getHex.java

public class BaseConversion {
  
  private static final char[]    HEXES    = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

  public static String getHex(long value) {
    final StringBuilder hex = new StringBuilder(16);

    byte[] result = new byte[8];
    for (int i = 7; i >= 0; i--) {
      result[i] = (byte) (value & 0xffL);
      value >>= 8;
    }

    for (final byte b : result) {
      char c1 = HEXES[(b & 0xF0) >> 4];
      char c2 = HEXES[(b & 0x0F)];
      hex
        .append(c1)
        .append(c2);
    }

    return hex.toString();
  }
}