Java: Connect 4 Diagonal Win

Forgive me for not answering this question directly, but this is stuff that will help you fix it and get better code and better code writing in the future.

Extracting the logic of your if condition into a separate method makes it easier to think about that logic yourself and allows you to test it independently of the rest of the program.

So instead of:

  if (board[x][y] == 1 && board[x - 1][y - 1] == 1 && board[x - 2][y - 2] == 1 && board[x - 3][y - 3] == 1) {
       JOptionPane.showMessageDialog(...)
  }

      

        
        
        
      

    

... use:

 if(isDiagonalLeft(x,y,1) { ... }

      

        
        
        
      

    

... and ...

 boolean isDiagonalLeft(int x, int y, int player) {
      return board[x][y] == player && 
             board[x - 1][y - 1] == player  && 
             board[x - 2][y - 2] == player  && 
             board[x - 3][y - 3] == player 
 }

      

        
        
        
      

    

Now you can run unit tests on isDiagonalLeft () to make sure it works. That is, the little program that sets up the board and runs it, isDiagonalLeft (), to make sure it gives the right answer under various circumstances. It looks like extra work, but most people who try to find out are that it saves effort by catching mistakes earlier.

What you did was to separate the game logic somewhat from the presentation code (JOptionPane) so that the presentation code isn't the same when you just want to use the game logic. Later in your programming studies, you will come across the possibility of separating them even more, for example the Model-View-Controller model.

Pulling logic also helps if you need to ask questions about stack overflows - by separating game logic from Swing, you open the question to potential responders who know nothing about Swing.

And you can reuse this method once for each player, rather than copying the logic into two places like you do.

If that doesn't work, use the debugger in your IDE to step through it.

Now that you've done that, you can improve on this method so that the computer does the decrement instead of the programmer ...

  boolean isDiagonalLeft(int x, int y, int player) {
       for(int i = 0; i<4; i++) {
           if(board[x-i][y-i] != player) {
               return false;
           }
       }
       return true;
  }

      

        
        
        
      

    

... and you can generalize it to cover both directions of the diagonal:

  boolean isDiagonal(int x, int y, int player, boolean direction) {
       int dirUnit = direction ? -1 : 1;
       for(int i = 0; i<4; i++) {
           if(board[x-i][y + dirUnit] != player) {
               return false;
           }
       }
       return true;
  }

      

        
        
        
      

    

... so you can now reuse the method in 4 places; for every player and for every direction.

When you come across a situation where it doesn't work in your GUI, run unit tests that install the board as it is in the GUI and run on it isDiagonal()

. If the test passes, you know the problem is somewhere else. If the test fails, you can work with the debugger and method code to make it pass.