J2ME Game: Maze Game


Title: J2ME Games With MIDP2
Authors: Carol Hamer
Publisher: Apress
ISBN: 1590593820
*/



import java.util.Random;
import java.util.Vector;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

/**
* This is the main class of the maze game.
*
* @author Carol Hamer
*/
public class Maze extends MIDlet implements CommandListener {

//----------------------------------------------------------------
// game object fields

/**
* The canvas that the maze is drawn on.
*/
private MazeCanvas myCanvas;

/**
* The screen that allows the user to alter the size parameters
* of the maze.
*/
private SelectScreen mySelectScreen;

//----------------------------------------------------------------
// command fields

/**
* The button to exit the game.
*/
private Command myExitCommand = new Command("Exit", Command.EXIT, 99);

/**
* The command to create a new maze. (This command may appear in a menu)
*/
private Command myNewCommand = new Command("New Maze", Command.SCREEN, 1);

/**
* The command to dismiss an alert error message. In MIDP 2.0
* an Alert set to Alert.FOREVER automatically has a default
* dismiss command. This program does not use it in order to
* allow backwards com
*/
private Command myAlertDoneCommand = new Command("Done", Command.EXIT, 1);

/**
* The command to go to the screen that allows the user
* to alter the size parameters. (This command may appear in a menu)
*/
private Command myPrefsCommand
= new Command("Size Preferences", Command.SCREEN, 1);

//----------------------------------------------------------------
// initialization

/**
* Initialize the canvas and the commands.
*/
public Maze() {
try {
myCanvas = new MazeCanvas(Display.getDisplay(this));
myCanvas.addCommand(myExitCommand);
myCanvas.addCommand(myNewCommand);
myCanvas.addCommand(myPrefsCommand);
myCanvas.setCommandListener(this);
} catch(Exception e) {
// if there's an error during creation, display it as an alert.
Alert errorAlert = new Alert("error",
e.getMessage(), null, AlertType.ERROR);
errorAlert.setCommandListener(this);
errorAlert.setTimeout(Alert.FOREVER);
errorAlert.addCommand(myAlertDoneCommand);
Display.getDisplay(this).setCurrent(errorAlert);
}
}

//----------------------------------------------------------------
// implementation of MIDlet

/**
* Start the application.
*/
public void startApp() throws MIDletStateChangeException {
if(myCanvas != null) {
myCanvas.start();
}
}

/**
* Clean up.
*/
public void destroyApp(boolean unconditional)
throws MIDletStateChangeException {
myCanvas = null;
System.gc();
}

/**
* Does nothing since this program occupies no shared resources
* and little memory.
*/
public void pauseApp() {
}

//----------------------------------------------------------------
// implementation of CommandListener

/*
* Respond to a command issued on the Canvas.
* (reset, exit, or change size prefs).
*/
public void commandAction(Command c, Displayable s) {
if(c == myNewCommand) {
myCanvas.newMaze();
} else if(c == myAlertDoneCommand) {
try {
destroyApp(false);
notifyDestroyed();
} catch (MIDletStateChangeException ex) {
}
} else if(c == myPrefsCommand) {
if(mySelectScreen == null) {
mySelectScreen = new SelectScreen(myCanvas);
}
Display.getDisplay(this).setCurrent(mySelectScreen);
} else if(c == myExitCommand) {
try {
destroyApp(false);
notifyDestroyed();
} catch (MIDletStateChangeException ex) {
}
}
}

}



/**
* This class is the display of the game.
*
* @author Carol Hamer
*/
class MazeCanvas extends javax.microedition.lcdui.Canvas {

//---------------------------------------------------------
// static fields

/**
* color constant
*/
public static final int BLACK = 0;

/**
* color constant
*/
public static final int WHITE = 0xffffff;

//---------------------------------------------------------
// instance fields

/**
* a handle to the display.
*/
private Display myDisplay;

/**
* The data object that describes the maze configuration.
*/
private Grid myGrid;

/**
* Whether or not the currently displayed maze has
* been completed.
*/
private boolean myGameOver = false;

