Differences

Kinds of item
- all items
   - max quality is 50, other than legendary

1. Legendary
   - before expiry -> doesn't change quality
   - after expiry -> doesn't change quality

2 conjured
   - before expiry -> quality decreases x2
   - after expiry -> quality decrease x4
3 normal
   - before expiry -> quality decreases x1
   - after expiry -> quality decrease x2
4 agedBrie
   - before expiry -> quality increase x1
   - after expiry -> quality increase x2
5 backstagePass
   - before expiry ->
       - sellIn > 10 -> quality increase x1
       - sellIn <= 10 -> quality increase x2
   - after expiry -> quality = 0

gilded_rose_refactored_v1

class GildedRose {
    Item[] items;

    public GildedRose(Item[] items) {
        this.items = items;
    }

    public boolean isAgedBrie(Item item){
        return item.name.equals("Aged Brie");
    }

    public boolean isBackstagePass(Item item){
        return item.name.equals("Backstage passes to a TAFKAL80ETC concert");
    }

    public boolean isSulfuras(Item item){
        return item.name.equals("Sulfuras, Hand of Ragnaros");
    }

    public boolean isConjured(Item item){
        return item.name.startsWith("Conjured");
    }

    public void incrementQuality(Item item){
        if (item.quality < 50) {
            item.quality += 1;
        }
    }

    public void decrementQuality(Item item){
        if (item.quality > 0) {
            item.quality -= 1;
        }
    }

    public void updateQuality() {
        for (int i = 0; i < items.length; i++) {
            Item item = items[i];
            if (!isAgedBrie(item) && !isBackstagePass(item)) {
                if (!isSulfuras(item)) {
                    decrementQuality(item);
                    if(isConjured(item)){
                        decrementQuality(item);
                    }
                }
            } else {
                incrementQuality(item);
                if (isBackstagePass(item)) {
                    if (items[i].sellIn < 11) {
                        incrementQuality(item);
                    }
                    if (items[i].sellIn < 6) {
                        incrementQuality(item);
                    }
                }
            }

            if (!isSulfuras(item)) {
                items[i].sellIn = items[i].sellIn - 1;
            }

            if (items[i].sellIn < 0) {
                if(isAgedBrie(item)){
                    incrementQuality(item);
                } else if (isBackstagePass(item)){
                    item.quality = 0;
                } else if(isSulfuras(item)){

                } else {
                    decrementQuality(item);
                    if(isConjured(item)){
                        decrementQuality(item);
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        Item[] items = {
            new Item("Aged Brie", 3, 35),
            new Item("Sulfuras, Hand of Ragnaros", 0, 80),
            new Item("Backstage passes to a TAFKAL80ETC concert", 12, 30),
            new Item("Backstage passes to a TAFKAL80ETC concert", 7, 30),
            new Item("Backstage passes to a TAFKAL80ETC concert", 2, 30),
            new Item("Cake", 3, 10),
            new Item("Conjured Cake", 3, 10)
        };

        GildedRose inn = new GildedRose(items);

        for(int day = 0; day < 8; day++){
            System.out.println("Day " + day);
            Item[] listOfItems = inn.items;

            System.out.println("Name , SellIn , Quality");
            for(Item item: listOfItems){
                System.out.println(item.name + " , " + item.sellIn + " , " + item.quality);
            }
            System.out.println("-----------------------------");
            inn.updateQuality();
        }
    }
}