V tej vadnici bomo s pomočjo primerov spoznali razred Java EnumMap in njegovo delovanje.
EnumMap
Razred okviru Java zbirk zagotavlja izvajanje karto za elemente z ENUM.
Leta EnumMap
so ENUM elementi uporabljajo kot ključi . Izvaja vmesnik Map.
Preden se naučimo EnumMap
, se prepričajte, da ste vedeli o Java Enumih.
Ustvarjanje EnumMap
Če želite ustvariti zemljevid naštevanja, moramo najprej uvoziti java.util.EnumMap
paket. Ko uvozimo paket, tukaj je opisano, kako lahko v Javi ustvarimo zemljevide enum.
enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) EnumMap sizes = new EnumMap(Size.class);
V zgornjem primeru smo ustvarili enum map z imenom velikosti.
Tukaj,
- Velikost - tipke enum, ki preslikajo na vrednosti
- Celo število - vrednosti mape oštevilčenja, povezane z ustreznimi ključi
Metode EnumMap
EnumMap
Razred določa metode, ki nam omogočajo, da opravljajo različne elemente o ENUM zemljevidih.
Vstavite elemente v EnumMap
put()
- vstavi določeno preslikavo ključ / vrednost (vnos) na zemljevid naštevanjaputAll()
- na to zemljevid vstavi vse vnose določenega zemljevida
Na primer
import java.util.EnumMap; class Main ( enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) public static void main(String() args) ( // Creating an EnumMap of the Size enum EnumMap sizes1 = new EnumMap(Size.class); // Using the put() Method sizes1.put(Size.SMALL, 28); sizes1.put(Size.MEDIUM, 32); System.out.println("EnumMap1: " + sizes1); EnumMap sizes2 = new EnumMap(Size.class); // Using the putAll() Method sizes2.putAll(sizes1); sizes2.put(Size.LARGE, 36); System.out.println("EnumMap2: " + sizes2); ) )
Izhod
EnumMap1: (SMALL = 28, MEDIUM = 32) EnumMap2: (SMALL = 28, MEDIUM = 32, LARGE = 36)
V zgornjem primeru smo uporabili putAll()
metodo za vstavljanje vseh elementov enum map velikosti1 v enum map velikosti2.
Prav tako je mogoče na enum map vstaviti elemente z drugih zemljevidov, kot HashMap
so TreeMap
, itd putAll()
. Vendar bi morali biti vsi zemljevidi istega števila.
Dostopite do elementov EnumMap
1. Uporaba entrySet (), keySet () in vrednosti ()
entrySet()
- vrne nabor vseh preslikav ključev / vrednosti (vnos) zemljevida oštevilčenjakeySet()
- vrne nabor vseh ključev zemljevida za naštevanjevalues()
- vrne niz vseh vrednosti enum map
Na primer
import java.util.EnumMap; class Main ( enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) public static void main(String() args) ( // Creating an EnumMap of the Size enum EnumMap sizes = new EnumMap(Size.class); sizes.put(Size.SMALL, 28); sizes.put(Size.MEDIUM, 32); sizes.put(Size.LARGE, 36); sizes.put(Size.EXTRALARGE, 40); System.out.println("EnumMap: " + sizes); // Using the entrySet() Method System.out.println("Key/Value mappings: " + sizes.entrySet()); // Using the keySet() Method System.out.println("Keys: " + sizes.keySet()); // Using the values() Method System.out.println("Values: " + sizes.values()); ) )
Izhod
EnumMap: (SMALL = 28, SREDNJI = 32, LARGE = 36, EXTRALARGE = 40) Preslikave ključa / vrednosti: (SMALL = 28, SREDNJE = 32, LARGE = 36, EXTRALARGE = 40) Tipke: (SMALL, SREDNJE, LARGE, EXTRALARGE) Vrednosti: (28, 32, 36, 40)
2. Uporaba metode get ()
get()
Metoda vrne vrednost, povezano z določeno tipko. Vrne se, null
če določenega ključa ni mogoče najti.
