Changed start method name to getInstance.

src/main/java/gui/src/ViewThread.java

@@ -10,7 +10,7 @@ public class ViewThread extends Thread implements View {
     private static final String className = "ViewThread";
 
     public void run() {
-        MainFrame.start();
+        MainFrame.getInstance();
         printMessage("Swing ui thread was started.");
     }
 

src/main/java/gui/src/frames/MainFrame.java

@@ -39,7 +39,7 @@ public final class MainFrame extends JFrame implements Themeable {
         this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     }
 
-    public static MainFrame start() {
+    public static MainFrame getInstance() {
         if (null == instance) {
             instance = new MainFrame();
         }