code: public float[] getFeature(char... chars) {
          if (chars == null) {
              return null;
          }
          SmartForest<float[]> sf = featureTree;
          sf = sf.getBranch(chars);
          if (sf == null || sf.getParam() == null) {
              return null;
          }
          return sf.getParam();
      }
docs: 获得特征所在权重数组
  
  @param featureStr
  @return