code: @Deprecated
      public static String getFC_NFKC_Closure(int c) {
          // Compute the FC_NFKC_Closure on the fly:
          // We have the API for complete coverage of Unicode properties, although
          // this value by itself is not useful via API.
          // (What could be useful is a custom normalization table that combines
          // case folding and NFKC.)
          // For the derivation, see Unicode's DerivedNormalizationProps.txt.
          Normalizer2 nfkc=NFKCModeImpl.INSTANCE.normalizer2;
          UCaseProps csp=UCaseProps.INSTANCE;
          // first: b = NFKC(Fold(a))
          StringBuilder folded=new StringBuilder();
          int folded1Length=csp.toFullFolding(c, folded, 0);
          if(folded1Length<0) {
              Normalizer2Impl nfkcImpl=((Norm2AllModes.Normalizer2WithImpl)nfkc).impl;
              if(nfkcImpl.getCompQuickCheck(nfkcImpl.getNorm16(c))!=0) {
                  return "";  // c does not change at all under CaseFolding+NFKC
              }
              folded.appendCodePoint(c);
          } else {
              if(folded1Length>UCaseProps.MAX_STRING_LENGTH) {
                  folded.appendCodePoint(folded1Length);
              }
          }
          String kc1=nfkc.normalize(folded);
          // second: c = NFKC(Fold(b))
          String kc2=nfkc.normalize(UCharacter.foldCase(kc1, 0));
          // if (c != b) add the mapping from a to c
          if(kc1.equals(kc2)) {
              return "";
          } else {
              return kc2;
          }
      }
docs: Gets the FC_NFKC closure value.
  @param c The code point whose closure value is to be retrieved
  @return String representation of the closure value; "" if there is none
  @deprecated ICU 56
  @hide original deprecated declaration