code: @Override
      public void init(boolean forward) throws CertPathValidatorException {
          if (forward) {
              throw new CertPathValidatorException
                                          ("forward checking not supported");
          }
  
          certIndex = 1;
          explicitPolicy = (expPolicyRequired ? 0 : certPathLen + 1);
          policyMapping = (polMappingInhibited ? 0 : certPathLen + 1);
          inhibitAnyPolicy = (anyPolicyInhibited ? 0 : certPathLen + 1);
      }
docs: Initializes the internal state of the checker from parameters
  specified in the constructor
  
  @param forward a boolean indicating whether this checker should be
  initialized capable of building in the forward direction
  @throws CertPathValidatorException if user wants to enable forward
  checking and forward checking is not supported.