title: Calculate CRC8-Maxim checksum in Java
body: <p>I'm trying to code a CRC8-Maxim calculator in java but I'm stuck. I've tried many API's such as Jacksum, but nothing worked like it should.
  The only thing I found is this website: <a href="http://www.sunshine2k.de/coding/javascript/crc/crc_js.html" rel="nofollow">http://www.sunshine2k.de/coding/javascript/crc/crc_js.html</a></p>
  
  <p>If I choose the CRC8-Maxim setting, the result is exactly what I need it to be.
  (example: The checksum of VR1,?, should be D7)</p>
  
  <p>Do you have any idea, how I could code that in java?
  I need it for my final school project and there's not much time left.</p>
  
  <p>Thanks in advance!
  Benedikt</p>
  
  <p>[EDIT]
  I tried it with this Code. It has the same lookup table and the same polynomial as the calculator at the website.</p>
  
  <pre><code>import java.io.UnsupportedEncodingException;
  
  public final class Crc8 {
  
  private static final short CRC8_POLYNOMIAL = 0x31;
  private static final short CRC8_INIT_VALUE = 0x0;
  private static final short[] CRC8_LOOKUP_TABLE = {
      0x00, 0x31, 0x62, 0x53, 0xC4, 0xF5, 0xA6, 0x97, 0xB9, 0x88, 0xDB, 0xEA, 0x7D, 0x4C, 0x1F, 0x2E,
      0x43, 0x72, 0x21, 0x10, 0x87, 0xB6, 0xE5, 0xD4, 0xFA, 0xCB, 0x98, 0xA9, 0x3E, 0x0F, 0x5C, 0x6D,
      0x86, 0xB7, 0xE4, 0xD5, 0x42, 0x73, 0x20, 0x11, 0x3F, 0x0E, 0x5D, 0x6C, 0xFB, 0xCA, 0x99, 0xA8,
      0xC5, 0xF4, 0xA7, 0x96, 0x01, 0x30, 0x63, 0x52, 0x7C, 0x4D, 0x1E, 0x2F, 0xB8, 0x89, 0xDA, 0xEB,
      0x3D, 0x0C, 0x5F, 0x6E, 0xF9, 0xC8, 0x9B, 0xAA, 0x84, 0xB5, 0xE6, 0xD7, 0x40, 0x71, 0x22, 0x13,
      0x7E, 0x4F, 0x1C, 0x2D, 0xBA, 0x8B, 0xD8, 0xE9, 0xC7, 0xF6, 0xA5, 0x94, 0x03, 0x32, 0x61, 0x50,
      0xBB, 0x8A, 0xD9, 0xE8, 0x7F, 0x4E, 0x1D, 0x2C, 0x02, 0x33, 0x60, 0x51, 0xC6, 0xF7, 0xA4, 0x95,
      0xF8, 0xC9, 0x9A, 0xAB, 0x3C, 0x0D, 0x5E, 0x6F, 0x41, 0x70, 0x23, 0x12, 0x85, 0xB4, 0xE7, 0xD6,
      0x7A, 0x4B, 0x18, 0x29, 0xBE, 0x8F, 0xDC, 0xED, 0xC3, 0xF2, 0xA1, 0x90, 0x07, 0x36, 0x65, 0x54,
      0x39, 0x08, 0x5B, 0x6A, 0xFD, 0xCC, 0x9F, 0xAE, 0x80, 0xB1, 0xE2, 0xD3, 0x44, 0x75, 0x26, 0x17,
      0xFC, 0xCD, 0x9E, 0xAF, 0x38, 0x09, 0x5A, 0x6B, 0x45, 0x74, 0x27, 0x16, 0x81, 0xB0, 0xE3, 0xD2,
      0xBF, 0x8E, 0xDD, 0xEC, 0x7B, 0x4A, 0x19, 0x28, 0x06, 0x37, 0x64, 0x55, 0xC2, 0xF3, 0xA0, 0x91,
      0x47, 0x76, 0x25, 0x14, 0x83, 0xB2, 0xE1, 0xD0, 0xFE, 0xCF, 0x9C, 0xAD, 0x3A, 0x0B, 0x58, 0x69,
      0x04, 0x35, 0x66, 0x57, 0xC0, 0xF1, 0xA2, 0x93, 0xBD, 0x8C, 0xDF, 0xEE, 0x79, 0x48, 0x1B, 0x2A,
      0xC1, 0xF0, 0xA3, 0x92, 0x05, 0x34, 0x67, 0x56, 0x78, 0x49, 0x1A, 0x2B, 0xBC, 0x8D, 0xDE, 0xEF,
      0x82, 0xB3, 0xE0, 0xD1, 0x46, 0x77, 0x24, 0x15, 0x3B, 0x0A, 0x59, 0x68, 0xFF, 0xCE, 0x9D, 0xAC
  };
  
  private final boolean useLookupTable;
  private short crc8;
  
  public Crc8() {
      this(true);
  }
  
  public Crc8(boolean use_lookup_table) {
      useLookupTable = use_lookup_table;
      reset();
  }
  
  public Crc8 reset() {
      crc8 = CRC8_INIT_VALUE;
      return (this);
  }
  
  public Crc8 update(byte b) {
      if (useLookupTable) {
          crc8 = CRC8_LOOKUP_TABLE[(crc8 ^ b) &amp; 0xFF];
      } else {
          crc8 ^= b;
          crc8 &amp;= 0xFF;
          for (int j = 0; j &lt; 8; j++) {
              if ((crc8 &amp; 1) == 1) {
                  crc8 &gt;&gt;= 1;
                  crc8 ^= CRC8_POLYNOMIAL;
              } else {
                  crc8 &gt;&gt;= 1;
              }
          }
      }
      return (this);
  }
  
  public Crc8 update(byte[] data, int offset, int length) {
      for (int i = offset; i &lt; length; i++) {
          update(data[i]);
      }
      return (this);
  }
  
  public Crc8 update(byte[] data) {
      return update(data, 0, data.length);
  }
  
  public Crc8 update(String s) {
      try {
          return update(s.getBytes("UTF-8"));
      } catch (UnsupportedEncodingException ex) {
          throw new RuntimeException(ex);
      }
  }
  
  public short get() {
      return ((short) (crc8 ^ 0xFF));
  }
  
  /**
   * Return calculated CRC8 in 2 capital hex digits with leading zeros.
   */
  public String getHex() {
      return (String.format("%02X", get()));
  }}
  </code></pre>
  
  <p>And this was the Main-class</p>
  
  <pre><code>public static void main(String[] args) {
      Crc8 crc = new Crc8(true);
      String input = "VR1,?,";
      crc.update(input);
      System.out.println("Input: " + input);
      String result  = crc.getHex();
      System.out.println("Output: " + result);
  
  }
  </code></pre>
  
  <p>But unfournatly the result was E4 and not D7 </p>