Add a couple of utility methods for working with P2SH scripts.

core/src/main/java/com/google/bitcoin/core/Address.java

@@ -18,10 +18,12 @@ package com.google.bitcoin.core;
 
 import com.google.bitcoin.params.MainNetParams;
 import com.google.bitcoin.params.TestNet3Params;
+import com.google.bitcoin.script.Script;
 
 import javax.annotation.Nullable;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
 
 /**
  * <p>A Bitcoin address looks like 1MsScoe2fTJoq4ZPdQgqyhgWeoNamYPevy and is derived from an elliptic curve public key
@@ -47,11 +49,27 @@ public class Address extends VersionedChecksummedBytes {
      */
     public Address(NetworkParameters params, int version, byte[] hash160) throws WrongNetworkException {
         super(version, hash160);
+        checkNotNull(params);
         checkArgument(hash160.length == 20, "Addresses are 160-bit hashes, so you must provide 20 bytes");
         if (!isAcceptableVersion(params, version))
             throw new WrongNetworkException(version, params.getAcceptableAddressCodes());
     }
 
+    /** Returns an Address that represents the given P2SH script hash. */
+    public static Address fromP2SHScript(NetworkParameters params, byte[] hash160) {
+        try {
+            return new Address(params, params.getP2SHHeader(), hash160);
+        } catch (WrongNetworkException e) {
+            throw new RuntimeException(e);  // Cannot happen.
+        }
+    }
+
+    /** Returns an Address that represents the script hash extracted from the given scriptPubKey */
+    public static Address fromP2SHScript(NetworkParameters params, Script scriptPubKey) {
+        checkArgument(scriptPubKey.isPayToScriptHash(), "Not a P2SH script");
+        return fromP2SHScript(params, scriptPubKey.getPubKeyHash());
+    }
+
     /**
      * Construct an address from parameters and the hash160 form. Example:<p>
      *

core/src/main/java/com/google/bitcoin/script/ScriptBuilder.java

@@ -136,4 +136,14 @@ public class ScriptBuilder {
             builder.data(signature);
         return builder.build();
     }
+
+    /**
+     * Creates a scriptPubKey that sends to the given script hash. Read
+     * <a href="https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki">BIP 16</a> to learn more about this
+     * kind of script.
+     */
+    public static Script createP2SHOutputScript(byte[] hash) {
+        checkArgument(hash.length == 20);
+        return new ScriptBuilder().op(OP_HASH160).data(hash).op(OP_EQUAL).build();
+    }
 }

core/src/test/java/com/google/bitcoin/core/AddressTest.java

@@ -18,6 +18,7 @@ package com.google.bitcoin.core;
 
 import com.google.bitcoin.params.MainNetParams;
 import com.google.bitcoin.params.TestNet3Params;
+import com.google.bitcoin.script.ScriptBuilder;
 import org.junit.Test;
 import org.spongycastle.util.encoders.Hex;
 
@@ -110,9 +111,12 @@ public class AddressTest {
         assertEquals(TestNet3Params.get().getId(), testNetParams.getId());
 
         // Test that we can convert them from hashes
-        Address a = new Address(mainParams, MainNetParams.get().p2shHeader, Hex.decode("2ac4b0b501117cc8119c5797b519538d4942e90e"));
+        byte[] hex = Hex.decode("2ac4b0b501117cc8119c5797b519538d4942e90e");
+        Address a = Address.fromP2SHScript(mainParams, hex);
         assertEquals("35b9vsyH1KoFT5a5KtrKusaCcPLkiSo1tU", a.toString());
-        Address b = new Address(testParams, TestNet3Params.get().p2shHeader, Hex.decode("18a0e827269b5211eb51a4af1b2fa69333efa722"));
+        Address b = Address.fromP2SHScript(testParams, Hex.decode("18a0e827269b5211eb51a4af1b2fa69333efa722"));
         assertEquals("2MuVSxtfivPKJe93EC1Tb9UhJtGhsoWEHCe", b.toString());
+        Address c = Address.fromP2SHScript(mainParams, ScriptBuilder.createP2SHOutputScript(hex));
+        assertEquals("35b9vsyH1KoFT5a5KtrKusaCcPLkiSo1tU", c.toString());
     }
 }