javaで戻り値に配列を設定したい

class TextQuestCard{
	
	String name;
	int level;
	int conditionsPoint;
	int atkPoint;
	int maxHitPoint;
	int hitPoint;
	int speed;

	TextQuestCard(String name, int level, int conditionsPoint, int atkPoint, int maxHitPoint, int hitPoint, int speed){
		this.name = name;
		this.level = level;
		this.conditionsPoint = conditionsPoint;
		this.atkPoint = atkPoint;
		this.maxHitPoint = maxHitPoint;
		this.hitPoint = hitPoint;
		this.speed = speed;
	}
	
	/*回数は66回まで*/
	TextQuestCard adventure(TextQuestCard[] monster) {
		int random_adventure = (int)(Math.random()*100) + 1;
		if(1 <= random_adventure && random_adventure <= 10) {
			/*何もなかった*/
			this.hitPoint = this.hitPoint + (this.maxHitPoint*10)/100;
		}
		else if(11 <= random_adventure && random_adventure <= 100) {
			/*モンスターに出くわす*/
			if(this.level >= this.conditionsPoint) {
				int random_monster = (int)(Math.random() * (conditionsPoint + 1));
				return monster[random_monster];
			}
		}
		return null;
	}
	
	void printInfo() {
		System.out.println("[状態出力]");
		System.out.println(this.name);
		System.out.println("体力: " + this.hitPoint + " 攻撃力: " + this.atkPoint + " 素早さ: " + this.speed);
		
	}
}

public class TextQuest {
	public static void main(String[] args) {
		/*キャラクター*/
		
		TextQuestCard[] monster = new TextQuestCard[21];
		
		TextQuestCard player = new TextQuestCard("冒険者", 1, 0, 2, 5, 5, 3);
		TextQuestCard partner = new TextQuestCard("相棒", 1, 0, 3, 4, 4, 4);
		
		monster[0] = new TextQuestCard("オオカミ", 0, 1, 3, 2, 2, 5);
		monster[1] = new TextQuestCard("スライム",0,1,1,3,3,5);
		monster[2] = new TextQuestCard("グール",0,3,3,5,5,3);
		monster[3] = new TextQuestCard("ゴブリン",0,5,5,5,5,4);
		monster[4] = new TextQuestCard("コボルト",0,5,5,4,4,5);
		monster[5] = new TextQuestCard("クマ",0,10,8,10,10,7);
		monster[6] = new TextQuestCard("スケルトン",0,10,5,10,10,4);
		monster[7] = new TextQuestCard("オーク",0,15,10,15,15,6);
		monster[8] = new TextQuestCard("ゴーレム",0,15,10,40,40,5);
		monster[9] = new TextQuestCard("ミミック",0,15,15,20,20,10);
		monster[10] = new TextQuestCard("ドレイク",0,20,15,30,30,8);
		monster[11] = new TextQuestCard("トロール",0,20,15,40,40,5);
		monster[12] = new TextQuestCard("オーガ",0,25,20,50,50,8);
		monster[13] = new TextQuestCard("ドラゴン",0,25,20,40,40,10);
		monster[14] = new TextQuestCard("勇者",0,25,22,60,60,9);
		monster[15] = new TextQuestCard("グリフォン",0,26,23,55,55,12);
		monster[16] = new TextQuestCard("ケルベロス",0,26,25,60,60,10);
		monster[17] = new TextQuestCard("リッチ",0,27,25,70,70,8);
		monster[18] = new TextQuestCard("デュラハン",0,28,28,80,80,15);
		monster[19] = new TextQuestCard("雪の女王",0,28,30,65,65,12);
		monster[20] = new TextQuestCard("魔王",0,30,35,100,100,10);
		
		//player.sleep();
		player.printInfo();
		TextQuestCard across = player.adventure(monster);
		if (across == null) {
			System.out.println("今日は何も見つからなかった。");
		} else {
			System.out.println(across.name + "に出くわした！");
		}
	}
}