Java中使用HashMap改进查找性能的步骤

// 创建 HashMap 对象 Sites
HashMap<Integer, String> Sites = new HashMap<Integer, String>();
// 添加键值对
Sites.put(1, "Google");
Sites.put(2, "Runoob");
Sites.put(3, "Taobao");
Sites.put(4, "Zhihu");
//读取
String val = Sites.get(1);//得到Google

private HashMap<Long,SimpleItem> recGeo(HashMap<Long, SimpleItem> map,String geo,int j){
  /*
    将相同坐标的记录合成一条
    HashMap<Long, SimpleItem> map, 新集合
    String geo, 坐标字符串
    int j 记录ID
   */

  try {
    Point p = (Point)reader.read(geo);
    /*
      计算哈希值
      因为如果采用循环来比较，数据量太大，速度太慢了
      为避免不同坐标出现经度+纬度结果相同的情况，将经度 * 1000再相加
     */
    //计算Key
    long k = Long.valueOf(Double.doubleToLongBits(p.getX() * 1000 + p.getY())).hashCode();
    
    SimpleItem si = map.get(k);
    if(si != null){//新集合中该Key对应元素已存在，应该是相同坐标的记录
      si.getPointers().add(j);//归并
    } else {//否则插入
      si = new SimpleItem();
      si.setGeo(geo);
      List<Integer> pointers = new ArrayList();
      pointers.add(j);
      si.setPointers(pointers);
      map.put(k,si);
    }
  } catch (ParseException e) {
    e.printStackTrace();
  }

  return map;
}

private static GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory( null );
private static WKTReader reader = new WKTReader( geometryFactory );
class SimpleItem{
  private Point geo;
  private List<Integer> pointers;

  public Point getGeo() {
    return geo;
  }

  public void setGeo(String geo) {
    try {
      this.geo = (Point)reader.read(geo);
    } catch (ParseException e) {
      e.printStackTrace();
    }
  }

  public List<Integer> getPointers() {
    return pointers;
  }

  public void setPointers(List<Integer> pointers) {
    this.pointers = pointers;
  }
}