Fixed structures like trees being able to grow outside border

src/main/java/com/songoda/skyblock/api/island/Island.java

@@ -502,4 +502,15 @@ public class Island {
 	public com.songoda.skyblock.island.Island getIsland() {
 		return handle;
 	}
+
+	@Override
+	public boolean equals(Object object) {
+		if (!(object instanceof Island))
+			return false;
+		Island other = (Island) object;
+		if (!other.getIslandUUID().equals(getIslandUUID()))
+			return false;
+		return true;
+	}
+
 }

src/main/java/com/songoda/skyblock/listeners/Grow.java

@@ -0,0 +1,51 @@
+package com.songoda.skyblock.listeners;
+
+import org.bukkit.block.BlockState;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.world.StructureGrowEvent;
+
+import com.songoda.skyblock.SkyBlock;
+import com.songoda.skyblock.island.Island;
+import com.songoda.skyblock.island.IslandManager;
+import com.songoda.skyblock.world.WorldManager;
+
+public class Grow implements Listener {
+
+	private final SkyBlock skyblock;
+
+	public Grow(SkyBlock skyblock) {
+		this.skyblock = skyblock;
+	}
+
+	/**
+	 * Checks that a structure like a tree is not growing outside or into another island.
+	 * @author LimeGlass
+	 */
+	@EventHandler
+	public void onStructureGrow(StructureGrowEvent event) {
+		WorldManager worldManager = skyblock.getWorldManager();
+		if (!worldManager.isIslandWorld(event.getWorld()))
+			return;
+
+		IslandManager islandManager = skyblock.getIslandManager();
+		Island origin = islandManager.getIslandAtLocation(event.getLocation());
+		for (BlockState state : event.getBlocks()) {
+			Island growingTo = islandManager.getIslandAtLocation(state.getLocation());
+			// This block is ok to continue as it's not related to Skyblock islands.
+			if (origin == null && growingTo == null)
+				continue;
+			// A block from the structure is outside/inside that it's not suppose to.
+			if (origin == null || growingTo == null) {
+				event.getBlocks().remove(state);
+				continue;
+			}
+			// The structure is growing from one island to another.
+			if (!origin.getIslandUUID().equals(growingTo.getIslandUUID())) {
+				event.getBlocks().remove(state);
+				continue;
+			}
+		}
+	}
+
+}