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Update flyweight
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‎factory-method/README.md

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@@ -7,7 +7,7 @@ categories: Creational
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language: en
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tags:
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- Extensibility
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- Gang Of Four
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- Gang of Four
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---
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## Also known as

‎flyweight/README.md

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categories: Structural
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language: en
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tags:
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- Gang Of Four
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- Gang of Four
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- Performance
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---
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## Explanation
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Real world example
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Real-world example
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> Alchemist's shop has shelves full of magic potions. Many of the potions are the same so there is
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> no need to create new object for each of them. Instead one object instance can represent multiple
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> shelf items so memory footprint remains small.
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> no need to create a new object for each of them. Instead, one object instance can represent
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> multiple shelf items so the memory footprint remains small.
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In plain words
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**Programmatic example**
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Translating our alchemist shop example from above. First of all we have different potion types:
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Translating our alchemist shop example from above. First of all, we have different potion types:
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```java
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public interface Potion {
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}
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```
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And it can be used as below:
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`AlchemistShop` contains two shelves of magic potions. The potions are created using the
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aforementioned `PotionFactory`.
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```java
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var factory = new PotionFactory();
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factory.createPotion(PotionType.INVISIBILITY).drink(); // You become invisible. (Potion=6566818)
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factory.createPotion(PotionType.HEALING).drink(); // You feel healed. (Potion=648129364)
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factory.createPotion(PotionType.INVISIBILITY).drink(); // You become invisible. (Potion=6566818)
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factory.createPotion(PotionType.HOLY_WATER).drink(); // You feel blessed. (Potion=1104106489)
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factory.createPotion(PotionType.HOLY_WATER).drink(); // You feel blessed. (Potion=1104106489)
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factory.createPotion(PotionType.HEALING).drink(); // You feel healed. (Potion=648129364)
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@Slf4j
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public class AlchemistShop {
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private final List<Potion> topShelf;
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private final List<Potion> bottomShelf;
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public AlchemistShop() {
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var factory = new PotionFactory();
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topShelf = List.of(
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factory.createPotion(PotionType.INVISIBILITY),
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factory.createPotion(PotionType.INVISIBILITY),
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factory.createPotion(PotionType.STRENGTH),
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factory.createPotion(PotionType.HEALING),
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factory.createPotion(PotionType.INVISIBILITY),
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factory.createPotion(PotionType.STRENGTH),
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factory.createPotion(PotionType.HEALING),
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factory.createPotion(PotionType.HEALING)
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);
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bottomShelf = List.of(
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factory.createPotion(PotionType.POISON),
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factory.createPotion(PotionType.POISON),
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factory.createPotion(PotionType.POISON),
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factory.createPotion(PotionType.HOLY_WATER),
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factory.createPotion(PotionType.HOLY_WATER)
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);
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}
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public final List<Potion> getTopShelf() {
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return List.copyOf(this.topShelf);
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}
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public final List<Potion> getBottomShelf() {
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return List.copyOf(this.bottomShelf);
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}
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public void drinkPotions() {
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LOGGER.info("Drinking top shelf potions\n");
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topShelf.forEach(Potion::drink);
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LOGGER.info("Drinking bottom shelf potions\n");
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bottomShelf.forEach(Potion::drink);
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}
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}
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```
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In our scenario, a brave visitor enters the alchemist shop and drinks all the potions.
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```java
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// create the alchemist shop with the potions
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var alchemistShop = new AlchemistShop();
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// a brave visitor enters the alchemist shop and drinks all the potions
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alchemistShop.drinkPotions();
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```
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Program output:
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```java
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You become invisible. (Potion=6566818)
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You feel healed. (Potion=648129364)
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You become invisible. (Potion=6566818)
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You feel blessed. (Potion=1104106489)
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You feel blessed. (Potion=1104106489)
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You feel healed. (Potion=648129364)
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Drinking top shelf potions
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You become invisible. (Potion=1509514333)
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You become invisible. (Potion=1509514333)
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You feel strong. (Potion=739498517)
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You feel healed. (Potion=125130493)
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You become invisible. (Potion=1509514333)
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You feel strong. (Potion=739498517)
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You feel healed. (Potion=125130493)
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You feel healed. (Potion=125130493)
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Drinking bottom shelf potions
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Urgh! This is poisonous. (Potion=166239592)
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Urgh! This is poisonous. (Potion=166239592)
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Urgh! This is poisonous. (Potion=166239592)
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You feel blessed. (Potion=991505714)
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You feel blessed. (Potion=991505714)
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```
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## Class diagram
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* An application uses a large number of objects.
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* Storage costs are high because of the sheer quantity of objects.
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* Most object state can be made extrinsic.
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* Many groups of objects may be replaced by relatively few shared objects once extrinsic state is
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removed.
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* Most of the object state can be made extrinsic.
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* Many groups of objects may be replaced by relatively few shared objects once the extrinsic state
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is removed.
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* The application doesn't depend on object identity. Since flyweight objects may be shared, identity
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tests will return true for conceptually distinct objects.
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## Real world examples
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## Known uses
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* [java.lang.Integer#valueOf(int)](http://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#valueOf%28int%29) and similarly for Byte, Character and other wrapped types.
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‎flyweight/src/main/java/com/iluwatar/flyweight/AlchemistShop.java

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@@ -78,12 +78,12 @@ public final List<Potion> getBottomShelf() {
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}
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/**
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* Enumerate potions.
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* Drink all the potions.
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*/
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public void enumerate() {
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LOGGER.info("Enumerating top shelf potions\n");
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public void drinkPotions() {
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LOGGER.info("Drinking top shelf potions");
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topShelf.forEach(Potion::drink);
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LOGGER.info("Enumerating bottom shelf potions\n");
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LOGGER.info("Drinking bottom shelf potions");
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bottomShelf.forEach(Potion::drink);
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}
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}

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

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* @param args command line args
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*/
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public static void main(String[] args) {
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// create the alchemist shop with the potions
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var alchemistShop = new AlchemistShop();
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alchemistShop.enumerate();
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// a brave visitor enters the alchemist shop and drinks all the potions
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alchemistShop.drinkPotions();
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}
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}

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