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refactor: apply Factory Enum Pattern for cleaner object instantiation #3523

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refactor: apply Factory Enum Pattern for cleaner object instantiation #3523

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7c3a3a0
refactor: apply Factory Enum Pattern for cleaner object instantiation
prashantpiyush1111 Jun 14, 2026
106b065
style: fix formatting in CoinFactoryTest
prashantpiyush1111 Jun 14, 2026
402abb4
refactor(factory): apply enum-based factory pattern
prashantpiyush1111 Jun 14, 2026
1e2350a
style(factory): fix test indentation
prashantpiyush1111 Jun 14, 2026
569afc8
style(factory): add trailing newline
prashantpiyush1111 Jun 14, 2026
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4 changes: 2 additions & 2 deletions factory/src/main/java/com/iluwatar/factory/App.java
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Original file line number Diff line number Diff line change
Expand Up @@ -40,8 +40,8 @@ public class App {
/** Program main entry point. */
public static void main(String[] args) {
LOGGER.info("The alchemist begins his work.");
var coin1 = CoinFactory.getCoin(CoinType.COPPER);
var coin2 = CoinFactory.getCoin(CoinType.GOLD);
var coin1 = CoinType.COPPER.getInstance();
var coin2 = CoinType.GOLD.getInstance();
LOGGER.info(coin1.getDescription());
LOGGER.info(coin2.getDescription());
}
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12 changes: 12 additions & 0 deletions factory/src/main/java/com/iluwatar/factory/CoinType.java
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Expand Up @@ -25,6 +25,7 @@
package com.iluwatar.factory;

import java.util.function.Supplier;
import lombok.AccessLevel;
import lombok.Getter;
import lombok.RequiredArgsConstructor;

Expand All @@ -36,4 +37,15 @@ public enum CoinType {
GOLD(GoldCoin::new);

private final Supplier<Coin> constructor;

@Getter(AccessLevel.NONE)
private Coin instance;

/** Returns singleton instance of this coin type. */
public Coin getInstance() {
if (instance == null) {
instance = constructor.get();
}
return instance;
}
Comment on lines +45 to +50

@github-actions github-actions Bot Jun 14, 2026

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getInstance() implements lazy initialization without synchronization, which is not thread-safe. In multi-threaded scenarios, two threads could observe instance == null and both create a Coin, potentially leaking one and returning a non-singleton. Consider a thread-safe lazy initialization strategy (e.g., double-checked locking with a volatile field, or initialize at enum construction).

}
14 changes: 13 additions & 1 deletion factory/src/test/java/com/iluwatar/factory/CoinFactoryTest.java
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Expand Up @@ -30,9 +30,21 @@

class CoinFactoryTest {

@Test
void shouldReturnCopperCoinInstance() {
final var copperCoin = CoinType.COPPER.getInstance();
assertTrue(copperCoin instanceof CopperCoin);
}

@Test
void shouldReturnGoldCoinInstance() {
final var goldCoin = CoinFactory.getCoin(CoinType.GOLD);
final var goldCoin = CoinType.GOLD.getInstance();
assertTrue(goldCoin instanceof GoldCoin);
}

@Test
void shouldReturnSameInstanceEachTime() {
assertSame(CoinType.GOLD.getInstance(), CoinType.GOLD.getInstance());
assertSame(CoinType.COPPER.getInstance(), CoinType.COPPER.getInstance());
}
}
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