Block: add new constructors to reduce mutability

* New constructors and static factory methods
* Update code to use the new constructors
* Remove `public` from `@VisibleForTesting` setters where possible

core/src/main/java/org/bitcoinj/core/Block.java

@@ -51,6 +51,7 @@ import java.util.Date;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Objects;
 
 import static org.bitcoinj.base.Coin.FIFTY_COINS;
 import static org.bitcoinj.base.Sha256Hash.hashTwice;
@@ -178,13 +179,32 @@ public class Block extends BaseMessage {
         return transactions;
     }
 
-    /** Special case constructor, used for the genesis node, cloneAsHeader and unit tests. */
+    /** Special case constructor, used for unit tests. */
+    @VisibleForTesting
     Block(long setVersion) {
         // Set up a few basic things. We are not complete after this though.
-        version = setVersion;
+        this(setVersion,
-        difficultyTarget = 0x1d07fff8L;
+                TimeUtils.currentTime().truncatedTo(ChronoUnit.SECONDS), // convert to Bitcoin time)
-        time = TimeUtils.currentTime().truncatedTo(ChronoUnit.SECONDS); // convert to Bitcoin time
+                0x1d07fff8L,
-        prevBlockHash = Sha256Hash.ZERO_HASH;
+                0,
+                Collections.emptyList());
+    }
+
+    // For unit-test genesis blocks
+    @VisibleForTesting
+    Block(long setVersion, Instant time, long difficultyTarget, List<Transaction> transactions) {
+        this(setVersion, time, difficultyTarget, 0, transactions);
+        // Solve for nonce?
+    }
+
+    // For genesis blocks (and also unit tests)
+    Block(long setVersion, Instant time, long difficultyTarget, long nonce, List<Transaction> transactions) {
+        this.version = setVersion;
+        this.time = time;
+        this.difficultyTarget = difficultyTarget;
+        this.nonce = nonce;
+        this.prevBlockHash = Sha256Hash.ZERO_HASH;
+        this.transactions = new ArrayList<>(Objects.requireNonNull(transactions));
     }
 
     /**
@@ -229,12 +249,18 @@ public class Block extends BaseMessage {
                 transactions);
     }
 
-    public static Block createGenesis() {
+    public static Block createGenesis(Instant time, long difficultyTarget) {
-        Block genesisBlock = new Block(BLOCK_VERSION_GENESIS);
+        return new Block(BLOCK_VERSION_GENESIS, time, difficultyTarget, genesisTransactions());
+    }
+
+    public static Block createGenesis(Instant time, long difficultyTarget, long nonce) {
+        return new Block(BLOCK_VERSION_GENESIS, time, difficultyTarget, nonce, genesisTransactions());
+    }
+
+    private static List<Transaction> genesisTransactions() {
         Transaction tx = Transaction.coinbase(genesisTxInputScriptBytes);
         tx.addOutput(new TransactionOutput(tx, FIFTY_COINS, genesisTxScriptPubKeyBytes));
-        genesisBlock.addTransaction(tx);
+        return Collections.singletonList(tx);
-        return genesisBlock;
     }
 
     // A script containing the difficulty bits and the following message:
@@ -367,14 +393,8 @@ public class Block extends BaseMessage {
      * @return new, header-only {@code Block}
      */
     public Block cloneAsHeader() {
-        Block block = new Block(version);
+        Block block = new Block(version, prevBlockHash, getMerkleRoot(), time, difficultyTarget, nonce, null);
-        block.difficultyTarget = difficultyTarget;
-        block.time = time;
-        block.nonce = nonce;
-        block.prevBlockHash = prevBlockHash;
-        block.merkleRoot = getMerkleRoot();
         block.hash = getHash();
-        block.transactions = null;
         return block;
     }
 
@@ -729,7 +749,7 @@ public class Block extends BaseMessage {
     }
 
     @VisibleForTesting
-    public void setTime(Instant time) {
+    void setTime(Instant time) {
         unCacheHeader();
         this.time = time.truncatedTo(ChronoUnit.SECONDS); // convert to Bitcoin time
         this.hash = null;
@@ -750,7 +770,7 @@ public class Block extends BaseMessage {
 
