Use interface over abstract class

Java/src/main/java/com/gildedrose/AgedBrieItemHandler.java

@@ -1,6 +1,6 @@
 package com.gildedrose;
 
-public class AgedBrieItemHandler extends ItemHandler {
+public class AgedBrieItemHandler implements ItemHandler {
 
   public AgedBrieItemHandler() {}
 

Java/src/main/java/com/gildedrose/BackstagePassesItemHandler.java

@@ -1,6 +1,6 @@
 package com.gildedrose;
 
-public class BackstagePassesItemHandler extends ItemHandler {
+public class BackstagePassesItemHandler implements ItemHandler {
 
   @Override
   public void handleDay(Item item) {

Java/src/main/java/com/gildedrose/ConjuredItemHandler.java

@@ -1,6 +1,7 @@
 package com.gildedrose;
 
-public class ConjuredItemHandler extends ItemHandler {
+public class ConjuredItemHandler implements ItemHandler {
+
   @Override
   public void handleDay(Item item) {
     item.quality -= 2;

Java/src/main/java/com/gildedrose/GenericItemHandler.java

@@ -1,6 +1,6 @@
 package com.gildedrose;
 
-public class GenericItemHandler extends ItemHandler {
+public class GenericItemHandler implements ItemHandler {
 
   @Override
   public void handleDay(Item item) {

Java/src/main/java/com/gildedrose/ItemHandler.java

@@ -1,7 +1,5 @@
 package com.gildedrose;
 
-public abstract class ItemHandler {
+public interface ItemHandler {
-
+  void handleDay(Item item);
-  public void handleDay(Item item) {
-  }
 }

Java/src/main/java/com/gildedrose/ItemHandlerFactory.java

@@ -4,7 +4,6 @@ import java.lang.reflect.InvocationTargetException;
 import java.util.Map;
 
 public class ItemHandlerFactory {
-
   private static final Map<ItemType, Class<? extends ItemHandler>> ITEM_HANDLER_MAP = Map.of(
     ItemType.AGED_BRIE,
     AgedBrieItemHandler.class,

Java/src/main/java/com/gildedrose/ItemType.java

@@ -18,7 +18,9 @@ public enum ItemType {
   public static ItemType forDisplayName(String displayName) {
     return Arrays
       .stream(ItemType.values())
-      .filter(itemType -> itemType.getDisplayName().equals(displayName)).findFirst().orElse(GENERIC);
+      .filter(itemType -> itemType.getDisplayName().equals(displayName))
+      .findFirst()
+      .orElse(GENERIC);
   }
 
   public String getDisplayName() {

Java/src/main/java/com/gildedrose/SulfurasItemHandler.java

@@ -1,3 +1,7 @@
 package com.gildedrose;
 
-public class SulfurasItemHandler extends ItemHandler {}
+public class SulfurasItemHandler implements ItemHandler {
+
+  @Override
+  public void handleDay(Item item) {}
+}

Java/src/test/java/com/gildedrose/GildedRoseTest.java

@@ -1,15 +1,17 @@
 package com.gildedrose;
 
-import org.junit.jupiter.api.Test;
-
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import org.junit.jupiter.api.Test;
+
 class GildedRoseTest {
   private static final int SULFURAS_QUALITY = 80;
 
   @Test
   public void agedBrieIncreasesInQualityByOneEachDay() {
-    Item[] items = new Item[]{new Item(ItemType.AGED_BRIE.getDisplayName(), 2, 0)};
+    Item[] items = new Item[] {
+      new Item(ItemType.AGED_BRIE.getDisplayName(), 2, 0)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(1, app.items.get(0).quality);
@@ -109,7 +111,9 @@ class GildedRoseTest {
 
   @Test
   public void qualityIsNeverOverFiftyForAgedBrie() {
-    Item[] items = new Item[]{new Item(ItemType.AGED_BRIE.getDisplayName(), 5, 50)};
+    Item[] items = new Item[] {
+      new Item(ItemType.AGED_BRIE.getDisplayName(), 5, 50)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(50, app.items.get(0).quality);
@@ -121,7 +125,9 @@ class GildedRoseTest {
 
   @Test
   public void qualityIsNeverOverFiftyForBackstagePasses() {
-    Item[] items = new Item[]{new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 5, 50)};
+    Item[] items = new Item[] {
+      new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 5, 50)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(50, app.items.get(0).quality);
@@ -157,7 +163,9 @@ class GildedRoseTest {
 
   @Test
   public void sellInDateDecreasesByOneEachDayForAgedBrie() {
-    Item[] items = new Item[]{new Item(ItemType.AGED_BRIE.getDisplayName(), 5, 1)};
+    Item[] items = new Item[] {
+      new Item(ItemType.AGED_BRIE.getDisplayName(), 5, 1)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(4, app.items.get(0).sellIn);
@@ -169,7 +177,9 @@ class GildedRoseTest {
 
   @Test
   public void sellInDateDecreasesByOneEachDayForBackstagePasses() {
-    Item[] items = new Item[]{new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 5, 1)};
+    Item[] items = new Item[] {
+      new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 5, 1)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(4, app.items.get(0).sellIn);
@@ -205,7 +215,9 @@ class GildedRoseTest {
 
   @Test
   public void sellInDateCanBeNegativeForAgedBrie() {
-    Item[] items = new Item[]{new Item(ItemType.AGED_BRIE.getDisplayName(), 1, 1)};
+    Item[] items = new Item[] {
+      new Item(ItemType.AGED_BRIE.getDisplayName(), 1, 1)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(0, app.items.get(0).sellIn);
@@ -217,7 +229,9 @@ class GildedRoseTest {
 
   @Test
   public void sellInDateCanBeNegativeForBackStagePasses() {
-    Item[] items = new Item[]{new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 1, 1)};
+    Item[] items = new Item[] {
+      new Item(ItemType.BACKSTAGE_PASSES.getDisplayName(), 1, 1)
+    };
     GildedRose app = new GildedRose(items);
     app.updateQuality();
     assertEquals(0, app.items.get(0).sellIn);