Java 遊戲程式設計：用鍵盤控制控制兩個長方形 ( Java Game Programming: Controlling two Sprites with the Keyboard )

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底下的範例為未完成的乒乓球遊戲，用來說明如何同時控制兩個矩形。
程式執行畫面：

鍵盤操作說明

向上鍵 --> 控制綠色板子往上移

向下鍵 --> 控制綠色板子往下移

W鍵 --> 控制藍色板子往上移

X鍵 --> 控制藍色板子往下移

程式碼：

	package holan.tw;
	import java.awt.Color;
	import java.awt.Graphics;
	import java.awt.event.ActionEvent;
	import java.awt.event.ActionListener;
	import java.awt.event.KeyEvent;
	import java.awt.event.KeyListener;
	import javax.swing.JFrame;
	import javax.swing.Timer;
	public class PingPongGame extends JFrame implements KeyListener, ActionListener {
	// 遊戲畫面大小
	final int SCREEN_WIDTH = 400;
	final int SCREEN_HEIGHT = 400;
	// 球的初始位置
	final int INIT_Y_POS = SCREEN_HEIGHT / 2;
	final int INIT_X_POS = SCREEN_WIDTH / 2;
	// 擊球板子的大小
	final int PAD_WIDTH = 20;
	final int PAD_HEIGHT = 100;
	final int PLAYER_NUM = 2;
	final int PAD_OFFSET = 10;
	// 更新球位置的計時器
	Timer ballTimer;
	// 球移動的速度
	int ballSpeedX = 1, ballSpeedY = 1;
	final int DELAY_MS = 20;
	// 球的位置
	int ballPosX = INIT_X_POS;
	int ballPosY = INIT_Y_POS;
	// 球的大小
	final int BALL_RADIUS = 20;
	// 玩家移動板子的速度
	int playerSpeedY = 20;
	// 玩家板子的位置
	int[] playerPosX = new int[PLAYER_NUM];
	int[] playerPosY = new int[PLAYER_NUM];
	public PingPongGame() {
	setTitle("遊戲基礎-乒乓球");
	setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	setLocationRelativeTo(null);
	addKeyListener(this);
	initPlayerPos();
	initBallTimer();
	}
	private void initBallTimer() {
	ballTimer = new Timer(DELAY_MS, this);
	ballTimer.setInitialDelay(190);
	ballTimer.start();
	}
	private void initPlayerPos() {
	for(int i = 0; i < PLAYER_NUM; i++) {
	playerPosY[i] = INIT_Y_POS;
	}
	playerPosX[0] = PAD_OFFSET;
	playerPosX[1] = SCREEN_WIDTH - PAD_WIDTH - PAD_OFFSET;
	}
	public void update(Graphics g) {
	this.paint(g);
	}
	public void paint(Graphics g) {
	super.paint(g);
	drawPlayerPad(g);
	drawBall(g);
	}
	private void drawPlayerPad(Graphics g) {
	g.setColor(Color.GREEN);
	g.fillRect(playerPosX[0], playerPosY[0], PAD_WIDTH, PAD_HEIGHT);
	g.setColor(Color.BLUE);
	g.fillRect(playerPosX[1], playerPosY[1], PAD_WIDTH, PAD_HEIGHT);
	}
	private void drawBall(Graphics g) {
	g.setColor(Color.CYAN);
	g.fillOval(ballPosX, ballPosY, BALL_RADIUS, BALL_RADIUS);
	}
	public static void main(String[] args) {
	new PingPongGame().show();
	}
	@Override
	public void keyPressed(KeyEvent e) {
	int key = e.getKeyCode();
	// Move the player on the left
	if( key == KeyEvent.VK_UP )
	playerPosY[0] -= playerSpeedY;
	if( key == KeyEvent.VK_DOWN )
	playerPosY[0] += playerSpeedY;
	// Move the player on the right
	if( key == KeyEvent.VK_W )
	playerPosY[1] -= playerSpeedY;
	if( key == KeyEvent.VK_X )
	playerPosY[1] += playerSpeedY;
	checkPadPosRange();
	repaint();
	}
	// 檢查板子是否超出遊戲畫面的範圍
	private void checkPadPosRange() {
	for(int i = 0; i < PLAYER_NUM; i++) {
	if( playerPosY[i] < 0) playerPosY[i] = 0;
	if( playerPosY[i] > SCREEN_HEIGHT - PAD_HEIGHT) playerPosY[i] = SCREEN_HEIGHT - PAD_HEIGHT;
	}
	}
	@Override
	public void keyReleased(KeyEvent e) {
	}
	@Override
	public void keyTyped(KeyEvent e) {
	}
	@Override
	public void actionPerformed(ActionEvent e) {
	ballPosX += ballSpeedX;
	ballPosY += ballSpeedY;
	// 球是否碰到遊戲畫面邊界
	if( ballPosX >= SCREEN_WIDTH - BALL_RADIUS || ballPosX <= 0 ) ballSpeedX = -ballSpeedX;
	if( ballPosY >= SCREEN_HEIGHT - BALL_RADIUS || ballPosY <= BALL_RADIUS) ballSpeedY = -ballSpeedY;
	this.repaint();
	}
	}

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