Java Reference
In-Depth Information
You can obtain a set of the keys in the map using the
keySet()
method, and a collection
of the values in the map using the
values()
method. The
entrySet()
method returns a set
of entries. The entries are instances of the
Map.Entry<K, V>
interface, where
Entry
is an
inner interface for the
Map
interface, as shown in Figure 21.5. Each entry in the set is a key/
value pair in the underlying map.
keySet()
values()
entrySet()
«interface»
java.util.Map.Entry<K,V>
+getKey(): K
+getValue(): V
+setValue(value: V): void
Returns the key from this entry.
Returns the value from this entry.
Replaces the value in this entry with a new value.
F
IGURE
21.5
The
Map.Entry
interface operates on an entry in the map.
The
AbstractMap
class is a convenience abstract class that implements all the methods in
the
Map
interface except the
entrySet()
method.
The
HashMap
,
LinkedHashMap
, and
TreeMap
classes are three
concrete implementations
of the
Map
interface, as shown in Figure 21.6.
AbstractMap
concrete implementations
«interface»
java.util.Map<K, V>
java.util.AbstractMap<K,V>
«interface»
java.util.SortedMap<K,V>
+
firstKey(): K
+
lastKey(): K
+
comparator(): Comparator<? super K>)
+
headMap(toKey: K): SortedMap<K,V>
+
tailMap(fromKey: K): SortedMap<K,V>
java.util.HashMap<K,V>
+HashMap()
+HashMap(initialCapacity: int,loadFactor: float)
+HashMap(m: Map<? extends K, ? extends V>)
java.util.LinkedHashMap<K,V>
+LinkedHashMap()
+LinkedHashMap(m: Map<? extends K,? extends V>)
+LinkedHashMap(initialCapacity: int,
loadFactor: float, accessOrder: boolean)
«interface»
java.util.NavigableMap<K, V>
+
floorKey(key: K): K
+
ceilingKey(key: K): K
+
lowerKey(key: K): K
+
higherKey(key: K): K
+
pollFirstEntry(): Map.EntrySet<K, V>
+
pollLastEntry(): Map.EntrySet<K, V>
java.util.TreeMap<K,V>
+TreeMap()
+TreeMap(m: Map<? extends K,? extends V>)
+TreeMap(c: Comparator<? super K>)
F
IGURE
21.6
The Java Collections Framework provides three concrete map classes.
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