修改Item且增加4支subclass

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

@@ -0,0 +1,20 @@
+package com.gildedrose;
+
+public class AgedBrieItem extends Item {
+
+	public AgedBrieItem(String name, int sellIn, int quality) {
+		super(name, sellIn, quality);
+	}
+
+	@Override
+	public void update() {
+		this.sellIn = this.sellIn - 1;
+
+		this.increaseQuality();
+
+		if (this.sellIn < 0) {
+			this.increaseQuality();
+		}
+	}
+
+}

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

@@ -0,0 +1,28 @@
+package com.gildedrose;
+
+public class BackstagePassesItem extends Item {
+
+	public BackstagePassesItem(String name, int sellIn, int quality) {
+		super(name, sellIn, quality);
+	}
+
+	@Override
+	public void update() {
+		this.sellIn = this.sellIn - 1;
+
+		this.increaseQuality();
+
+		if (this.sellIn < 10) {
+			this.increaseQuality();
+		}
+
+		if (this.sellIn < 5) {
+			this.increaseQuality();
+		}
+
+		if (this.sellIn < 0) {
+			this.quality = this.quality - this.quality;
+		}
+	}
+
+}

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

@@ -14,6 +14,22 @@ public class Item {
 		this.quality = quality;
 	}
 
+	public void update() {
+
+	}
+
+	public void decreaseQuality() {
+		if (this.quality > 0) {
+			this.quality = this.quality - 1;
+		}
+	}
+
+	public void increaseQuality() {
+		if (this.quality < 50) {
+			this.quality = this.quality + 1;
+		}
+	}
+
 	@Override
 	public String toString() {
 		return this.name + ", " + this.sellIn + ", " + this.quality;

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

@@ -0,0 +1,19 @@
+package com.gildedrose;
+
+public class NormalItem extends Item {
+
+	public NormalItem(String name, int sellIn, int quality) {
+		super(name, sellIn, quality);
+	}
+
+	@Override
+	public void update() {
+		this.sellIn = this.sellIn - 1;
+
+		this.decreaseQuality();
+		if (this.sellIn < 0) {
+			this.decreaseQuality();
+		}
+	}
+
+}

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

@@ -0,0 +1,13 @@
+package com.gildedrose;
+
+public class SulfurasItem extends Item {
+
+	public SulfurasItem(String name, int sellIn, int quality) {
+		super(name, sellIn, quality);
+	}
+
+	@Override
+	public void update() {
+	}
+
+}