C++ to Java Bitwise equivalent

Question

I am trying to convert a C/C++ class into a Java equivalent. It's going ok so far but I've got to this bit of code and Java is complaining.

// Isolate each byte in turn
cRecByte = lpszRec[ lRecByteCount++ ] & 0x00FF;

cRecByte is a char

lpszRec is a LPCSTR

lRecByteCount is a long

This works in the C++ code but won't work in Java.

In my Java code I have exactly the same line with the following differences

cRecByte is a char

lpszRec is a String

lRecByteCount is a long

The errors I get (as I'd expect) are

 Type mismatch: cannot convert from int to char
 Type mismatch: cannot convert from long to int

For some context I'm trying to re-write/emulate a Hash Totaling function that was written in the 1980's that is still used by our legacy systems today. Replacing them with something new would cost a fortune in dev/test costs so I have to continue along this path.

The piece of code I've put up is designed to separate out each character from a given record (line of text).

Any help would greatly appreciated.

Some code as requested - This is from the C++ file. I've only gone as far as where I've got to as the actual class is quite large.

void CHashTotalFile::CalcRecHashTotal( /*[in]*/     LPCSTR lpszRec,
                                       /*[in]*/     DWORD dwRecLen, 
                                       /*[in]*/     long lIteration, 
                                       /*[in,out]*/ UINT64& u64HashTotal,
                                                    SYSTYPE stType ) throw()
{
    char    cRecByte;
    LPCSTR  szNullReplacer = "CALCULATE HASH TOTAL";

    const static int  nLenNullReplacer = lstrlenA( szNullReplacer );
    const static char szRandomMap[] = { 17,
                                        5,
                                        37,
                                        31,
                                        53,
                                        19,
                                        41,
                                        7,
                                        11,
                                        2,
                                        23,
                                        3,
                                        29,
                                        47,
                                        43,
                                        13 };

    // 64bit unsigned integer data types:
    UINT64  u64ByteValue;
    UINT64  u64Carry;

    // long data types:
    long    lByteWord;      // Used in u64ByteValue & offset to random map
    long    lRecByteCount;  // Byte count within (actual) record  - used as subscript to data
    long    lRecByteIndex;  // Byte count within (logical) record - used in hashing calculations

    // int data types:
    int     nAttempts;
    int     nByteDistance;  // 'random' distance which rotates (right) the hash total
    int     nHashDistance;  // 'random distance which rotates (left) the hash total
    int     nWordValue;     // From data - offset to random map for hash distance
    bool    bGenerated = false;

    // No exception calls or error logging here as efficiency is the name of the game!
    // (or not so much inefficiency!)

    // If text & this is a blank line (i.e. \n) set to record length to zero
    if( m_fText && lpszRec[0] == NEWLINE_CHARACTER  )
        dwRecLen = 0;

    // use dummy string where no data
    if( dwRecLen == 0 )
    {
        lpszRec = szNullReplacer;
        dwRecLen = nLenNullReplacer;
    }

    for( nAttempts = 0; (nAttempts <= MAX_HASH_ATTEMPTS) && !bGenerated; nAttempts++ )
    {
        // Loop around every byte in the record
        for( lRecByteCount = lRecByteIndex = 0L; lRecByteCount < dwRecLen; lRecByteIndex++ )
        {
            // Isolate each byte in turn
            cRecByte = lpszRec[ lRecByteCount++ ] & 0x00FF;

            if( m_fText )   // If text

Answer 1

I see multiple separate problems here:

1. Array indices are always int

   long l = 0;
   int[] i = new int[] { 1, 2, 3 };
   int res1 = i[l]; //Error: Type mismatch: cannot convert from long to int
   int res2 = i[(int)l]; //works
   

2. Strings can not be directly accessed as arrays - you need to either convert it to an array first or use an accessor:

   String testString = "TESTSTRING";
   char c1 = testString[0]; //Error: The type of the expression must be an array type but it resolved to String  
   char c2 = testString.charAt(0); //works
   

3. The result of an operation between a char and an int is an int - you need to cast explicitly if you want to store it as a char:

   char c = 'h';
   char var1 = c & 0x00FF; //Error: Type mismatch: cannot convert from int to char
   char var2 = (char) (c & 0x00FF); //works