removed singleton inheritance and re implemented with thread safe

Main/src/main/java/Classes/MetaClass/Singleton.java

@@ -1,9 +0,0 @@
-package Classes.MetaClass;
-
-public class Singleton {
-    private static Singleton single_instance = new Singleton();
-
-     public static Singleton getInstance(){
-         return single_instance;
-    }
-}

Main/src/main/java/Classes/SettingsManager.java

@@ -1,29 +1,38 @@
 package Classes;
-
-import Classes.MetaClass.Singleton;
 import Objects.*;
 import org.json.JSONObject;
 
 import java.util.HashMap;
 
-public class SettingsManager extends Singleton  {
-    public static int x = 5; // example of how to setup variable in singleton
+public class SettingsManager  {
+    private static SettingsManager instance;
+    private SettingsManager() {
+        InitiateGeneralSettings();
+        InitiateCamerasInfo();
+        InitiateUsbCameras();
+        InitiateUsbCamerasSettings();
+    }
+    public static synchronized SettingsManager getInstance(){
+        if(instance == null){
+            synchronized (SettingsManager.class) {
+                if(instance == null){
+                    instance = new SettingsManager();
+                }
+            }
+        }
+        return instance;
+    }
     public static HashMap cams = new HashMap();
     public static HashMap UsbCameras = new HashMap();
     public static HashMap USBCamerasInfo = new HashMap();
     public static DefaultGeneralSettings GeneralSettings;
     public static HashMap CameraPort = new HashMap();
     public static HashMap CamerasCurrentPipeline = new HashMap();
-    public SettingsManager(){
-        InitiateGeneralSettings();
-        InitiateCamerasInfo();
-        InitiateUsbCameras();
-        InitiateUsbCamerasSettings();
-    }
 
     private void InitiateGeneralSettings(){
-
+        System.out.println("run");
     }
+
     private void InitiateCamerasInfo(){
 
     }

Main/src/main/java/Main.java

@@ -2,7 +2,7 @@ import Classes.SettingsManager;
 import Handlers.Web.Server;
 public class Main {
     public static void main(String [] args) {
-        SettingsManager Manager = new SettingsManager();
+        SettingsManager manager = SettingsManager.getInstance();
         Server.main(8888);
     }
 }