basic GUI structure implemented, along with -c or --cli flags to run in a CLI rather than launch the GUI.

src/App.java

@@ -0,0 +1,58 @@
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.UIManager;
+
+import java.awt.BorderLayout;
+import java.awt.Dimension;
+
+/**
+ * Runner class for the Sudoku App, managing the GUI and coordinating internal logic.
+ */
+public class App extends JFrame {
+    private Settings settings;
+
+    public App() {
+        super("Sudoku");
+        settings = new Settings();
+        initSetup();
+    }
+
+    /**
+     * Basic JFrame setup for the GUI.
+     */
+    private void initSetup() {
+        // TODO: These are just some default values, these should use the values from Settings.
+        setDefaultCloseOperation(EXIT_ON_CLOSE);
+        setLayout(new BorderLayout());
+        setPreferredSize(new Dimension(750, 550));
+        setSize(getPreferredSize());
+        setResizable(false);
+        setLocationRelativeTo(null);
+
+        try {
+            UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
+        } catch (Exception e) {
+            System.out.println("Error with cross platform look/feel in frameSetup().");
+        }
+    }
+
+    private JPanel createApp() {
+        // TODO: Create the root JPanel holding all other GUI components.
+
+        return null;
+    }
+
+    public static void cli() {
+        Nav nav = new Nav(new Settings());
+        SudokuChecker check = new SudokuChecker(nav.getLoadedGrid());
+    }
+
+    public static void main(String[] args) {
+        if(args.length == 0)
+            new App().setVisible(true);
+        else if(args[0].equals("-c") || args[0].equals("--cli"))
+            cli();
+        else
+            new App().setVisible(true);
+    }
+}

src/Nav.java

@@ -89,7 +89,7 @@ public class Nav extends JPanel {
      * @param String
      */
     private void openFile(String filename) {
-        File f = new File(/*"spring24/sudoku/" + */filename + ".sdku");
+        File f = new File("resources/" + filename + ".sdku");
         if(f == null || !f.exists() || f.isDirectory() || !f.canRead()) {
             System.out.println(
                     "The file " + filename + 

src/resources/input.sdku

@@ -0,0 +1,9 @@
+53..7....
+6..195...
+.98....6.
+8...6...3
+4..8.3..1
+7...2...6
+.6....28.
+...419..5
+....8..79

src/resources/master-difficulty.sdku

@@ -0,0 +1,9 @@
+.9...2.7.
+.....3..6
+..196..8.
+4......1.
+.....6...
+.3.75...8
+...2.....
+.7.89...5
+..3...7..

src/resources/test.sdku

@@ -0,0 +1,9 @@
+8.14.....
+.4.83...6
+6..5921.4
+27.1.9538
+...6..4.9
+59.3...7.
+.2.....65
+36.95..1.
+........3

src/run.ps1

@@ -1,3 +1,3 @@
 javac *.java
-java Sudoku
+java App -c
 rm *.class