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task: Update Multiton example (iluwatar#1950)
Co-authored-by: Subhrodip Mohanta <[email protected]>
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‎multiton/README.md‎

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@@ -15,18 +15,18 @@ Registry
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## Intent
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Ensure a class only has limited number of instances and provide a global point of access to them.
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Ensure a class only has a limited number of instances and provide a global point of access to them.
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## Explanation
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Real world example
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Real-world example
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> The Nazgûl, also called ringwraiths or the Nine Riders, are Sauron's most terrible servants. By
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> definition there's always nine of them.
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> definition, there's always nine of them.
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In plain words
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> Multiton pattern ensures there's predefined amount of instances available globally.
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> Multiton pattern ensures there are a predefined amount of instances available globally.
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Wikipedia says
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@@ -81,29 +81,54 @@ public final class Nazgul {
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And here's how we access the `Nazgul` instances.
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```java
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LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
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LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
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LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
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LOGGER.info("JI_INDUR={}", Nazgul.getInstance(NazgulName.JI_INDUR));
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LOGGER.info("AKHORAHIL={}", Nazgul.getInstance(NazgulName.AKHORAHIL));
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LOGGER.info("HOARMURATH={}", Nazgul.getInstance(NazgulName.HOARMURATH));
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LOGGER.info("ADUNAPHEL={}", Nazgul.getInstance(NazgulName.ADUNAPHEL));
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LOGGER.info("REN={}", Nazgul.getInstance(NazgulName.REN));
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LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
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// eagerly initialized multiton
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LOGGER.info("Printing out eagerly initialized multiton contents");
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LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
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LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
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LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
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LOGGER.info("JI_INDUR={}", Nazgul.getInstance(NazgulName.JI_INDUR));
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LOGGER.info("AKHORAHIL={}", Nazgul.getInstance(NazgulName.AKHORAHIL));
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LOGGER.info("HOARMURATH={}", Nazgul.getInstance(NazgulName.HOARMURATH));
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LOGGER.info("ADUNAPHEL={}", Nazgul.getInstance(NazgulName.ADUNAPHEL));
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LOGGER.info("REN={}", Nazgul.getInstance(NazgulName.REN));
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LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
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// enum multiton
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LOGGER.info("Printing out enum-based multiton contents");
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LOGGER.info("KHAMUL={}", NazgulEnum.KHAMUL);
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LOGGER.info("MURAZOR={}", NazgulEnum.MURAZOR);
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LOGGER.info("DWAR={}", NazgulEnum.DWAR);
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LOGGER.info("JI_INDUR={}", NazgulEnum.JI_INDUR);
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LOGGER.info("AKHORAHIL={}", NazgulEnum.AKHORAHIL);
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LOGGER.info("HOARMURATH={}", NazgulEnum.HOARMURATH);
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LOGGER.info("ADUNAPHEL={}", NazgulEnum.ADUNAPHEL);
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LOGGER.info("REN={}", NazgulEnum.REN);
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LOGGER.info("UVATHA={}", NazgulEnum.UVATHA);
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```
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Program output:
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```
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KHAMUL=com.iluwatar.multiton.Nazgul@2b214b94
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MURAZOR=com.iluwatar.multiton.Nazgul@17814b1c
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DWAR=com.iluwatar.multiton.Nazgul@7ac9af2a
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JI_INDUR=com.iluwatar.multiton.Nazgul@7bb004b8
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AKHORAHIL=com.iluwatar.multiton.Nazgul@78e89bfe
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HOARMURATH=com.iluwatar.multiton.Nazgul@652ce654
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ADUNAPHEL=com.iluwatar.multiton.Nazgul@522ba524
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REN=com.iluwatar.multiton.Nazgul@29c5ee1d
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UVATHA=com.iluwatar.multiton.Nazgul@15cea7b0
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20:35:07.413 [main] INFO com.iluwatar.multiton.App - Printing out eagerly initialized multiton contents
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20:35:07.417 [main] INFO com.iluwatar.multiton.App - KHAMUL=com.iluwatar.multiton.Nazgul@48cf768c
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - MURAZOR=com.iluwatar.multiton.Nazgul@7960847b
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - DWAR=com.iluwatar.multiton.Nazgul@6a6824be
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - JI_INDUR=com.iluwatar.multiton.Nazgul@5c8da962
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - AKHORAHIL=com.iluwatar.multiton.Nazgul@512ddf17
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - HOARMURATH=com.iluwatar.multiton.Nazgul@2c13da15
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - ADUNAPHEL=com.iluwatar.multiton.Nazgul@77556fd
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20:35:07.419 [main] INFO com.iluwatar.multiton.App - REN=com.iluwatar.multiton.Nazgul@368239c8
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - UVATHA=com.iluwatar.multiton.Nazgul@9e89d68
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - Printing out enum-based multiton contents
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - KHAMUL=KHAMUL
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - MURAZOR=MURAZOR
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - DWAR=DWAR
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20:35:07.420 [main] INFO com.iluwatar.multiton.App - JI_INDUR=JI_INDUR
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20:35:07.421 [main] INFO com.iluwatar.multiton.App - AKHORAHIL=AKHORAHIL
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20:35:07.421 [main] INFO com.iluwatar.multiton.App - HOARMURATH=HOARMURATH
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20:35:07.421 [main] INFO com.iluwatar.multiton.App - ADUNAPHEL=ADUNAPHEL
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20:35:07.421 [main] INFO com.iluwatar.multiton.App - REN=REN
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20:35:07.421 [main] INFO com.iluwatar.multiton.App - UVATHA=UVATHA
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```
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## Class diagram
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Use the Multiton pattern when
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* There must be specific number of instances of a class, and they must be accessible to clients from
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* There must be a specific number of instances of a class, and they must be accessible to clients from
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a well-known access point.

‎multiton/src/main/java/com/iluwatar/multiton/App.java‎

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import lombok.extern.slf4j.Slf4j;
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/**
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* Whereas Singleton design pattern introduces single globally accessible object the Multiton
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* Whereas Singleton design pattern introduces single globally accessible object, the Multiton
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* pattern defines many globally accessible objects. The client asks for the correct instance from
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* the Multiton by passing an enumeration as parameter.
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* the Multiton by passing an enumeration as a parameter.
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*
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* <p>There is more than one way to implement the multiton design pattern. In the first example
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* {@link Nazgul} is the Multiton and we can ask single {@link Nazgul} from it using {@link
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* NazgulName}. The {@link Nazgul}s are statically initialized and stored in concurrent hash map.
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* NazgulName}. The {@link Nazgul}s are statically initialized and stored in a concurrent hash map.
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*
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* <p>In the enum implementation {@link NazgulEnum} is the multiton. It is static and mutable
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* because of the way java supports enums.
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*/
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public static void main(String[] args) {
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// eagerly initialized multiton
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LOGGER.info("Printing out eagerly initialized multiton contents");
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LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
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LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
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LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
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LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
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// enum multiton
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LOGGER.info("Printing out enum-based multiton contents");
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LOGGER.info("KHAMUL={}", NazgulEnum.KHAMUL);
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LOGGER.info("MURAZOR={}", NazgulEnum.MURAZOR);
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LOGGER.info("DWAR={}", NazgulEnum.DWAR);

‎multiton/src/test/java/com/iluwatar/multiton/NazgulTest.java‎

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assertEquals(name, nazgul.getName());
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}
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}
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}

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