- Type Parameters:
- K- the type of keys maintained by this map
- V- the type of mapped values
- All Superinterfaces:
- Map<K,- V> 
- All Known Subinterfaces:
- ConcurrentNavigableMap<K,,- V> - NavigableMap<K,,- V> - SortedMap<K,- V> 
- All Known Implementing Classes:
- ConcurrentSkipListMap,- LinkedHashMap,- TreeMap
SequencedMap is similar to that of the elements of a SequencedCollection,
 but the ordering applies to mappings instead of individual elements.
 
 The bulk operations on this map, including the forEach and the
 replaceAll methods, operate on this map's mappings in
 encounter order.
 
 The view collections provided by the
 keySet,
 values,
 entrySet,
 sequencedKeySet,
 sequencedValues,
 and
 sequencedEntrySet methods all reflect the encounter order
 of this map. Even though the return values of the keySet, values, and
 entrySet methods are not sequenced types, the elements
 in those view collections do reflect the encounter order of this map. Thus, the
 iterators returned by the statements
 
    var it1 = sequencedMap.entrySet().iterator();
    var it2 = sequencedMap.sequencedEntrySet().iterator();
sequencedMap in that map's encounter order.
 This interface provides methods to add mappings, to retrieve mappings, and to remove mappings at either end of the map's encounter order.
 This interface also defines the reversed() method, which provides a
 reverse-ordered view of this map.
 In the reverse-ordered view, the concepts of first and last are inverted, as
 are the concepts of successor and predecessor. The first mapping of this map
 is the last mapping of the reverse-ordered view, and vice-versa. The successor of some
 mapping in this map is its predecessor in the reversed view, and vice-versa. All
 methods that respect the encounter order of the map operate as if the encounter order
 is inverted. For instance, the forEach method of the reversed view reports
 the mappings in order from the last mapping of this map to the first. In addition, all of
 the view collections of the reversed view also reflect the inverse of this map's
 encounter order. For example,
 
    var itr = sequencedMap.reversed().entrySet().iterator();
reversed method,
 and its impact on the ordering semantics of all applicable methods and views, allow convenient
 iteration, searching, copying, and streaming of this map's mappings in either forward order or
 reverse order.
 A map's reverse-ordered view is generally not serializable, even if the original map is serializable.
 The Map.Entry instances obtained by iterating the Map.entrySet() view, the
 sequencedEntrySet() view, and its reverse-ordered view, maintain a connection to the
 underlying map. This connection is guaranteed only during the iteration. It is unspecified
 whether the connection is maintained outside of the iteration. If the underlying map permits
 it, calling an Entry's setValue method will modify the value of the
 underlying mapping. It is, however, unspecified whether modifications to the value in the
 underlying mapping are visible in the Entry instance.
 
 The methods
 firstEntry(),
 lastEntry(),
 pollFirstEntry(), and
 pollLastEntry()
 return Map.Entry instances that represent snapshots of mappings as
 of the time of the call. They do not support mutation of the
 underlying map via the optional setValue method.
 
 Depending upon the implementation, the Entry instances returned by other
 means might or might not be connected to the underlying map. For example, consider
 an Entry obtained in the following manner:
 
    var entry = sequencedMap.sequencedEntrySet().getFirst();
setValue method of the
 Entry thus obtained will update a mapping in the underlying map, or whether
 it will throw an exception, or whether changes to the underlying map are visible in
 that Entry.
 
 This interface has the same requirements on the equals and hashCode
 methods as defined by Map.equals and Map.hashCode.
 Thus, a Map and a SequencedMap will compare equals if and only
 if they have equal mappings, irrespective of ordering.
 
This class is a member of the Java Collections Framework.
- Since:
- 21
- 
Nested Class Summary
- 
Method SummaryModifier and TypeMethodDescriptionReturns the first key-value mapping in this map, ornullif the map is empty.Returns the last key-value mapping in this map, ornullif the map is empty.Removes and returns the first key-value mapping in this map, ornullif the map is empty (optional operation).Removes and returns the last key-value mapping in this map, ornullif the map is empty (optional operation).default VInserts the given mapping into the map if it is not already present, or replaces the value of a mapping if it is already present (optional operation).default VInserts the given mapping into the map if it is not already present, or replaces the value of a mapping if it is already present (optional operation).reversed()Returns a reverse-ordered view of this map.default SequencedSet<Map.Entry<K, V>> Returns aSequencedSetview of this map'sentrySet.default SequencedSet<K> Returns aSequencedSetview of this map'skeySet.default SequencedCollection<V> Returns aSequencedCollectionview of this map'svaluescollection.Methods declared in interface java.util.Mapclear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, get, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values
- 
Method Details- 
reversedSequencedMap<K,V> reversed()Returns a reverse-ordered view of this map. The encounter order of mappings in the returned view is the inverse of the encounter order of mappings in this map. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the implementation permits modifications to this view, the modifications "write through" to the underlying map. Changes to the underlying map might or might not be visible in this reversed view, depending upon the implementation.- Returns:
- a reverse-ordered view of this map
 
