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docs: update multiton

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Ilkka Seppälä
2024-05-26 15:17:22 +03:00
parent a0f90fa75e
commit 533ca0df6a
1 changed files with 50 additions and 27 deletions
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multiton/README.md
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@@ -20,7 +20,7 @@ The Multiton pattern is a variation of the Singleton design pattern that manages
Real-world example
> The Nazgûl, also called ringwraiths or the Nine Riders, are Sauron's most terrible servants. By definition, there's always nine of them.
> A real-world example of the Multiton pattern is a printer management system in a large office. In this scenario, the office has several printers, each serving a different department. Instead of creating a new printer object every time a printing request is made, the system uses the Multiton pattern to ensure that each department has exactly one printer instance. When a printing request comes from a specific department, the system checks the registry of printer instances and retrieves the existing printer for that department. If no printer exists for that department, it creates one, registers it, and then returns it. This ensures efficient management of printer resources and prevents unnecessary creation of multiple printer instances for the same department.
In plain words
@@ -32,6 +32,8 @@ Wikipedia says
**Programmatic Example**
The Nazgûl, also called ringwraiths or the Nine Riders, are Sauron's most terrible servants. By definition, there's always nine of them.
`Nazgul` is the multiton class.
```java
@@ -73,37 +75,58 @@ public final class Nazgul {
And here's how we access the `Nazgul` instances.
```java
LOGGER.info("Printing out eagerly initialized multiton contents");
LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
LOGGER.info("JI_INDUR={}", Nazgul.getInstance(NazgulName.JI_INDUR));
LOGGER.info("AKHORAHIL={}", Nazgul.getInstance(NazgulName.AKHORAHIL));
LOGGER.info("HOARMURATH={}", Nazgul.getInstance(NazgulName.HOARMURATH));
LOGGER.info("ADUNAPHEL={}", Nazgul.getInstance(NazgulName.ADUNAPHEL));
LOGGER.info("REN={}", Nazgul.getInstance(NazgulName.REN));
LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
public static void main(String[] args) {
// eagerly initialized multiton
LOGGER.info("Printing out eagerly initialized multiton contents");
LOGGER.info("KHAMUL={}", Nazgul.getInstance(NazgulName.KHAMUL));
LOGGER.info("MURAZOR={}", Nazgul.getInstance(NazgulName.MURAZOR));
LOGGER.info("DWAR={}", Nazgul.getInstance(NazgulName.DWAR));
LOGGER.info("JI_INDUR={}", Nazgul.getInstance(NazgulName.JI_INDUR));
LOGGER.info("AKHORAHIL={}", Nazgul.getInstance(NazgulName.AKHORAHIL));
LOGGER.info("HOARMURATH={}", Nazgul.getInstance(NazgulName.HOARMURATH));
LOGGER.info("ADUNAPHEL={}", Nazgul.getInstance(NazgulName.ADUNAPHEL));
LOGGER.info("REN={}", Nazgul.getInstance(NazgulName.REN));
LOGGER.info("UVATHA={}", Nazgul.getInstance(NazgulName.UVATHA));
// enum multiton
LOGGER.info("Printing out enum-based multiton contents");
LOGGER.info("KHAMUL={}", NazgulEnum.KHAMUL);
LOGGER.info("MURAZOR={}", NazgulEnum.MURAZOR);
LOGGER.info("DWAR={}", NazgulEnum.DWAR);
LOGGER.info("JI_INDUR={}", NazgulEnum.JI_INDUR);
LOGGER.info("AKHORAHIL={}", NazgulEnum.AKHORAHIL);
LOGGER.info("HOARMURATH={}", NazgulEnum.HOARMURATH);
LOGGER.info("ADUNAPHEL={}", NazgulEnum.ADUNAPHEL);
LOGGER.info("REN={}", NazgulEnum.REN);
LOGGER.info("UVATHA={}", NazgulEnum.UVATHA);
}
```
Program output:
```
20:35:07.413 [main] INFO com.iluwatar.multiton.App - Printing out eagerly initialized multiton contents
20:35:07.417 [main] INFO com.iluwatar.multiton.App - KHAMUL=com.iluwatar.multiton.Nazgul@48cf768c
20:35:07.419 [main] INFO com.iluwatar.multiton.App - MURAZOR=com.iluwatar.multiton.Nazgul@7960847b
20:35:07.419 [main] INFO com.iluwatar.multiton.App - DWAR=com.iluwatar.multiton.Nazgul@6a6824be
20:35:07.419 [main] INFO com.iluwatar.multiton.App - JI_INDUR=com.iluwatar.multiton.Nazgul@5c8da962
20:35:07.419 [main] INFO com.iluwatar.multiton.App - AKHORAHIL=com.iluwatar.multiton.Nazgul@512ddf17
20:35:07.419 [main] INFO com.iluwatar.multiton.App - HOARMURATH=com.iluwatar.multiton.Nazgul@2c13da15
20:35:07.419 [main] INFO com.iluwatar.multiton.App - ADUNAPHEL=com.iluwatar.multiton.Nazgul@77556fd
20:35:07.419 [main] INFO com.iluwatar.multiton.App - REN=com.iluwatar.multiton.Nazgul@368239c8
20:35:07.420 [main] INFO com.iluwatar.multiton.App - UVATHA=com.iluwatar.multiton.Nazgul@9e89d68
15:16:10.597 [main] INFO com.iluwatar.multiton.App -- Printing out eagerly initialized multiton contents
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- KHAMUL=com.iluwatar.multiton.Nazgul@4141d797
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- MURAZOR=com.iluwatar.multiton.Nazgul@38cccef
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- DWAR=com.iluwatar.multiton.Nazgul@5679c6c6
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- JI_INDUR=com.iluwatar.multiton.Nazgul@27ddd392
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- AKHORAHIL=com.iluwatar.multiton.Nazgul@19e1023e
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- HOARMURATH=com.iluwatar.multiton.Nazgul@7cef4e59
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- ADUNAPHEL=com.iluwatar.multiton.Nazgul@64b8f8f4
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- REN=com.iluwatar.multiton.Nazgul@2db0f6b2
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- UVATHA=com.iluwatar.multiton.Nazgul@3cd1f1c8
15:16:10.600 [main] INFO com.iluwatar.multiton.App -- Printing out enum-based multiton contents
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- KHAMUL=KHAMUL
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- MURAZOR=MURAZOR
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- DWAR=DWAR
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- JI_INDUR=JI_INDUR
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- AKHORAHIL=AKHORAHIL
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- HOARMURATH=HOARMURATH
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- ADUNAPHEL=ADUNAPHEL
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- REN=REN
15:16:10.601 [main] INFO com.iluwatar.multiton.App -- UVATHA=UVATHA
```
## Class diagram
![Multiton](./etc/multiton.png "Multiton")
## Applicability
Use the Multiton pattern when
@@ -131,8 +154,8 @@ Trade-offs:
## Related Patterns
[Singleton](https://java-design-patterns.com/patterns/singleton/): Multiton can be seen as an extension of the Singleton pattern where Singleton allows only one instance of a class, Multiton allows one instance per key.
[Factory Method](https://java-design-patterns.com/patterns/factory-method/): Multiton uses a method to create or retrieve instances, similar to how a Factory Method controls object creation.
* [Singleton](https://java-design-patterns.com/patterns/singleton/): Multiton can be seen as an extension of the Singleton pattern where Singleton allows only one instance of a class, Multiton allows one instance per key.
* [Factory Method](https://java-design-patterns.com/patterns/factory-method/): Multiton uses a method to create or retrieve instances, similar to how a Factory Method controls object creation.
## Credits