Add AbstractItemUpdateStrategy and refactor ItemUpdateStrategy subclasses

Java/src/main/java/com/gildedrose/strategy/AbstractItemUpdateStrategy.java

@@ -0,0 +1,18 @@
+package com.gildedrose.strategy;
+
+import com.gildedrose.Item;
+
+public abstract class AbstractItemUpdateStrategy implements ItemUpdateStrategy {
+    protected static final int MAX_QUALITY = 50;
+    protected static final int MIN_QUALITY = 0;
+
+    protected void incrementQualityIfLessThanMax(Item item) {
+        if (item.quality < MAX_QUALITY) {
+            item.quality += 1;
+        }
+    }
+
+    protected void decrementSellIn(Item item) {
+        item.sellIn -= 1;
+    }
+}

Java/src/main/java/com/gildedrose/strategy/AgedBrieUpdateStrategy.java

@@ -2,19 +2,14 @@ package com.gildedrose.strategy;
 
 import com.gildedrose.Item;
 
-public class AgedBrieUpdateStrategy implements ItemUpdateStrategy {
+public class AgedBrieUpdateStrategy extends AbstractItemUpdateStrategy {
     @Override
     public void update(Item item) {
-        if (item.quality < 50) {
+        incrementQualityIfLessThanMax(item);
-            item.quality += 1;
+        decrementSellIn(item);
-        }
-
-        item.sellIn -= 1;
 
         if (item.sellIn < 0) {
-            if (item.quality < 50) {
+            incrementQualityIfLessThanMax(item);
-                item.quality += 1;
-            }
         }
     }
 }

Java/src/main/java/com/gildedrose/strategy/BackstagePassesUpdateStrategy.java

@@ -2,29 +2,23 @@ package com.gildedrose.strategy;
 
 import com.gildedrose.Item;
 
-public class BackstagePassesUpdateStrategy implements ItemUpdateStrategy {
+public class BackstagePassesUpdateStrategy extends AbstractItemUpdateStrategy {
     @Override
     public void update(Item item) {
-        if (item.quality < 50) {
+        incrementQualityIfLessThanMax(item);
-            item.quality += 1;
 
-            if (item.sellIn < 11) {
+        if (item.sellIn < 11) {
-                if (item.quality < 50) {
+            incrementQualityIfLessThanMax(item);
-                    item.quality += 1;
-                }
-            }
-
-            if (item.sellIn < 6) {
-                if (item.quality < 50) {
-                    item.quality += 1;
-                }
-            }
         }
 
-        item.sellIn -= 1;
+        if (item.sellIn < 6) {
+            incrementQualityIfLessThanMax(item);
+        }
+
+        decrementSellIn(item);
 
         if (item.sellIn < 0) {
-            item.quality = 0;
+            item.quality = MIN_QUALITY;
         }
     }
 }

Java/src/main/java/com/gildedrose/strategy/StandardItemUpdateStrategy.java

@@ -2,14 +2,14 @@ package com.gildedrose.strategy;
 
 import com.gildedrose.Item;
 
-public class StandardItemUpdateStrategy implements ItemUpdateStrategy {
+public class StandardItemUpdateStrategy extends AbstractItemUpdateStrategy {
     @Override
     public void update(Item item) {
-        item.sellIn -= 1;
+        decrementSellIn(item);
-        if (item.quality > 0) {
+        if (item.quality > MIN_QUALITY) {
             item.quality -= 1;
         }
-        if (item.sellIn < 0 && item.quality > 0) {
+        if (item.sellIn < 0 && item.quality > MIN_QUALITY) {
             item.quality -= 1;
         }
     }

Java/src/main/java/com/gildedrose/strategy/SulfurasUpdateStrategy.java

@@ -2,7 +2,7 @@ package com.gildedrose.strategy;
 
 import com.gildedrose.Item;
 
-public class SulfurasUpdateStrategy implements ItemUpdateStrategy {
+public class SulfurasUpdateStrategy extends AbstractItemUpdateStrategy {
     @Override
     public void update(Item item) {
         // "Sulfuras, Hand of Ragnaros"는 판매일과 품질이 변하지 않음