j2me竖向滚动菜单的基本做法

public class AppCanvas extends Canvas {

  int screen_width;
  int screen_height;
  String[] select;
  public final static int KEY_UP = -1;
  public final static int KEY_DOWN = -2;

  public AppCanvas() {
    this.setFullScreenMode(true);
    screen_width = this.getWidth();
    screen_height = this.getHeight();
    select = new String[] { "登    录", "注    册", "账户充值", "用户提款", "进出明细",
        "投注查询", "中奖查询", "个人资料", "密码修改" };
  }

  private int itemsOnSceen = 5;//最多显示几条，需要根据屏幕大小判断
  private int index = 0;//select的索引
  private int delta = 0;//index超过itemsOnSceen后的偏移量

  protected void paint(Graphics g) {
    // TODO Auto-generated method stub

    g.setColor(0xffffff);
    g.fillRect(0, 0, screen_width, screen_height);
    
    for (int i = 0; i < ((itemsOnSceen>select.length)?select.length:itemsOnSceen); i++) {
      if (i == index - delta) {
        g.setColor(0xff0000);
      } else {
        g.setColor(0);
      }
      g.drawString(select[i + delta], screen_width >> 1, 40 + 20 * i,
          Graphics.BASELINE | Graphics.HCENTER);
    }
    
  }

  protected void keyPressed(int keyCode) {
    // TODO Auto-generated method stub
    switch (keyCode) {

    case KEY_UP:
      if (index > 0) {
        index--;
      }
      if (index - delta < 0) { //小屏
        delta--;
      }
      break;
    case KEY_DOWN:
      if (index < select.length - 1) {
        index++;
      }
      if (index - delta > itemsOnSceen - 1) { //小屏
        delta++;
      }
      break;
    }
    repaint();

  }
}