import org.apache.lucene.search.similarities.NormalizationZ; //导入依赖的package包/类
static Normalization parseNormalization(String expr, String c, String mu, String z) {
  if (mu != null && !"H3".equals(expr)) {
    throw new RuntimeException(
        "parameter mu only makes sense for normalization H3");
  }
  if (z != null && !"Z".equals(expr)) {
    throw new RuntimeException(
        "parameter z only makes sense for normalization Z");
  }
  if (c != null && !("H1".equals(expr) || "H2".equals(expr))) {
    throw new RuntimeException(
        "parameter c only makese sense for normalizations H1 and H2");
  }
  if ("H1".equals(expr)) {
    return (c != null) ? new NormalizationH1(Float.parseFloat(c))
                       : new NormalizationH1();
  } else if ("H2".equals(expr)) {
    return (c != null) ? new NormalizationH2(Float.parseFloat(c))
                       : new NormalizationH2();
  } else if ("H3".equals(expr)) {
    return (mu != null) ? new NormalizationH3(Float.parseFloat(mu))
                        : new NormalizationH3();
  } else if ("Z".equals(expr)) {
    return (z != null) ? new NormalizationZ(Float.parseFloat(z))
                       : new NormalizationZ();
  } else if ("none".equals(expr)) {
    return new Normalization.NoNormalization();
  } else {
    throw new RuntimeException("Invalid normalization: " + expr);
  }
}