Polish FeePolicy

- Convert static fields to final instance fields

 - Remove commented code

 - Rethrow any AddressFormatException as a BitsquareException instead of
   logging and returning null (doing so would cause NPEs in BitcoinJ
   internals).

src/main/java/io/bitsquare/btc/FeePolicy.java

@@ -17,6 +17,8 @@
 
 package io.bitsquare.btc;
 
+import io.bitsquare.BitsquareException;
+
 import org.bitcoinj.core.Address;
 import org.bitcoinj.core.AddressFormatException;
 import org.bitcoinj.core.Coin;
@@ -28,27 +30,21 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 public class FeePolicy {
+
     public static final Coin TX_FEE = Transaction.REFERENCE_DEFAULT_MIN_TX_FEE;
 
-    // The min. REGISTRATION_FEE calculated with Transaction.MIN_NONDUST_OUTPUT would be 0.00015460 which might lead
+    // The min. REGISTRATION_FEE calculated with Transaction.MIN_NONDUST_OUTPUT would be
-    // to problems for the spending wallet.
+    // 0.00015460 which might lead to problems for the spending wallet.
     // Some web wallets don't allow more then 4 decimal places (need more investigation)
     // So we use 0.0002 as that fits also to our 4 decimal places restriction for BTC values.
     // The remaining 0.0000454 BTC is given to miners at the moment as it is lower then dust.
     public static final Coin REGISTRATION_FEE = TX_FEE.add(TX_FEE);
-
     public static final Coin CREATE_OFFER_FEE = REGISTRATION_FEE; // 0.0002
     public static final Coin TAKE_OFFER_FEE = CREATE_OFFER_FEE;
-    private static final Logger log = LoggerFactory.getLogger(FeePolicy.class);
-
-    // those are just dummy yet. trading fees will go probably to arbiters
-    // Not used at the moment
-    // private static final String registrationFeeAddress = "mvkDXt4QmN4Nq9dRUsRigBCaovde9nLkZR";
-
-    private static String createOfferFeeAddress;
-    private static String takeOfferFeeAddress;
 
     private final BitcoinNetwork bitcoinNetwork;
+    private final String createOfferFeeAddress;
+    private final String takeOfferFeeAddress;
 
     @Inject
     public FeePolicy(BitcoinNetwork bitcoinNetwork) {
@@ -68,28 +64,17 @@ public class FeePolicy {
                 createOfferFeeAddress = "n2upbsaKAe4PD3cc4JfS7UCqPC5oNd7Ckg";
                 takeOfferFeeAddress = "n2upbsaKAe4PD3cc4JfS7UCqPC5oNd7Ckg";
                 break;
+            default:
+                throw new BitsquareException("Unknown bitcoin network: %s", bitcoinNetwork);
         }
     }
 
-    //TODO who is receiver? other users or dev address? use donation option list?
-    // Not used at the moment
-    // (dev, other users, wikileaks, tor, sub projects (bitcoinj, tomp2p,...)...)
- /*   public Address getAddressForRegistrationFee() {
-        try {
-            return new Address(params, registrationFeeAddress);
-        } catch (AddressFormatException e) {
-             e.printStackTrace();
-            return null;
-        }
-    }*/
-
     //TODO get address form arbitrator list
     public Address getAddressForCreateOfferFee() {
         try {
             return new Address(bitcoinNetwork.getParameters(), createOfferFeeAddress);
-        } catch (AddressFormatException e) {
+        } catch (AddressFormatException ex) {
-            e.printStackTrace();
+            throw new BitsquareException(ex);
-            return null;
         }
     }
 
@@ -97,9 +82,8 @@ public class FeePolicy {
     public Address getAddressForTakeOfferFee() {
         try {
             return new Address(bitcoinNetwork.getParameters(), takeOfferFeeAddress);
-        } catch (AddressFormatException e) {
+        } catch (AddressFormatException ex) {
-            e.printStackTrace();
+            throw new BitsquareException(ex);
-            return null;
         }
     }
 }