Implement the Creational Design Patterns (#3)

* Implement the Factory Method Design Pattern

* Implement the Abstract Factory Design Pattern

* Implement the Builder Design Pattern

* Implement the Object Pool Design Pattern

* Implement the Prototype Design Pattern

* Implement the Singleton Design Pattern

Author: subhatav

src/practice/creational/builder/BuilderDemo.java

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+package practice.creational.builder;
+
+import practice.creational.builder.CustomPizza.PizzaChef;
+import practice.creational.builder.PizzaElement.DoughType;
+import practice.creational.builder.PizzaElement.SauceType;
+import practice.creational.builder.PizzaElement.ToppingType;
+
+/**
+ * Example of Builder Design Pattern
+ */
+public final class BuilderDemo {
+
+  public static void main(final String... arguments) {
+
+    new PizzaChef(DoughType.BAKED).setSauceType(SauceType.HOT)
+        .setTopping(ToppingType.CAPSICUM_MUSHROOM).cookPizza().eatPizza();
+
+    new PizzaChef(DoughType.CROSS).setSauceType(SauceType.MILD)
+        .setTopping(ToppingType.CHEESE_CORN_TOMATO).cookPizza().eatPizza();
+  }
+}

src/practice/creational/builder/CustomPizza.java

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+package practice.creational.builder;
+
+import lombok.AccessLevel;
+import lombok.EqualsAndHashCode;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+import lombok.Setter;
+import lombok.ToString;
+import lombok.experimental.Accessors;
+import lombok.extern.java.Log;
+
+@Log
+@ToString
+@EqualsAndHashCode
+@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+public final class CustomPizza {
+
+  @NonNull
+  private final PizzaElement.DoughType doughType;
+  @NonNull
+  private final PizzaElement.SauceType sauceType;
+  @NonNull
+  private final PizzaElement.ToppingType topping;
+
+  public void eatPizza() {
+    log.info("EATING Pizza => " + this);
+  }
+
+  @Setter
+  @ToString
+  @EqualsAndHashCode
+  @RequiredArgsConstructor
+  @Accessors(chain = true)
+  protected static final class PizzaChef {
+
+    @NonNull
+    private final PizzaElement.DoughType doughType;
+
+    private PizzaElement.SauceType sauceType;
+    private PizzaElement.ToppingType topping;
+
+    public CustomPizza cookPizza() {
+      log.info("COOKING Pizza => " + this); // In OVEN
+      return new CustomPizza(doughType, sauceType, topping);
+    }
+  }
+}

src/practice/creational/builder/PizzaElement.java

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+package practice.creational.builder;
+
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
+
+@ToString
+@EqualsAndHashCode
+public final class PizzaElement {
+
+  protected enum DoughType {
+
+    BAKED, CROSS
+  }
+
+  protected enum SauceType {
+
+    HOT, MILD
+  }
+
+  protected enum ToppingType {
+
+    CAPSICUM_MUSHROOM, CHEESE_CORN_TOMATO
+  }
+}

src/practice/creational/factory/BronzeCoin.java

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+package practice.creational.factory;
+
+import lombok.EqualsAndHashCode;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+import lombok.ToString;
+import lombok.extern.java.Log;
+
+@Log
+@ToString
+@EqualsAndHashCode
+@RequiredArgsConstructor
+public final class BronzeCoin implements MetalCoin {
+
+  private static final Integer PRINCIPAL_COST = 2_500;
+
+  @NonNull
+  private final Float demandFactor; // Price MULTIPLIER
+
+  @Override
+  public void printWorth() {
+    final var value = (PRINCIPAL_COST * demandFactor) + " INR";
+    log.info("Monetary WORTH of BRONZE Coin => " + value);
+  }
+}

src/practice/creational/factory/CoinFactory.java

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+package practice.creational.factory;
+
+import lombok.EqualsAndHashCode;
+import lombok.NonNull;
+import lombok.extern.java.Log;
+
+@Log
+@EqualsAndHashCode
+public abstract sealed class CoinFactory permits MassFactory, RareFactory {
+
+  protected abstract Float getDemandFactor(); // Get SPECIFIC multiplier
+
+  public MetalCoin mintCoin(@NonNull final CoinType coinType) {
+    var mintedCoin = coinType.getCreator().apply(getDemandFactor());
+    log.info("CATEGORY of Minted COIN => [" + mintedCoin + "]");
+    return mintedCoin; // Return the SPECIFIC category of minted COIN
+  }
+}

src/practice/creational/factory/CoinType.java

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+package practice.creational.factory;
+
+import java.util.function.Function;
+import lombok.Getter;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+
+@Getter
+@RequiredArgsConstructor
+public enum CoinType {
+
+  BRONZE(BronzeCoin::new), // Holds CONSTRUCTOR
+  SILVER(SilverCoin::new); // Holds CONSTRUCTOR
+
+  @NonNull
+  private final Function<Float, MetalCoin> creator;
+}

src/practice/creational/factory/FactoryDemo.java

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+package practice.creational.factory;
+
+import java.util.List;
+
+/**
+ * Example of Factory Method Design Pattern
+ */
+public final class FactoryDemo {
+
+  public static void main(final String... arguments) {
+
+    createCoinMints().forEach(coinFactory -> {
+      coinFactory.mintCoin(CoinType.BRONZE).printWorth();
+      coinFactory.mintCoin(CoinType.SILVER).printWorth();
+    });
+  }
+
+  private static List<CoinFactory> createCoinMints() {
+    return List.of(new MassFactory(), new RareFactory());
+  }
+}

src/practice/creational/factory/MassFactory.java

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+package practice.creational.factory;
+
+import lombok.NoArgsConstructor;
+import lombok.NonNull;
+import lombok.ToString;
+import lombok.extern.java.Log;
+
+@Log
+@ToString
+@NoArgsConstructor
+public final class MassFactory extends CoinFactory {
+
+  private static final Float DEMAND_FACTOR = 1.2F;
+
+  @Override
+  protected Float getDemandFactor() {
+    return DEMAND_FACTOR;
+  }
+
+  @Override
+  public MetalCoin mintCoin(@NonNull final CoinType coinType) {
+    log.info("Current FACTORY for MINT => [" + this + "]");
+    return super.mintCoin(coinType); // Get CURRENT minted COIN
+  }
+}

src/practice/creational/factory/MetalCoin.java

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+package practice.creational.factory;
+
+public sealed interface MetalCoin permits BronzeCoin, SilverCoin {
+
+  void printWorth(); // Prints monetary WORTH of minted Metal COIN
+}

src/practice/creational/factory/RareFactory.java

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+package practice.creational.factory;
+
+import lombok.NoArgsConstructor;
+import lombok.NonNull;
+import lombok.ToString;
+import lombok.extern.java.Log;
+
+@Log
+@ToString
+@NoArgsConstructor
+public final class RareFactory extends CoinFactory {
+
+  private static final Float DEMAND_FACTOR = 4.8F;
+
+  @Override
+  protected Float getDemandFactor() {
+    return DEMAND_FACTOR;
+  }
+
+  @Override
+  public MetalCoin mintCoin(@NonNull final CoinType coinType) {
+    log.info("Current FACTORY for MINT => [" + this + "]");
+    return super.mintCoin(coinType); // Get CURRENT minted COIN
+  }
+}