Java是当前互联网行业最流行的编程语言之一，它具有跨平台性、稳定性和高性能等优点，因此在软件开发领域中得到了广泛应用。对于想要从事Java编程的人来说，掌握Java编程技能不仅对于找工作有帮助，也可以提高他们的职业竞争力。那么学习Java能干几年呢？以下是一些实战代码案例分析，帮助Java程序员探索他们的职业发展之路。

1. Java Web开发

Java Web开发是Java程序员最常见的领域之一。在这个领域，你需要掌握Java基础知识、Web技术、数据库等多个方面。一个典型的Java Web开发案例是搭建一个在线商城网站。为了实现这个目标，你需要使用Spring框架、MyBatis技术、MySQL数据库等。以下是一个Java Web开发案例的实现代码：

@Controller
@RequestMapping("/product")
public class ProductController {
  @Autowired
  private ProductService productService;
  @GetMapping("/{id}")
  public ModelAndView getProduct(@PathVariable("id") Long id) {
    Product product = productService.getProductById(id);
    return new ModelAndView("product/productDetail", "product", product);
  }
  @PostMapping("/add")
  public String saveProduct(Product product, BindingResult result, HttpServletRequest request) {
    //校验表单数据
    if (result.hasErrors())
      return "product/editProduct";
    
    //保存商品
    productService.saveProduct(product);
    return "redirect:/product/list";
  }
  @PutMapping("/update/{id}")
  public String updateProduct(@PathVariable("id") Long id, Product product) {
    productService.updateProduct(id, product);
    return "redirect:/product/list";
  }
  @DeleteMapping("/delete/{id}")
  public String deleteProduct(@PathVariable("id") Long id) {
    productService.deleteProduct(id);
    return "redirect:/product/list";
  }
}
@Service
public class ProductServiceImpl implements ProductService {
  @Autowired
  private ProductDao productDao;
  @Override
  public Product getProductById(Long id) {
    return productDao.getProductById(id);
  }
  @Override
  public List
  getProductList() {
 
    return productDao.getProductList();
  }
  @Override
  public void saveProduct(Product product) {
    productDao.saveProduct(product);
  }
  @Override
  public void updateProduct(Long id, Product product) {
    productDao.updateProduct(id, product);
  }
  @Override
  public void deleteProduct(Long id) {
    productDao.deleteProduct(id);
  }
}
@Repository
public class ProductDaoImpl implements ProductDao {
  @Autowired
  private JdbcTemplate jdbcTemplate;
  @Override
  public Product getProductById(Long id) {
    String sql = "SELECT * FROM product WHERE id=?";
    return jdbcTemplate.queryForObject(sql, new Object[]{id}, new BeanPropertyRowMapper<>(Product.class));
  }
  @Override
  public List
  getProductList() {
 
    String sql = "SELECT * FROM product";
    return jdbcTemplate.query(sql, new BeanPropertyRowMapper<>(Product.class));
  }
  @Override
  public void saveProduct(Product product) {
    String sql = "INSERT INTO product(name, price, description) VALUES (?, ?, ?)";
    jdbcTemplate.update(sql, product.getName(), product.getPrice(), product.getDescription());
  }
  @Override
  public void updateProduct(Long id, Product product) {
    String sql = "UPDATE product SET name=?, price=?, description=? WHERE id=?";
    jdbcTemplate.update(sql, product.getName(), product.getPrice(), product.getDescription(), id);
  }
  @Override
  public void deleteProduct(Long id) {
    String sql = "DELETE FROM product WHERE id=?";
    jdbcTemplate.update(sql, id);
  }
}

