Javaでスクラッチのようなゲームをつくる

ここでは、Javaで作成したDoodle Jumpゲームのシンプルなコード例を示します。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DoodleJump extends JPanel implements ActionListener {
    private static final int WIDTH = 400;
    private static final int HEIGHT = 600;
    private static final int GROUND = 550;
    private static final int PLAYER_SIZE = 25;
    private static final int PLATFORM_WIDTH = 50;
    private static final int PLATFORM_HEIGHT = 10;
    private static final int PLATFORM_GAP = 200;
    private static final int PLATFORM_COUNT = 6;
    private static final int GRAVITY = 2;
    private static final int JUMP_HEIGHT = 30;

    private Timer timer;
    private int playerX;
    private int playerY;
    private int velocityY;
    private boolean isJumping;
    private Platform[] platforms;

    public DoodleJump() {
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setBackground(Color.BLACK);
        setFocusable(true);
        addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                if (e.getKeyCode() == KeyEvent.VK_SPACE) {
                    if (!isJumping) {
                        isJumping = true;
                        velocityY = -JUMP_HEIGHT;
                    }
                }
            }
        });

        playerX = WIDTH / 2;
        playerY = GROUND;
        velocityY = 0;
        isJumping = false;

        platforms = new Platform[PLATFORM_COUNT];
        for (int i = 0; i < PLATFORM_COUNT; i++) {
            platforms[i] = new Platform((int) (Math.random() * (WIDTH - PLATFORM_WIDTH)), GROUND - i * PLATFORM_GAP);
        }

        timer = new Timer(10, this);
        timer.start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        g.setColor(Color.WHITE);
        g.fillOval(playerX - PLAYER_SIZE / 2, playerY - PLAYER_SIZE / 2, PLAYER_SIZE, PLAYER_SIZE);

        for (Platform platform : platforms) {
            g.fillRect(platform.getX(), platform.getY(), PLATFORM_WIDTH, PLATFORM_HEIGHT);
        }
    }

    public void actionPerformed(ActionEvent e) {
        playerY += velocityY;

        if (isJumping) {
            velocityY += GRAVITY;
        }

        if (playerY > GROUND) {
            playerY = GROUND;
            velocityY = 0;
            isJumping = false;
        }

        for (Platform platform : platforms) {
            if (playerY + PLAYER_SIZE / 2 > platform.getY() && playerY + PLAYER_SIZE / 2 < platform.getY() + PLATFORM_HEIGHT
                    && playerX + PLAYER_SIZE / 2 > platform.getX() && playerX - PLAYER_SIZE / 2 < platform.getX() + PLATFORM_WIDTH) {
                playerY = platform.getY() - PLAYER_SIZE / 2;
                velocityY = 0;
                isJumping = false;
            }
        }

        for (Platform platform : platforms) {
            platform.setY(platform.getY() + GRAVITY);
            if (platform.getY() > HEIGHT) {
                platform.setY(platform.getY() - PLATFORM_GAP * PLATFORM_COUNT);
                platform.setX((int) (Math.random() * (WIDTH - PLATFORM_WIDTH)));
            }
        }

        repaint();
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Doodle Jump");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new DoodleJump());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private class Platform {
        private int x;
        private int y;

        public Platform(int x, int y) {
            this.x = x;
            this.y = y;
        }

        public int getX() {
            return x;
        }

        public int getY() {
            return y;
        }

        public void setX(int x) {
            this.x = x;
        }

        public void setY(int y) {
            this.y = y;
        }
    }
}

空中を舞う小さな落書きのキャラクターを操作し、生成され続けるプラットフォームを飛び上がっていく、シンプルな落書きアクションゲーム。プレイヤーがスペースキーを押すと落書きがジャンプし、プレイヤーはプラットフォームにうまくジャンプして着地し続ける必要がある。着地失敗するとゲームオーバー。プラットフォームは上空で次々と生成されるため、プレイヤーはジャンプを続け、着地できなくなった時点でゲームが終了する。