### Question:
RLP { public static byte[] encodeBigInteger(BigInteger srcBigInteger) { if (srcBigInteger.equals(BigInteger.ZERO)) { return encodeByte((byte) 0); } else { return encodeElement(asUnsignedByteArray(srcBigInteger)); } }  static int decodeInt(byte[] data, int index); static BigInteger decodeBigInteger(byte[] data, int index); static byte[] decodeIP4Bytes(byte[] data, int index); static int getFirstListElement(byte[] payload, int pos); static int getNextElementIndex(byte[] payload, int pos); static void fullTraverse(byte[] msgData, int level, int startPos,
                                    int endPos, int levelToIndex, Queue<Integer> index); static byte getCommandCode(byte[] data); @Nonnull static ArrayList<RLPElement> decode2(@CheckForNull byte[] msgData); static RLPList decodeList(byte[] msgData); @Nullable static RLPElement decode2OneItem(@CheckForNull byte[] msgData, int startPos); @Nonnull static UscAddress parseUscAddress(@Nullable byte[] bytes); @Nonnull static Coin parseCoin(@Nullable byte[] bytes); @Nullable static Coin parseCoinNonNullZero(byte[] bytes); @Nullable static Coin parseSignedCoinNonNullZero(byte[] bytes); static Coin parseCoinNullZero(@Nullable byte[] bytes); @Nullable static BlockDifficulty parseBlockDifficulty(@Nullable byte[] bytes); static byte[] encode(Object input); static byte[] encodeLength(int length, int offset); static byte[] encodeByte(byte singleByte); static byte[] encodeShort(short singleShort); static byte[] encodeInt(int singleInt); static byte[] encodeString(String srcString); static byte[] encodeBigInteger(BigInteger srcBigInteger); static byte[] encodeUscAddress(UscAddress addr); static byte[] encodeCoin(@Nullable Coin coin); static byte[] encodeCoinNonNullZero(@CheckForNull Coin coin); static byte[] encodeSignedCoinNonNullZero(@CheckForNull Coin coin); static byte[] encodeCoinNullZero(Coin coin); static byte[] encodeBlockDifficulty(BlockDifficulty difficulty); static byte[] encodeElement(@Nullable byte[] srcData); static byte[] encodeListHeader(int size); static byte[] encodeLongElementHeader(int length); static byte[] encodeSet(Set<ByteArrayWrapper> data); static byte[] encodeList(byte[]... elements);  }### Answer:
@Test public void test6() { byte[] expected = new byte[]{(byte) 0x80}; byte[] data = encodeBigInteger(BigInteger.ZERO); assertArrayEquals(expected, data); }
@Test public void testEncodeBigInteger() { BigInteger test = new BigInteger("100102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f", 16); String expected = "a0100102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f"; byte[] encoderesult = encode(test); assertEquals(expected, Hex.toHexString(encoderesult)); byte[] decodeResult = decode2(encoderesult).get(0).getRLPData(); assertEquals(test, BigIntegers.fromUnsignedByteArray(decodeResult)); }
@Test public void encodeBigIntegerEdge_1() { BigInteger integer = new BigInteger("80", 10); byte[] encodedData = encodeBigInteger(integer); System.out.println(Hex.toHexString(encodedData)); }