Use threading for AI

src/Board.java

@@ -25,6 +25,7 @@ public class Board {
     King whiteKing;
     final DrawingPanel panel;
     final Graphics graphics;
+    public boolean aiThinking = false;
 
     // The board is a two-dimensional array of nullable pieces
     Piece[][] board;
@@ -170,6 +171,7 @@ public class Board {
             setup();
             return;
         }
+        if (aiThinking) return;
         // Get board coordinate of mouse click
         BoardCoordinate coordinate = new ScreenCoordinate(x, y).toBoard();
         // If there's no piece there, return
@@ -199,12 +201,18 @@ public class Board {
                     move(legalMove);
                     setLastMovedPieceAsMoved();
                     checkForCheckmate();
+                    // Clear dragging
+                    dragging = null;
+                    // Redraw without dragging
+                    draw();
                     if (!isGameOver) {
-                        move(ChessAI.findBestMove(this));
-                        setLastMovedPieceAsMoved();
-                        checkForCheckmate();
+                        try {
+                            ChessAI.move(this);
+                        } catch (Exception e) {
+                            System.out.println(e);
+                        }
+                        return;
                     }
-                    break;
                 }
             }
         }

src/ChessAI.java

@@ -1,9 +1,32 @@
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Future;
+import java.util.concurrent.FutureTask;
 
 public class ChessAI {
     private static final int MAX_DEPTH = 3;
 
+    public static FutureTask<Void> move(Board board) {
+        Callable<Void> callable = new Callable<>() {
+            @Override
+            public Void call() throws Exception {
+                board.aiThinking = true;
+                Move move = findBestMove(board);
+                board.move(move);
+                board.setLastMovedPieceAsMoved();
+                board.checkForCheckmate();
+                board.draw();
+                board.aiThinking = false;
+                return null;
+            }
+        };
+        FutureTask<Void> future = new FutureTask<>(callable);
+        Thread thread = new Thread(future);
+        thread.start();
+        return future;
+    }
+
     public static Move findBestMove(Board board) {
         int bestScore = Integer.MIN_VALUE;