Step 4

Overview

In this step you will set up the response to "Start New Game" button clicks. This will only involve changes in the TicTacToe class. You will need to change the initialization of the toPlay instance variable, add getCell() and startNewGame() methods, and registering a listener for the "Start New Game" button.

Changing the Initialization of toPlay

Change the initialization on the toPlay variable from TTTCell.X to TTTCell.NO_ONE. Due to the fact that the makePlay() method was designed to do nothing when toPlay is TTTCell.NO_ONE, this change prevents the user from changing marks when the applet starts up. Changes made in later sections of this step will change toPlay to TTTCell.X when the "Start New Game" button is clicked, allowing the user to proceed.

The getCell() Method

This method is a convenience method that keeps ugly code from appearing in a number of different places. It returns a TTTCell and has an int parameter n. It contains just one not very pretty statement. 
    return (TTTCell)board.getComponent(n);

When the 9 cells were added to the board, they were assigned numbers from 0 to 8. They are retrieved using the getComponent() method, defined in the old AWT Component class. The parameter specifies the assigned cell number.

The getCell() method makes it easier to do something with all of the cells. You just write a for loop like the following. 

    for (int i = 0; i < 9; i++) {
	TTTCell c = getCell(i);
	do something with c
    }
You will need loops like this in several places. The first will be in the next section.

The startNewGame() Method

This method will be invoked in the button listener described in the next section. It has no parameters and no returned value. It begins with a for loop to step through all of the cells in the game board (use getCell()), sending a setMark(TTTCell.NO_ONE) message to each. This clears the marks from all of the cells.

After the loop, set the toPlay instance variable to TTTCell.X. This makes X the first player for the new game and allows the user to make X marks in the cells.

Adding a Listener for the "Start New Game" Button

The only remaining change is adding an action listener to the startNewGameButton instance variable. This listener should be added in the init() method. The listener's actionPerformed() method should just invoke your startNewGame() method.

After you have made the above changes, recompile your TTTCell class and run the applet with appletviewer. You should see two changes in the behavior of the applet. First, nothing will happen when you click on a cell until you have clicked on the "Start New Game" button. After that, X marks will appear in cells that you click on, as before. The second change is that all of the marks will be cleared whenever you click on the "Start New Game" button.

Demonstration Applet