/**
* maze dimension: the width of the maze walls.
*/
private int mySquareSize;

/**
* maze dimension: the maximum width possible for the maze walls.
*/
private int myMaxSquareSize;

/**
* maze dimension: the minimum width possible for the maze walls.
*/
private int myMinSquareSize;

/**
* top corner of the display: x-coordiate
*/
private int myStartX = 0;

/**
* top corner of the display: y-coordinate
*/
private int myStartY = 0;

/**
* how many rows the display is divided into.
*/
private int myGridHeight;

/**
* how many columns the display is divided into.
*/
private int myGridWidth;

/**
* the maximum number columns the display can be divided into.
*/
private int myMaxGridWidth;

/**
* the minimum number columns the display can be divided into.
*/
private int myMinGridWidth;

/**
* previous location of the player in the maze: x-coordiate
* (in terms of the coordinates of the maze grid, NOT in terms
* of the coordinate system of the Canvas.)
*/
private int myOldX = 1;

/**
* previous location of the player in the maze: y-coordinate
* (in terms of the coordinates of the maze grid, NOT in terms
* of the coordinate system of the Canvas.)
*/
private int myOldY = 1;

/**
* current location of the player in the maze: x-coordiate
* (in terms of the coordinates of the maze grid, NOT in terms
* of the coordinate system of the Canvas.)
*/
private int myPlayerX = 1;

/**
* current location of the player in the maze: y-coordinate
* (in terms of the coordinates of the maze grid, NOT in terms
* of the coordinate system of the Canvas.)
*/
private int myPlayerY = 1;