- 
firstEntryReturns the first key-value mapping in this map, ornullif the map is empty.- Implementation Requirements:
- The implementation in this interface obtains the iterator of this map's entrySet. If the iterator has an element, it returns an unmodifiable copy of that element. Otherwise, it returns null.
- Returns:
- the first key-value mapping,
         or nullif this map is empty
 
- 
lastEntryReturns the last key-value mapping in this map, ornullif the map is empty.- Implementation Requirements:
- The implementation in this interface obtains the iterator of the entrySet of this map's reversed view. If the iterator has an element, it returns an unmodifiable copy of that element. Otherwise, it returns null.
- Returns:
- the last key-value mapping,
         or nullif this map is empty
 
- 
pollFirstEntryRemoves and returns the first key-value mapping in this map, ornullif the map is empty (optional operation).- Implementation Requirements:
- The implementation in this interface obtains the iterator of this map's entrySet.
 If the iterator has an element, it calls removeon the iterator and then returns an unmodifiable copy of that element. Otherwise, it returns null.
- Returns:
- the removed first entry of this map,
         or nullif this map is empty
- Throws:
- UnsupportedOperationException- if this collection implementation does not support this operation
 
- 
pollLastEntryRemoves and returns the last key-value mapping in this map, ornullif the map is empty (optional operation).- Implementation Requirements:
- The implementation in this interface obtains the iterator of the entrySet of this map's
 reversed view. If the iterator has an element, it calls removeon the iterator and then returns an unmodifiable copy of that element. Otherwise, it returns null.
- Returns:
- the removed last entry of this map,
         or nullif this map is empty
- Throws:
- UnsupportedOperationException- if this collection implementation does not support this operation
 
- 
putFirstInserts the given mapping into the map if it is not already present, or replaces the value of a mapping if it is already present (optional operation). After this operation completes normally, the given mapping will be present in this map, and it will be the first mapping in this map's encounter order.- Implementation Requirements:
- The implementation in this interface always throws
 UnsupportedOperationException.
- Parameters:
- k- the key
- v- the value
- Returns:
- the value previously associated with k, or null if none
- Throws:
- UnsupportedOperationException- if this collection implementation does not support this operation
 
- 
putLastInserts the given mapping into the map if it is not already present, or replaces the value of a mapping if it is already present (optional operation). After this operation completes normally, the given mapping will be present in this map, and it will be the last mapping in this map's encounter order.- Implementation Requirements:
- The implementation in this interface always throws
 UnsupportedOperationException.
- Parameters:
- k- the key
- v- the value
- Returns:
- the value previously associated with k, or null if none
- Throws:
- UnsupportedOperationException- if this collection implementation does not support this operation
 
- 
sequencedKeySetReturns aSequencedSetview of this map'skeySet.- Implementation Requirements:
- The implementation in this interface returns a SequencedSetinstance that behaves as follows. ItsaddandaddAllmethods throwUnsupportedOperationException. Itsreversedmethod returns thesequencedKeySetview of thereversedview of this map. Each of its other methods calls the corresponding method of thekeySetview of this map.
- Returns:
- a SequencedSetview of this map'skeySet
 
- 
sequencedValuesReturns aSequencedCollectionview of this map'svaluescollection.- Implementation Requirements:
- The implementation in this interface returns a SequencedCollectioninstance that behaves as follows. ItsaddandaddAllmethods throwUnsupportedOperationException. Itsreversedmethod returns thesequencedValuesview of thereversedview of this map. ItsequalsandhashCodemethods are inherited fromObject. Each of its other methods calls the corresponding method of thevaluesview of this map.
- Returns:
- a SequencedCollectionview of this map'svaluescollection
 
- 
sequencedEntrySetReturns aSequencedSetview of this map'sentrySet.- Implementation Requirements:
- The implementation in this interface returns a SequencedSetinstance that behaves as follows. ItsaddandaddAllmethods throwUnsupportedOperationException. Itsreversedmethod returns thesequencedEntrySetview of thereversedview of this map. Each of its other methods calls the corresponding method of theentrySetview of this map.
- Returns:
- a SequencedSetview of this map'sentrySet
 
 
-