private String aValue = null;
  private String getAValue() {
    if (aValue == null)
      aValue = compute();
    return aValue;
  }

  private String compute() {
    // long and heavy computing
    System.out.println("Initiating");
    return null;
  }

 String a1 = getAValue();
 String a2 = getAValue();

private String aValue = null;
  private boolean aValueRequireInit = true;
  private String getAValue() {
    if (aValueRequireInit) {
      aValue = compute();
      aValueRequireInit = false;
    }
    return aValue;
  }

private Optional<String> aValue = Optional.empty();
  private String getAValue() {
    if (!aValue.isPresent()) { // при NULL isPresent() = false
      aValue = Optional.ofNullable(compute());
    }
    return aValue.orElse(null);
  }

  private Optional<String> aValue = null;
  private String getAValue() {
    if (aValue == null) {
      aValue = Optional.ofNullable(compute());
    }
    return aValue.orElse(null);
  }

  private static final Optional<String> NULLABLE = Optional.of("NULL");
  private Optional<String> aValue = NULLABLE;
  private String getAValue() {
    if (NULLABLE.equals(aValue)) {
      aValue = Optional.ofNullable(compute());
    }
    return aValue.orElse(null);
  }

  public void build() {
    ...
    aPOJO.setInvoiceNumber(getInvoice().getNumber());
    aPOJO.setInvoiceDate(getInvoice().getDate());
    ..
    aPOJO.setPaymentTerms(getPaymentTermsService(getInvoice()));
    ..
    aPOJO.setInstruction(getInvoiceHeaderInstructions());
   ..
    aPOJO.setTrufficInfo(getTraffic())

  }
  
  // Lazy
  private Invoice getInvoice() {
    // get's invoice from Web Service
  }

  // Lazy
  private BillOfLading getBOL() {
    // get's Bill of lading
  }

// getBOL(), getInvoice() вызываются многократно для получения другой информации.

 private TrufficInfo() {
   return  getBOL().getTruffic();
 }

  private Instruction getInvoiceHeaderInstructions() {
    return getInvoice().getInstructon();
  }