//-----------------------------------------------------
// gets / sets

/**
* Changes the width of the maze walls and calculates how
* this change affects the number of rows and columns
* the maze can have.
* @return the number of columns now that the the
* width of the columns has been updated.
*/
int setColWidth(int colWidth) {
if(colWidth < 2) { mySquareSize = 2; } else { mySquareSize = colWidth; } myGridWidth = getWidth() / mySquareSize; if(myGridWidth % 2 == 0) { myGridWidth -= 1; } myGridHeight = getHeight() / mySquareSize; if(myGridHeight % 2 == 0) { myGridHeight -= 1; } myGrid = null; return(myGridWidth); } /** * @return the minimum width possible for the maze walls. */ int getMinColWidth() { return(myMinSquareSize); } /** * @return the maximum width possible for the maze walls. */ int getMaxColWidth() { return(myMaxSquareSize); } /** * @return the maximum number of columns the display can be divided into. */ int getMaxNumCols() { return(myMaxGridWidth); } /** * @return the width of the maze walls. */ int getColWidth() { return(mySquareSize); } /** * @return the number of maze columns the display is divided into. */ int getNumCols() { return(myGridWidth); } //----------------------------------------------------- // initialization and game state changes /** * Constructor performs size calculations. * @throws Exception if the display size is too * small to make a maze. */ public MazeCanvas(Display d) throws Exception { myDisplay = d; // a few calculations to make the right maze // for the current display. int width = getWidth(); int height = getHeight(); // tests indicate that 5 is a good default square size, // but the user can change it... mySquareSize = 5; myMinSquareSize = 3; myMaxGridWidth = width / myMinSquareSize; if(myMaxGridWidth % 2 == 0) { myMaxGridWidth -= 1; } myGridWidth = width / mySquareSize; if(myGridWidth % 2 == 0) { myGridWidth -= 1; } myGridHeight = height / mySquareSize; if(myGridHeight % 2 == 0) { myGridHeight -= 1; } myMinGridWidth = 15; myMaxSquareSize = width / myMinGridWidth; if(myMaxSquareSize > height / myMinGridWidth) {
myMaxSquareSize = height / myMinGridWidth;
}
// if the display is too small to make a reasonable maze,
// then we throw an Exception
if(myMaxSquareSize < mySquareSize) { throw(new Exception("Display too small")); } } /** * This is called as soon as the application begins. */ void start() { myDisplay.setCurrent(this); repaint(); } /** * discard the current maze and draw a new one. */ void newMaze() { myGameOver = false; // throw away the current maze. myGrid = null; // set the player back to the beginning of the maze. myPlayerX = 1; myPlayerY = 1; myOldX = 1; myOldY = 1; myDisplay.setCurrent(this); // paint the new maze repaint(); } //------------------------------------------------------- // graphics methods /** * Create and display a maze if necessary, otherwise just * move the player. Since the motion in this game is * very simple, it is not necessary to repaint the whole * maze each time, just the player + erase the square * that the player just left.. */ protected void paint(Graphics g) { // If there is no current maze, create one and draw it. if(myGrid == null) { int width = getWidth(); int height = getHeight(); // create the underlying data of the maze. myGrid = new Grid(myGridWidth, myGridHeight); // draw the maze: // loop through the grid data and color each square the // right color for(int i = 0; i < myGridWidth; i++) { for(int j = 0; j < myGridHeight; j++) { if(myGrid.mySquares[i][j] == 0) { g.setColor(BLACK); } else { g.setColor(WHITE); } // fill the square with the appropriate color g.fillRect(myStartX + (i*mySquareSize), myStartY + (j*mySquareSize), mySquareSize, mySquareSize); } } // fill the extra space outside of the maze g.setColor(BLACK); g.fillRect(myStartX + ((myGridWidth-1) * mySquareSize), myStartY, width, height); // erase the exit path: g.setColor(WHITE); g.fillRect(myStartX + ((myGridWidth-1) * mySquareSize), myStartY + ((myGridHeight-2) * mySquareSize), width, height); // fill the extra space outside of the maze g.setColor(BLACK); g.fillRect(myStartX, myStartY + ((myGridHeight-1) * mySquareSize), width, height); } // draw the player (red): g.setColor(255, 0, 0); g.fillRoundRect(myStartX + (mySquareSize)*myPlayerX, myStartY + (mySquareSize)*myPlayerY, mySquareSize, mySquareSize, mySquareSize, mySquareSize); // erase the previous location if((myOldX != myPlayerX) || (myOldY != myPlayerY)) { g.setColor(WHITE); g.fillRect(myStartX + (mySquareSize)*myOldX, myStartY + (mySquareSize)*myOldY, mySquareSize, mySquareSize); } // if the player has reached the end of the maze, // we display the end message. if(myGameOver) { // perform some calculations to place the text correctly: int width = getWidth(); int height = getHeight(); Font font = g.getFont(); int fontHeight = font.getHeight(); int fontWidth = font.stringWidth("Maze Completed"); g.setColor(WHITE); g.fillRect((width - fontWidth)/2, (height - fontHeight)/2, fontWidth + 2, fontHeight); // write in red g.setColor(255, 0, 0); g.setFont(font); g.drawString("Maze Completed", (width - fontWidth)/2, (height - fontHeight)/2, g.TOP|g.LEFT); } } /** * Move the player. */ public void keyPressed(int keyCode) { if(! myGameOver) { int action = getGameAction(keyCode); switch (action) { case LEFT: if((myGrid.mySquares[myPlayerX-1][myPlayerY] == 1) && (myPlayerX != 1)) { myOldX = myPlayerX; myOldY = myPlayerY; myPlayerX -= 2; repaint(); } break; case RIGHT: if(myGrid.mySquares[myPlayerX+1][myPlayerY] == 1) { myOldX = myPlayerX; myOldY = myPlayerY; myPlayerX += 2; repaint(); } else if((myPlayerX == myGrid.mySquares.length - 2) && (myPlayerY == myGrid.mySquares[0].length - 2)) { myOldX = myPlayerX; myOldY = myPlayerY; myPlayerX += 2; myGameOver = true; repaint(); } break; case UP: if(myGrid.mySquares[myPlayerX][myPlayerY-1] == 1) { myOldX = myPlayerX; myOldY = myPlayerY; myPlayerY -= 2; repaint(); } break; case DOWN: if(myGrid.mySquares[myPlayerX][myPlayerY+1] == 1) { myOldX = myPlayerX; myOldY = myPlayerY; myPlayerY += 2; repaint(); } break; } } } } /** * This is the screen that allows the user to modify the * width of the maze walls.. * * @author Carol Hamer */ class SelectScreen extends Form implements ItemStateListener, CommandListener { //---------------------------------------------------------------- // fields /** * The "Done" button to exit this screen and return to the maze. */ private Command myExitCommand = new Command("Done", Command.EXIT, 1); /** * The gague that modifies the width of the maze walls. */ private Gauge myWidthGauge; /** * The gague that displays the number of columns of the maze. */ private Gauge myColumnsGauge; /** * A handle to the main game canvas. */ private MazeCanvas myCanvas; //---------------------------------------------------------------- // initialization /** * Create the gagues and place them on the screen. */ public SelectScreen(MazeCanvas canvas) { super("Size Preferences"); addCommand(myExitCommand); setCommandListener(this); myCanvas = canvas; setItemStateListener(this); myWidthGauge = new Gauge("Column Width", true, myCanvas.getMaxColWidth(), myCanvas.getColWidth()); myColumnsGauge = new Gauge("Number of Columns", false, myCanvas.getMaxNumCols(), myCanvas.getNumCols()); // Warning: the setLayout method does not exist in // MIDP 1.4. If there is any chance that a target // device will be using MIDP 1.4, comment out the // following two lines: //myWidthGauge.setLayout(Item.LAYOUT_CENTER); //myColumnsGauge.setLayout(Item.LAYOUT_CENTER); append(myWidthGauge); append(myColumnsGauge); } //---------------------------------------------------------------- // implementation of ItemStateListener /** * Respond to the user changing the width. */ public void itemStateChanged(Item item) { if(item == myWidthGauge) { int val = myWidthGauge.getValue(); if(val < myCanvas.getMinColWidth()) { myWidthGauge.setValue(myCanvas.getMinColWidth()); } else { int numCols = myCanvas.setColWidth(val); myColumnsGauge.setValue(numCols); } } } //---------------------------------------------------------------- // implementation of CommandListener /* * Respond to a command issued on this screen. * (either reset or exit). */ public void commandAction(Command c, Displayable s) { if(c == myExitCommand) { myCanvas.newMaze(); } } } /** * This class contains the data necessary to draw the maze. * * @author Carol Hamer */ class Grid { /** * Random number generator to create a random maze. */ private Random myRandom = new Random(); /** * data for which squares are filled and which are blank. * 0 = black * 1 = white * values higher than 1 are used during the maze creation * algorithm. * 2 = the square could possibly be appended to the maze this round. * 3 = the square's color is not yet decided, and the square is * not close enough to be appended to the maze this round. */ int[][] mySquares; //-------------------------------------------------------- // maze generation methods /** * Create a new maze. */ public Grid(int width, int height) { mySquares = new int[width][height]; // initialize all of the squares to white except a lattice // framework of black squares. for(int i = 1; i < width - 1; i++) { for(int j = 1; j < height - 1; j++) { if((i % 2 == 1) || (j % 2 == 1)) { mySquares[i][j] = 1; } } } // the entrance to the maze is at (0,1). mySquares[0][1] = 1; createMaze(); } /** * This method randomly generates the maze. */ private void createMaze() { // create an initial framework of black squares. for(int i = 1; i < mySquares.length - 1; i++) { for(int j = 1; j < mySquares[i].length - 1; j++) { if((i + j) % 2 == 1) { mySquares[i][j] = 0; } } } // initialize the squares that can be either black or white // depending on the maze. // first we set the value to 3 which means undecided. for(int i = 1; i < mySquares.length - 1; i+=2) { for(int j = 1; j < mySquares[i].length - 1; j+=2) { mySquares[i][j] = 3; } } // Then those squares that can be selected to be open // (white) paths are given the value of 2. // We randomly select the square where the tree of maze // paths will begin. The maze is generated starting from // this initial square and branches out from here in all // directions to fill the maze grid. Vector possibleSquares = new Vector(mySquares.length * mySquares[0].length); int[] startSquare = new int[2]; startSquare[0] = getRandomInt(mySquares.length / 2)*2 + 1; startSquare[1] = getRandomInt(mySquares[0].length / 2)*2 + 1; mySquares[startSquare[0]][startSquare[1]] = 2; possibleSquares.addElement(startSquare); // Here we loop to select squares one by one to append to // the maze pathway tree. while(possibleSquares.size() > 0) {
// the next square to be joined on is selected randomly.
int chosenIndex = getRandomInt(possibleSquares.size());
int[] chosenSquare = (int[])possibleSquares.elementAt(chosenIndex);
// we set the chosen square to white and then
// remove it from the list of possibleSquares (i.e. squares
// that can possibly be added to the maze), and we link
// the new square to the maze.
mySquares[chosenSquare[0]][chosenSquare[1]] = 1;
possibleSquares.removeElementAt(chosenIndex);
link(chosenSquare, possibleSquares);
}
// now that the maze has been completely generated, we
// throw away the objects that were created during the
// maze creation algorithm and reclaim the memory.
possibleSquares = null;
System.gc();
}

