals of the original (i.e. external) class are used. However, the serialization format will use internal data structures.
The DataTypes of the view's keys and values are reflectively extracted from the accumulator definition. This includes the generic argument K and V of this class. If reflective extraction is not successful, it is possible to use a DataTypeHint on top the accumulator field. It will be mapped to the underlying collection.
The following examples show how to specify an AggregateFunction with a MapView:
```
{@code
 public class MyAccumulator {

   public MapView map = new MapView<>();

   // or explicit:
   // @DataTypeHint("MAP < STRING, INT >")
   // public MapView map = new MapView<>();

   public long count;
 }

 public class MyAggregateFunction extends AggregateFunction {
```

Constructor Summary

Constructors
Constructor Description

MapView()
Creates a map view.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`clear()`	Removes all entries of this map.
`boolean`	`contains(K key)`	Checks if the map view contains a value for a given key.
`Iterable<Map.Entry<K,V>>`	`entries()`	Returns all entries of the map view.
`boolean`	`equals(Object o)`
`V`	`get(K key)`	Return the value for the specified key or `null` if the key is not in the map view.
`Map<K,V>`	`getMap()`	Returns the entire view's content as an instance of `Map`.
`int`	`hashCode()`
`boolean`	`isEmpty()`	Returns true if the map view contains no key-value mappings, otherwise false.
`Iterator<Map.Entry<K,V>>`	`iterator()`	Returns an iterator over all entries of the map view.
`Iterable<K>`	`keys()`	Returns all the keys in the map view.
`static DataType`	`newMapViewDataType(DataType keyDataType, DataType valueDataType)`	Utility method for creating a `DataType` of `MapView` explicitly.
`void`	`put(K key, V value)`	Inserts a value for the given key into the map view.
`void`	`putAll(Map<K,V> map)`	Inserts all mappings from the specified map to this map view.
`void`	`remove(K key)`	Deletes the value for the given key.
`void`	`setMap(Map<K,V> map)`	Replaces the entire view's content with the content of the given `Map`.
`Iterable<V>`	`values()`	Returns all the values in the map view.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - MapView
```
public MapView()
```
    Creates a map view.
    The DataType of keys and values is reflectively extracted.
- Method Detail
  - getMap
```
public Map<K,V> getMap()
```
    Returns the entire view's content as an instance of Map.
  - setMap
```
public void setMap(Map<K,V> map)
```
    Replaces the entire view's content with the content of the given Map.
  - get
```
public V get(K key)
      throws Exception
```
    Return the value for the specified key or null if the key is not in the map view.
    
    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:
    
    Exception - Thrown if the system cannot get data.
  - put
```
public void put(K key,
                V value)
         throws Exception
```
    Inserts a value for the given key into the map view. If the map view already contains a value for the key, the existing value is overwritten.
    
    Parameters:
    
    key - The key for which the value is inserted.
    
    value - The value that is inserted for the key.
    
    Throws:
    
    Exception - Thrown if the system cannot put data.
  - putAll
```
public void putAll(Map<K,V> map)
            throws Exception
```
    Inserts all mappings from the specified map to this map view.
    
    Parameters:
    
    map - The map whose entries are inserted into this map view.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - remove
```
public void remove(K key)
            throws Exception
```
    Deletes the value for the given key.
    
    Parameters:
    
    key - The key for which the value is deleted.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - contains
```
public boolean contains(K key)
                 throws Exception
```
    Checks if the map view contains a value for a given key.
    
    Parameters:
    
    key - The key to check.
    
    Returns:
    
    True if there exists a value for the given key, false otherwise.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - entries
```
public Iterable<Map.Entry<K,V>> entries()
                                       throws Exception
```
    Returns all entries of the map view.
    
    Returns:
    
    An iterable of all the key-value pairs in the map view.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - keys
```
public Iterable<K> keys()
                 throws Exception
```
    Returns all the keys in the map view.
    
    Returns:
    
    An iterable of all the keys in the map.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - values
```
public Iterable<V> values()
                   throws Exception
```
    Returns all the values in the map view.
    
    Returns:
    
    An iterable of all the values in the map.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - iterator
```
public Iterator<Map.Entry<K,V>> iterator()
                                        throws Exception
```
    Returns an iterator over all entries of the map view.
    
    Returns:
    
    An iterator over all the mappings in the map.
    
    Throws:
    
    Exception - Thrown if the system cannot access the map.
  - isEmpty
```
public boolean isEmpty()
                throws Exception
```
    Returns true if the map view contains no key-value mappings, otherwise false.
    
    Returns:
    
    True if the map view contains no key-value mappings, otherwise false.
    
    Throws:
    
    Exception - Thrown if the system cannot access the state.
  - clear
```
public void clear()
```
    Removes all entries of this map.
    
    Specified by:
    
    clear in interface DataView
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object
  - newMapViewDataType
```
public static DataType newMapViewDataType(DataType keyDataType,
                                          DataType valueDataType)
```
    Utility method for creating a DataType of MapView explicitly.

Class MapView<K,​V>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

MapView

Method Detail

getMap

setMap

get

put

putAll

remove

contains

entries

keys

values

iterator

isEmpty

clear

equals

hashCode

newMapViewDataType

Class MapView<K,V>