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As one can see from the above examples of Tic-Tac-Toe code, the algorithm code is intertwined with low-level game board implementation details. This not only obscures the essence of the solution, but also makes it impossible to re-use in different types of games. What essentially “throw"throw-away” away" code.
To remedy this situation, we seek to design an OO model for two-person games that enables us to express all facets of the games at the highest level of abstraction. The result is a system of cooperating objects that possesses many of the essential qualities in software engineering: correctness, robustness, extensibility, flexibility, and reusability. The demo program below shows the what an OO game model can do.
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/** This class represents an abstract player of the game.
* The players are represented as a circular linked list.
*/
public abstract class APlayer {
private IRequestor requestor;
private int player;
private APlayer nextPlayer = this;
/** The constructor for the class.
* @param requestor The requestor that the player uses to request moves of the board.
* @param player The player number of this player.
*/
public APlayer(IRequestor requestor, int player) {
this.requestor = requestor;
this.player = player;
}
/** Tells this player to take its turn. */
public abstract void takeTurn();
/** other methods elided... */
}
/* This class represents a concrete computer player. */
public class ComputerPlayer extends APlayer {
private INextMoveStrategy nextMoveStrategy;
private IModel model;
/** The constructor for the class.
* @param requestor The requestor that this player will use to communicate with the model.
* @param player This player's player number.
* @param model A reference to the IModel. Needed to call the getNextMove() method
* of the INextMoveStrategy.
* @param nextMoveStrategy The strategy used to calculate this player's next move.
*/
public ComputerPlayer(IRequestor requestor, int player, IModel model, INextMoveStrategy nextMoveStrategy) {
super(requestor, player);
this.model = model;
this.nextMoveStrategy = nextMoveStrategy;
System.out.println("ComputerPlayer is using " + nextMoveStrategy);
}
/** Used by the TurnControl to tell this player to take its turn.
* When the computer takes its turn, it will calculate its next move and
* then request that move of the model.
* If the computer makes and invalid move, the computer will print an error
* message to the screen and then it will take its turn again.
*/
public void takeTurn() {
System.out.print("Computer player "+ getPlayer() +" ("+ this +") takes turn...");
final Point p = nextMoveStrategy.getNextMove(model, getPlayer());
System.out.println("and moves to "+ p);
getRequestor().setTokenAt (p.y, p.x, getPlayer(), new IRejectCommand() {
// ANONYMOUS COMMAND!
public void execute() {
System.out.println("ComputerPlayer: The move at ("+p.x+", "+p.y+") is invalid.");
takeTurn();
}
});
}
}
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When a player is instantiated, it is given an IRequestor to communicate with the model. As shown in ComputerPlayer.takeTurn() , the computer player gets the best next move from the next move strategy and then asks the requestor ( getRequestor() ) to set the game token at the best move's position, passing to the requestor an anonymous IRejectCommand , in case the move is illegal. This situation may happen if the next move strategy is a totally random move.
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In this lab you are to work with others to try to implement the IRequestor anonymous inner class that is stubbed out the GameModel code. This is part of the upcoming homework 11.
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Download and extract the file hw11_12.zip . You should see the following files.
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src : a subdirectory containing the source code of the Games program with a few stubbed out code for you to complete.
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games.xml : a DrJava project file
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<li> P4M2.jar : the Java binary code of the game framework.
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tttboard.jar : the Java binary code for the Tic-Tac-Toe gameboard.
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Use DrJava to open the games.xml project file. Compile and run the project. You will discover that you cannot do much because the code for the Tic-Tac-Toe board ( model.board.TicTacToe.java=) and =model.GameModel.java have been stubbed out.
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Open the Project Properties dialog and add P4M2.jar and tttboard.jar to the Extra Class Path. Now compile and run the project. Both the Tic-Tac-Toe game and the Othello game should work.
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Now open the Project Properties dialog and remove P4M2.jar from the Extra Class Path. Open the file model.GameModel.java and edit the code for the anonymous inner class IRequestor to make the game program work again. Hint: review the documentation for IBoardModel , TurnControl and IViewAdmin . Click here for the complete Javadoc specification of the game framework.
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