2. Java桌面应用开发

Java桌面应用开发是另一个广泛应用的领域。Java平台提供了一个名为Swing的GUI工具包，可用于开发跨平台的桌面应用程序。一个典型的Java桌面应用程序案例是开发一个音乐播放器。以下是一个Java桌面应用程序案例的实现代码：

public class MusicPlayer extends JFrame {
  public MusicPlayer() {
    initComponents();
  }
  private void initComponents() {
    //窗口设置
    setTitle("MusicPlayer");
    setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    setLocationByPlatform(true);
    //播放列表
    DefaultListModel
  playlistModel = new DefaultListModel<>();
 
    playlistModel.addElement("song1.mp3");
    playlistModel.addElement("song2.mp3");
    JList
  playlist = new JList<>(playlistModel);
 
    //播放控制面板
    JPanel controlPanel = new JPanel(new FlowLayout());
    JButton playButton = new JButton("Play");
    JButton pauseButton = new JButton("Pause");
    JButton stopButton = new JButton("Stop");
    controlPanel.add(playButton);
    controlPanel.add(pauseButton);
    controlPanel.add(stopButton);
    //添加组件
    add(new JScrollPane(playlist), BorderLayout.CENTER);
    add(controlPanel, BorderLayout.SOUTH);
    //注册事件
    playButton.addActionListener(e -> {
      String fileName = playlist.getSelectedValue();
      //TODO: 播放音乐
    });
    pauseButton.addActionListener(e -> {
      //TODO: 暂停播放
    });
    stopButton.addActionListener(e -> {
      //TODO: 停止播放
    });
  }
  public static void main(String[] args) {
    MusicPlayer player = new MusicPlayer();
    player.pack();
    player.setVisible(true);
  }
}

3. Java游戏开发

Java游戏开发是相对较少的领域，但它仍然有着比较有趣的项目。Java游戏通常被用于开发小型游戏，因为Java语言在性能方面的表现并不像C++那么优秀。一个典型的Java游戏案例是开发一个俄罗斯方块游戏。以下是一个Java游戏案例的实现代码：

public class TetrisGame extends JFrame {
  public TetrisGame() {
    super("Tetris Game");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(220, 440);
    setResizable(false);
    setLocationRelativeTo(null);
    add(new TetrisBoard());
    setVisible(true);
  }
  public static void main(String[] args) {
    new TetrisGame();
  }
}
class TetrisBoard extends JPanel implements ActionListener {
  private final int size = 30;
  private final int boardWidth = 10;
  private final int boardHeight = 22;
  private final Timer timer;
  private boolean isGameOver;
  private Tetromino falling;
  private final ArrayList
  landed;
 