Na primer
import java.util.EnumMap; class Main ( enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) public static void main(String() args) ( // Creating an EnumMap of the Size enum EnumMap sizes = new EnumMap(Size.class); sizes.put(Size.SMALL, 28); sizes.put(Size.MEDIUM, 32); sizes.put(Size.LARGE, 36); sizes.put(Size.EXTRALARGE, 40); System.out.println("EnumMap: " + sizes); // Using the get() Method int value = sizes.get(Size.MEDIUM); System.out.println("Value of MEDIUM: " + value); ) )
Izhod
EnumMap: (SMALL = 28, SREDNJA = 32, LARGE = 36, EXTRALARGE = 40) Vrednost MEDIUM: 32
Odstranite elemente EnumMap
remove(key)
- vrne in z zemljevida odstrani vnos, povezan z določenim ključemremove(key, value)
- odstrani vnos s zemljevida samo, če je podan ključ preslikan na določeno vrednost in vrne logično vrednost
Na primer
import java.util.EnumMap; class Main ( enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) public static void main(String() args) ( // Creating an EnumMap of the Size enum EnumMap sizes = new EnumMap(Size.class); sizes.put(Size.SMALL, 28); sizes.put(Size.MEDIUM, 32); sizes.put(Size.LARGE, 36); sizes.put(Size.EXTRALARGE, 40); System.out.println("EnumMap: " + sizes); // Using the remove() Method int value = sizes.remove(Size.MEDIUM); System.out.println("Removed Value: " + value); boolean result = sizes.remove(Size.SMALL, 28); System.out.println("Is the entry (SMALL=28) removed? " + result); System.out.println("Updated EnumMap: " + sizes); ) )
Izhod
EnumMap: (SMALL = 28, MEDIUM = 32, LARGE = 36, EXTRALARGE = 40) Odstranjena vrednost: 32 Ali je vnos (SMALL = 28) odstranjen? Resnično posodobljen EnumMap: (LARGE = 36, EXTRALARGE = 40)
Zamenjajte elemente EnumMap
replace(key, value)
- nadomesti vrednost, povezano z navedenim ključem, z novo vrednostjoreplace(key, old, new)
- staro vrednost nadomesti z novo vrednostjo le, če je stara vrednost že povezana z določenim ključemreplaceAll(function)
- zamenja vsako vrednost zemljevida z rezultatom določene funkcije
import java.util.EnumMap; class Main ( enum Size ( SMALL, MEDIUM, LARGE, EXTRALARGE ) public static void main(String() args) ( // Creating an EnumMap of the Size enum EnumMap sizes = new EnumMap(Size.class); sizes.put(Size.SMALL, 28); sizes.put(Size.MEDIUM, 32); sizes.put(Size.LARGE, 36); sizes.put(Size.EXTRALARGE, 40); System.out.println("EnumMap: " + sizes); // Using the replace() Method sizes.replace(Size.MEDIUM, 30); sizes.replace(Size.LARGE, 36, 34); System.out.println("EnumMap using replace(): " + sizes); // Using the replaceAll() Method sizes.replaceAll((key, oldValue) -> oldValue + 3); System.out.println("EnumMap using replaceAll(): " + sizes); ) )
Izhod
EnumMap: (SMALL=28, MEDIUM=32, LARGE=36, EXTRALARGE=40) EnumMap using replace(): (SMALL=28, MEDIUM=30, LARGE=34, EXTRALARGE=40) EnumMap using replaceAll(): (SMALL=31, MEDIUM=33, LARGE=37, EXTRALARGE=43)
In the above program, notice the statement
sizes.replaceAll((key, oldValue) -> oldValue + 3);
Here, the method accesses all the entries of the map. It then replaces all the values with the new values provided by the lambda expressions.
Other Methods
Method | Description |
---|---|
clone() | Creates a copy of the EnumMap |
containsKey() | Searches the EnumMap for the specified key and returns a boolean result |
containsValue() | Searches the EnumMap for the specified value and returns a boolean result |
size() | Returns the size of the EnumMap |
clear() | Removes all the entries from the EnumMap |
EnumSet Vs. EnumMap
Both the EnumSet and EnumMap
class provides data structures to store enum values. However, there exist some major differences between them.
- Enum set is represented internally as a sequence of bits, whereas the enum map is represented internally as arrays.
- Enum set is created using its predefined methods like
allOf()
,noneOf()
,of()
, etc. However, an enum map is created using its constructor.
Clonable and Serializable Interfaces
The EnumMap
class also implements Cloneable
and Serializable
interfaces.
Cloneable Interface
It allows the EnumMap
class to make a copy of instances of the class.
Serializable Interface
Whenever Java objects need to be transmitted over a network, objects need to be converted into bits or bytes. This is because Java objects cannot be transmitted over the network.
Serializable
Vmesnik omogoča razredi, ki se serialized. To pomeni, da je mogoče predmete razredov, ki se izvajajo, Serializable
pretvoriti v bit ali bajt.