/**
* internal to createMaze. Checks the four squares surrounding
* the chosen square. Of those that are already connected to
* the maze, one is randomly selected to be joined to the
* current square (to attach the current square to the
* growing maze). Those squares that were not previously in
* a position to be joined to the maze are added to the list
* of "possible" squares (that could be chosen to be attached
* to the maze in the next round).
*/
private void link(int[] chosenSquare, Vector possibleSquares) {
int linkCount = 0;
int i = chosenSquare[0];
int j = chosenSquare[1];
int[] links = new int[8];
if(i >= 3) {
if(mySquares[i - 2][j] == 1) {
links[2*linkCount] = i - 1;
links[2*linkCount + 1] = j;
linkCount++;
} else if(mySquares[i - 2][j] == 3) {
mySquares[i - 2][j] = 2;
int[] newSquare = new int[2];
newSquare[0] = i - 2;
newSquare[1] = j;
possibleSquares.addElement(newSquare);
}
}
if(j + 3 <= mySquares[i].length) { if(mySquares[i][j + 2] == 3) { mySquares[i][j + 2] = 2; int[] newSquare = new int[2]; newSquare[0] = i; newSquare[1] = j + 2; possibleSquares.addElement(newSquare); } else if(mySquares[i][j + 2] == 1) { links[2*linkCount] = i; links[2*linkCount + 1] = j + 1; linkCount++; } } if(j >= 3) {
if(mySquares[i][j - 2] == 3) {
mySquares[i][j - 2] = 2;
int[] newSquare = new int[2];
newSquare[0] = i;
newSquare[1] = j - 2;
possibleSquares.addElement(newSquare);
} else if(mySquares[i][j - 2] == 1) {
links[2*linkCount] = i;
links[2*linkCount + 1] = j - 1;
linkCount++;
}
}
if(i + 3 <= mySquares.length) { if(mySquares[i + 2][j] == 3) { mySquares[i + 2][j] = 2; int[] newSquare = new int[2]; newSquare[0] = i + 2; newSquare[1] = j; possibleSquares.addElement(newSquare); } else if(mySquares[i + 2][j] == 1) { links[2*linkCount] = i + 1; links[2*linkCount + 1] = j; linkCount++; } } if(linkCount > 0) {
int linkChoice = getRandomInt(linkCount);
int linkX = links[2*linkChoice];
int linkY = links[2*linkChoice + 1];
mySquares[linkX][linkY] = 1;
int[] removeSquare = new int[2];
removeSquare[0] = linkX;
removeSquare[1] = linkY;
possibleSquares.removeElement(removeSquare);
}
}

/**
* a randomization utility.
* @param upper the upper bound for the random int.
* @return a random non-negative int less than the bound upper.
*/
public int getRandomInt(int upper) {
int retVal = myRandom.nextInt() % upper;
if(retVal < 0) { retVal += upper; } return(retVal); } }