private static void onePlayer(int numOfCards) {
		frame.setLayout(new BorderLayout());
		// If a game has already been started
		// cardHolderPanel has to be cleared before
		// it can be used properly again.
		cardHolderPanel.removeAll();
		
		// Adds the cardHolderPanel to the frame.
		frame.add(cardHolderPanel, BorderLayout.CENTER);
		
		// The user is asked for his/her name. If "null" is given as name, a 
		// new pop up window will appear and ask for the player's name again.
		// If cancel is pressed, null is returned and this method is ended.
		String playerName = JOptionPane.showInputDialog("What is your name?");
		if (playerName == null) {
			return;
		}
		while (playerName.equals("null")) {
			playerName = JOptionPane
					.showInputDialog("Not valid name. \n What is your name?");
			if (playerName == null) {
				return;
			}
		}
		
		// A new playerHolder with only one player. "null" is a player never used.
		PlayerHolder players = new PlayerHolder(playerName, "null");
		
		// A new cardHolder is created and with it all the cards, actionListeners
		// and the game is started.
		new CardHolder(numOfCards, players, cardHolderPanel);
		
		// Updates the cardHolderPanel and sets it visible
		cardHolderPanel.updateUI();
		backgroundPanel.setVisible(false);
		cardHolderPanel.setVisible(true);
		
	}