     /** Sets the difficulty target in compact form. */
     @VisibleForTesting
-    public void setDifficultyTarget(long compactForm) {
+    void setDifficultyTarget(long compactForm) {
         unCacheHeader();
         this.difficultyTarget = compactForm;
         this.hash = null;
@@ -766,7 +786,7 @@ public class Block extends BaseMessage {
 
     /** Sets the nonce and clears any cached data. */
     @VisibleForTesting
-    public void setNonce(long nonce) {
+    void setNonce(long nonce) {
         unCacheHeader();
         this.nonce = nonce;
         this.hash = null;

core/src/main/java/org/bitcoinj/params/MainNetParams.java

@@ -134,10 +134,7 @@ public class MainNetParams extends BitcoinNetworkParams {
     public Block getGenesisBlock() {
         synchronized (GENESIS_HASH) {
             if (genesisBlock == null) {
-                genesisBlock = Block.createGenesis();
+                genesisBlock = Block.createGenesis(GENESIS_TIME, Block.STANDARD_MAX_DIFFICULTY_TARGET, GENESIS_NONCE);
-                genesisBlock.setDifficultyTarget(Block.STANDARD_MAX_DIFFICULTY_TARGET);
-                genesisBlock.setTime(GENESIS_TIME);
-                genesisBlock.setNonce(GENESIS_NONCE);
                 checkState(genesisBlock.getHash().equals(GENESIS_HASH), () -> "invalid genesis hash");
             }
         }

core/src/main/java/org/bitcoinj/params/RegTestParams.java

@@ -82,10 +82,7 @@ public class RegTestParams extends BitcoinNetworkParams {
     public Block getGenesisBlock() {
         synchronized (GENESIS_HASH) {
             if (genesisBlock == null) {
-                genesisBlock = Block.createGenesis();
+                genesisBlock = Block.createGenesis(GENESIS_TIME, Block.EASIEST_DIFFICULTY_TARGET, GENESIS_NONCE);
-                genesisBlock.setDifficultyTarget(Block.EASIEST_DIFFICULTY_TARGET);
-                genesisBlock.setTime(GENESIS_TIME);
-                genesisBlock.setNonce(GENESIS_NONCE);
                 checkState(genesisBlock.getHash().equals(GENESIS_HASH), () ->
                         "invalid genesis hash");
             }

core/src/main/java/org/bitcoinj/params/SigNetParams.java

@@ -79,10 +79,7 @@ public class SigNetParams extends BitcoinNetworkParams {
     public Block getGenesisBlock() {
         synchronized (GENESIS_HASH) {
             if (genesisBlock == null) {
-                genesisBlock = Block.createGenesis();
+                genesisBlock = Block.createGenesis(GENESIS_TIME, GENESIS_DIFFICULTY, GENESIS_NONCE);
-                genesisBlock.setDifficultyTarget(GENESIS_DIFFICULTY);
-                genesisBlock.setTime(GENESIS_TIME);
-                genesisBlock.setNonce(GENESIS_NONCE);
                 checkState(genesisBlock.getHash().equals(GENESIS_HASH), () ->
                         "invalid genesis hash");
             }

core/src/main/java/org/bitcoinj/params/TestNet3Params.java

@@ -88,10 +88,7 @@ public class TestNet3Params extends BitcoinNetworkParams {
     public Block getGenesisBlock() {
         synchronized (GENESIS_HASH) {
             if (genesisBlock == null) {
-                genesisBlock = Block.createGenesis();
+                genesisBlock = Block.createGenesis(GENESIS_TIME, Block.STANDARD_MAX_DIFFICULTY_TARGET, GENESIS_NONCE);
-                genesisBlock.setDifficultyTarget(Block.STANDARD_MAX_DIFFICULTY_TARGET);
-                genesisBlock.setTime(GENESIS_TIME);
-                genesisBlock.setNonce(GENESIS_NONCE);
                 checkState(genesisBlock.getHash().equals(GENESIS_HASH), () ->
                         "invalid genesis hash");
             }

