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task: Update Multiton example (iluwatar#1950)
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Co-authored-by: Subhrodip Mohanta <[email protected]>
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iluwatar and ohbus authored Jan 24, 2022
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71 changes: 48 additions & 23 deletions multiton/README.md
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Expand Up @@ -15,18 +15,18 @@ Registry

## Intent

Ensure a class only has limited number of instances and provide a global point of access to them.
Ensure a class only has a limited number of instances and provide a global point of access to them.

## Explanation

Real world example
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.
> definition, there's always nine of them.
In plain words

> Multiton pattern ensures there's predefined amount of instances available globally.
> Multiton pattern ensures there are a predefined amount of instances available globally.
Wikipedia says

Expand Down Expand Up @@ -81,29 +81,54 @@ public final class Nazgul {
And here's how we access the `Nazgul` instances.

```java
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));
// 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:

```
KHAMUL=com.iluwatar.multiton.Nazgul@2b214b94
MURAZOR=com.iluwatar.multiton.Nazgul@17814b1c
DWAR=com.iluwatar.multiton.Nazgul@7ac9af2a
JI_INDUR=com.iluwatar.multiton.Nazgul@7bb004b8
AKHORAHIL=com.iluwatar.multiton.Nazgul@78e89bfe
HOARMURATH=com.iluwatar.multiton.Nazgul@652ce654
ADUNAPHEL=com.iluwatar.multiton.Nazgul@522ba524
REN=com.iluwatar.multiton.Nazgul@29c5ee1d
UVATHA=com.iluwatar.multiton.Nazgul@15cea7b0
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
20:35:07.420 [main] INFO com.iluwatar.multiton.App - Printing out enum-based multiton contents
20:35:07.420 [main] INFO com.iluwatar.multiton.App - KHAMUL=KHAMUL
20:35:07.420 [main] INFO com.iluwatar.multiton.App - MURAZOR=MURAZOR
20:35:07.420 [main] INFO com.iluwatar.multiton.App - DWAR=DWAR
20:35:07.420 [main] INFO com.iluwatar.multiton.App - JI_INDUR=JI_INDUR
20:35:07.421 [main] INFO com.iluwatar.multiton.App - AKHORAHIL=AKHORAHIL
20:35:07.421 [main] INFO com.iluwatar.multiton.App - HOARMURATH=HOARMURATH
20:35:07.421 [main] INFO com.iluwatar.multiton.App - ADUNAPHEL=ADUNAPHEL
20:35:07.421 [main] INFO com.iluwatar.multiton.App - REN=REN
20:35:07.421 [main] INFO com.iluwatar.multiton.App - UVATHA=UVATHA
```

## Class diagram
Expand All @@ -114,5 +139,5 @@ UVATHA=com.iluwatar.multiton.Nazgul@15cea7b0

Use the Multiton pattern when

* There must be specific number of instances of a class, and they must be accessible to clients from
* There must be a specific number of instances of a class, and they must be accessible to clients from
a well-known access point.
8 changes: 5 additions & 3 deletions multiton/src/main/java/com/iluwatar/multiton/App.java
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Expand Up @@ -26,13 +26,13 @@
import lombok.extern.slf4j.Slf4j;

/**
* Whereas Singleton design pattern introduces single globally accessible object the Multiton
* Whereas Singleton design pattern introduces single globally accessible object, the Multiton
* pattern defines many globally accessible objects. The client asks for the correct instance from
* the Multiton by passing an enumeration as parameter.
* the Multiton by passing an enumeration as a parameter.
*
* <p>There is more than one way to implement the multiton design pattern. In the first example
* {@link Nazgul} is the Multiton and we can ask single {@link Nazgul} from it using {@link
* NazgulName}. The {@link Nazgul}s are statically initialized and stored in concurrent hash map.
* NazgulName}. The {@link Nazgul}s are statically initialized and stored in a concurrent hash map.
*
* <p>In the enum implementation {@link NazgulEnum} is the multiton. It is static and mutable
* because of the way java supports enums.
Expand All @@ -47,6 +47,7 @@ public class App {
*/
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));
Expand All @@ -58,6 +59,7 @@ public static void main(String[] args) {
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);
Expand Down
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Expand Up @@ -48,5 +48,4 @@ void testGetInstance() {
assertEquals(name, nazgul.getName());
}
}

}

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