public String getPrivateKeyAsHex() {
        return ByteUtils.formatHex(getPrivKeyBytes());
    }
@Test
    public void testGetPrivateKeyAsHex() {
        ECKey key = ECKey.fromPrivate(BigInteger.TEN).decompress(); // An example private key.
        assertEquals("000000000000000000000000000000000000000000000000000000000000000a", key.getPrivateKeyAsHex());
    }