core/src/main/java/org/bitcoinj/params/UnitTestParams.java

@@ -73,9 +73,7 @@ public class UnitTestParams extends BitcoinNetworkParams {
     public Block getGenesisBlock() {
         synchronized (this) {
             if (genesisBlock == null) {
-                genesisBlock = Block.createGenesis();
+                genesisBlock = Block.createGenesis(TimeUtils.currentTime(), Block.EASIEST_DIFFICULTY_TARGET);
-                genesisBlock.setDifficultyTarget(Block.EASIEST_DIFFICULTY_TARGET);
-                genesisBlock.setTime(TimeUtils.currentTime());
             }
         }
         return genesisBlock;

core/src/test/java/org/bitcoinj/core/BlockChainTest.java

@@ -414,24 +414,26 @@ public class BlockChainTest {
 
     // Some blocks from the test net.
     private static Block getBlock2() throws Exception {
-        Block b2 = new Block(Block.BLOCK_VERSION_GENESIS);
+        Block b2 = new Block(Block.BLOCK_VERSION_GENESIS,
-        b2.setMerkleRoot(Sha256Hash.wrap("20222eb90f5895556926c112bb5aa0df4ab5abc3107e21a6950aec3b2e3541e2"));
+                Sha256Hash.wrap("00000000b873e79784647a6c82962c70d228557d24a747ea4d1b8bbe878e1206"), // prev
-        b2.setNonce(875942400L);
+                Sha256Hash.wrap("20222eb90f5895556926c112bb5aa0df4ab5abc3107e21a6950aec3b2e3541e2"), // merkle
-        b2.setTime(Instant.ofEpochSecond(1296688946L));
+                Instant.ofEpochSecond(1296688946L),
-        b2.setDifficultyTarget(0x1d00ffff);
+                0x1d00ffff,
-        b2.setPrevBlockHash(Sha256Hash.wrap("00000000b873e79784647a6c82962c70d228557d24a747ea4d1b8bbe878e1206"));
+                875942400L,
+                null);
         assertEquals("000000006c02c8ea6e4ff69651f7fcde348fb9d557a06e6957b65552002a7820", b2.getHashAsString());
         Block.verifyHeader(b2);
         return b2;
     }
 
     private static Block getBlock1() throws Exception {
-        Block b1 = new Block(Block.BLOCK_VERSION_GENESIS);
+        Block b1 = new Block(Block.BLOCK_VERSION_GENESIS,
-        b1.setMerkleRoot(Sha256Hash.wrap("f0315ffc38709d70ad5647e22048358dd3745f3ce3874223c80a7c92fab0c8ba"));
+                Sha256Hash.wrap("000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943"), // prev
-        b1.setNonce(1924588547);
+                Sha256Hash.wrap("f0315ffc38709d70ad5647e22048358dd3745f3ce3874223c80a7c92fab0c8ba"), // merkle
-        b1.setTime(Instant.ofEpochSecond(1296688928));
+                Instant.ofEpochSecond(1296688928),
-        b1.setDifficultyTarget(0x1d00ffff);
+                0x1d00ffff,
-        b1.setPrevBlockHash(Sha256Hash.wrap("000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943"));
+                1924588547,
+                null);
         assertEquals("00000000b873e79784647a6c82962c70d228557d24a747ea4d1b8bbe878e1206", b1.getHashAsString());
         Block.verifyHeader(b1);
         return b1;

core/src/test/java/org/bitcoinj/core/BlockTest.java

@@ -336,10 +336,9 @@ public class BlockTest {
 
     @Test
     public void testGenesisBlock() {
-        Block genesisBlock = Block.createGenesis();
+        Block genesisBlock = Block.createGenesis(Instant.ofEpochSecond(1231006505L),
-        genesisBlock.setDifficultyTarget(0x1d00ffffL);
+                0x1d00ffffL,
-        genesisBlock.setTime(Instant.ofEpochSecond(1231006505L));
+                2083236893);
-        genesisBlock.setNonce(2083236893);
         assertEquals(Sha256Hash.wrap("000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"), genesisBlock.getHash());
     }
 }