  private static final Color[] COLORS = {
      Color.BLACK, Color.CYAN, Color.blue, Color.orange, Color.yellow, Color.green, Color.pink, Color.red};
  private static final int[][][] SHAPES = {
      {{0, 0}, {0, 0}, {0, 0}, {0, 0}},
      {{0, -1}, {0, 0}, {-1, 0}, {-1, 1}}, //S
      {{0, -1}, {0, 0}, {1, 0}, {1, 1}}, //Z
      {{0, -1}, {0, 0}, {0, 1}, {0, 2}}, //I
      {{-1, 0}, {0, 0}, {1, 0}, {0, 1}}, //T
      {{0, 0}, {1, 0}, {0, 1}, {1, 1}}, //O
      {{-1, -1}, {0, -1}, {0, 0}, {1, 0}}, //J
      {{1, -1}, {0, -1}, {0, 0}, {-1, 0}} //L
  };
  public TetrisBoard() {
    super();
    setBackground(Color.white);
    landed = new ArrayList<>();
    falling = new Tetromino();
    timer = new Timer(400, this);
    timer.start();
    addKeyListener(new MyAdapter());
    setFocusable(true);
  }
  private boolean checkCollision() {
    for (Block b : falling.blocks) {
      if (b.row < 0 || b.row >= boardHeight || b.col < 0 || b.col >= boardWidth) {
        return true;
      }
      for (Tetromino t : landed) {
        if (t.blocks.contains(b)) {
          return true;
        }
      }
    }
    return false;
  }
  private void checkLanded() {
    if (checkCollision()) {
      if (falling.row == 0) {
        isGameOver = true;
        timer.stop();
      } else {
        landed.add(falling);
        falling = new Tetromino();
      }
    }
  }
  private void drawBlock(Graphics g, int row, int col, Color color) {
    g.setColor(color.lightGray);
    g.fillRect(col * size, row * size, size, size);
    g.setColor(color);
    g.fillRect(col * size + 1, row * size + 1, size - 2, size - 2);
  }
  private void drawLand(Graphics g) {
    for (Tetromino t : landed) {
      for (Block b : t.blocks) {
        drawBlock(g, b.row, b.col, COLORS[t.color]);
      }
    }
  }
  private void drawFalling(Graphics g) {
    for (Block b : falling.blocks) {
      drawBlock(g, b.row, b.col, COLORS[falling.color]);
    }
  }
  private void drawGameOver(Graphics g) {
    g.setColor(Color.red);
    g.drawString("Game Over", 60, boardHeight * size / 2);
  }
  @Override
  public void actionPerformed(ActionEvent e) {
    if (!isGameOver) {
      falling.moveDown();
      checkLanded();
    }
    repaint();
  }
  @Override
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    drawLand(g);
    drawFalling(g);
    if (isGameOver) {
      drawGameOver(g);
    }
  }
  private class MyAdapter extends KeyAdapter {
    @Override
    public void keyPressed(KeyEvent e) {
      int keycode = e.getKeyCode();
      switch (keycode) {
        case KeyEvent.VK_LEFT:
          falling.moveLeft();
          break;
        case KeyEvent.VK_RIGHT:
          falling.moveRight();
          break;
        case KeyEvent.VK_UP:
          falling.rotate();
          break;
        case KeyEvent.VK_DOWN:
          falling.moveDown();
          checkLanded();
          break;
      }
      repaint();
    }
  }
  private class Tetromino {
    private final ArrayList
  blocks;
 
    private int row;
    private int col;
    private int color;
    public Tetromino() {
      blocks = new ArrayList<>();
      row = 0;
      col = boardWidth / 2;
      color = (int) (Math.random() * 7) + 1;
      int type = color % 7;
      for (int i = 0; i < 4; i++) {
        blocks.add(new Block(row + SHAPES[type][i][0], col + SHAPES[type][i][1]));
      }
    }
    public void moveLeft() {
      for (Block b : blocks) {
        b.col--;
      }
      if (checkCollision()) {
        moveRight();
      }
    }
    public void moveRight() {
      for (Block b : blocks) {
        b.col++;
      }
      if (checkCollision()) {
        moveLeft();
      }
    }
    public void moveDown() {
      for (Block b : blocks) {
        b.row++;
      }
    }
    public void rotate() {
      if (color == 2) {  //Z
        return;
      }
      int type = color % 7;
      int[][] temp = new int[4][2];
      for (int i = 0; i < 4; i++) {
        temp[i][0] = SHAPES[type][i][1];
        temp[i][1] = -SHAPES[type][i][0];
      }
      for (int i = 0; i < 4; i++) {
        blocks.get(i).row = row + temp[i][1];
        blocks.get(i).col = col + temp[i][0];
      }
      if (checkCollision()) {
        for (Block b : blocks) {
          b.row -= temp[b.index][1];
          b.col -= temp[b.index][0];
        }
      }
    }
  }
  private static class Block {
    int row;
    int col;
    final int index;
    public Block(int r, int c) {
      row = r;
      col = c;
      index = TetrominoManager.getIndex();
    }
    @Override
    public boolean equals(Object obj) {
      if (this == obj) {
        return true;
      }
      if (obj == null || getClass() != obj.getClass()) {
        return false;
      }
      Block block = (Block) obj;
      return index == block.index;
    }
    @Override
    public int hashCode() {
      return Objects.hash(index);
    }
  }
  private static class TetrominoManager {
    private static int index;
    public static int getIndex() {
      index++;
      return index - 1;
    }
  }
}

Web开发，Java桌面应用开发，Java游戏开发。

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