Boosters with the same multiplier now stack

src/main/java/net/Indyuce/mmocore/api/experience/Booster.java

@@ -4,11 +4,15 @@ import java.util.UUID;
 
 public class Booster {
 	private final UUID uuid = UUID.randomUUID();
-	private final long date = System.currentTimeMillis(), length;
+	private final long date = System.currentTimeMillis();
 	private final Profession profession;
 	private final double extra;
 	private final String author;
 
+	// length not final because boosters can stack, this allows to reduce the
+	// amount of boosters
+	private long length;
+
 	public Booster(double extra, long length) {
 		this(null, null, extra, length);
 	}
@@ -40,6 +44,10 @@ public class Booster {
 		return length;
 	}
 
+	public void addLength(long length) {
+		this.length += length;
+	}
+
 	public boolean hasProfession() {
 		return profession != null;
 	}
@@ -67,4 +75,8 @@ public class Booster {
 	public String getAuthor() {
 		return author;
 	}
+
+	public boolean canStackWith(Booster booster) {
+		return extra == booster.extra && (profession != null ? profession.equals(booster.getProfession()) : booster.getProfession() == null);
+	}
 }

src/main/java/net/Indyuce/mmocore/manager/social/BoosterManager.java

@@ -11,7 +11,16 @@ public class BoosterManager {
 	private List<Booster> map = new ArrayList<>();
 
 	public void register(Booster booster) {
+
+		// always flush booster list to reduce future calculations
 		flush();
+
+		for (Booster active : map)
+			if (active.canStackWith(booster)) {
+				active.addLength(booster.getLength());
+				return;
+			}
+
 		map.add(booster);
 	}
 
@@ -25,14 +34,17 @@ public class BoosterManager {
 
 	public int calculateExp(Profession profession, double exp) {
 		flush();
+
 		for (Booster booster : map)
 			if (booster.getProfession() == profession)
 				exp = booster.calculateExp(exp);
+
 		return (int) exp;
 	}
 
 	public List<Booster> getBoosters() {
 		flush();
+
 		return map;
 	}