implement xp/level logic

Java-Knight/src/main/java/org/project/entity/players/Player.java

@@ -1,6 +1,7 @@
 package org.project.entity.players;
 
 import org.project.entity.Entity;
+import org.project.entity.enemies.Dragon;
 import org.project.entity.enemies.Goblin;
 import org.project.entity.enemies.Skeleton;
 import org.project.item.armors.Armor;
@@ -26,6 +27,10 @@ public abstract class Player implements Entity, CombatOptions {
     private boolean hasVampireKey = false;
     private boolean successfulAction = true;
     private Consumable flask;
+    private int level = 1;
+    private int xp = 0;
+    private static final int BASE_XP = 50;
+    private static final double XP_SCALE = 1.4;
 
     public Player(String name, int hp, int mp, Weapon weapon, Armor armor) {
         this.name = name;
@@ -216,4 +221,40 @@ public abstract class Player implements Entity, CombatOptions {
         return flask;
     }
 
+    public int xpToNextLevel() {
+        return (int) (BASE_XP * Math.pow(XP_SCALE, level - 1));
+    }
+
+    private void levelUp() {
+        level++;
+        maxHP += 10;
+        maxMP += 8;
+        setHP(getHP() + 10);   // heal by the amount gained
+        setMP(getMP() + 8);
+        System.out.println("★ LEVEL UP! " + getClass().getSimpleName()
+                + " is now level " + level
+                + " | Max HP +" + 10 + " | Max MP +" + 8);
+    }
+
+    public void gainXP(int amount) {
+        xp += amount;
+        System.out.println(getClass().getSimpleName() + " gained " + amount + " XP! ("
+                + xp + "/" + xpToNextLevel() + ")");
+        while (xp >= xpToNextLevel()) {
+            xp -= xpToNextLevel();
+            levelUp();
+        }
+    }
+
+    public static int xpRewardFor(Entity enemy) {
+        if (enemy instanceof Dragon)   return 300;
+        if (enemy instanceof Goblin)   return 40;
+        if (enemy instanceof Skeleton) return 50;
+        return 60;
+    }
+
+    public int getLevel() { return level; }
+
+    public int getXP()    { return xp; }
+
 }