private static String serializeConstraintClass(Class<? extends Constraint> clazz) {
    String constraintClazz = clazz.getName();
    return CONSTRAINT_HTD_KEY_PREFIX + constraintClazz;
  }
Just write the class to a String representation of the class as a key for the
{@link TableDescriptor}
@param clazz Constraint class to convert to a {@link TableDescriptor} key
@return key to store in the {@link TableDescriptor}
hbase-server/src/main/java/org/apache/hadoop/hbase/constraint/Constraints.java