Add gc() function to force garbage collection

src/main/java/de/pickshadow/plugin/Main.java

@@ -62,7 +62,7 @@ public final class Main extends JavaPlugin {
         preinitialized = true;
     }
 
-    // Initialize classes requiring Bukkit API + initialize plugin
+    // Initialize plugin
     @Override
     public void onEnable() {
         if (failed || !preinitialized) {

src/main/java/de/pickshadow/plugin/commands/PluginCommand.java

@@ -69,7 +69,7 @@ public class PluginCommand extends CommandBase {
                 break;
             case "gc":
                 sender.sendMessage(Miscellaneous.format(Translation.PLUGINCOMMAND_GARBAGECOLLECT));
-                System.gc();
+                Miscellaneous.gc();
                 break;
             case "playerinfo":
                 if (sender instanceof ConsoleCommandSender) {

src/main/java/de/pickshadow/plugin/utils/Miscellaneous.java

@@ -26,6 +26,7 @@ import net.kyori.adventure.text.minimessage.MiniMessage;
 import org.bukkit.Bukkit;
 import org.jetbrains.annotations.NotNull;
 
+import java.lang.ref.WeakReference;
 import java.text.DecimalFormat;
 import java.util.Objects;
 
@@ -48,6 +49,18 @@ public class Miscellaneous {
         }
     }
 
+    // Ensures garbage collection
+    // Stolen from JLibs
+    // https://github.com/santhosh-tekuri/jlibs/blob/e001fb7286c84f456125d1be00fc9a7e3b128881/core/src/main/java/jlibs/core/lang/RuntimeUtil.java#L148
+    public static void gc(){
+        ObjHolder.logger.warn(Miscellaneous.class, "Forcing garbage collection");
+        Object obj = new Object();
+        WeakReference<Object> ref = new WeakReference<>(obj);
+        obj = null;
+        while(ref.get() != null)
+            System.gc();
+    }
+
     // Data type conversion
     /// Bytes <-> Mebibytes
     public static double byteToMib(int bytes, boolean flatten) {