Scan Char from file in Java

Question

The java project i am working on requires me to write the java equivalent of this C code:

void read_hex_char(char *filename, unsigned char *image)
{
    int     i;
    FILE   *ff;
    short  tmp_short;
    ff = fopen(filename, "r");
    for (i = 0; i < 100; i++)
    {
        fscanf(ff, "%hx", &tmp_short);
        image[i] = tmp_short;
    }
    fclose(ff);
}

I have written this Java code.

void read_hex_char(String filename, char[] image) throws IOException
{
    Scanner s=new Scanner(new BufferedReader(new FileReader(filename)));
    for(int i=0;i<100;i++)
    {
        image[i]=s.nextShort();
    }
    s.close();
 }

Is this code correct? If its not, what corrections should be done?

@KorhanÖztürk No i haven't as this is one of the initial modules. I need to build on top of this. — Rog Matthews, Mar 14 '12 at 11:42
What are you trying to achieve ? Do you want to copy the bytes from the file to the array ? — Vinze, Mar 14 '12 at 11:43
@Vinze i want to copy the hexadecimal numbers from file to the array — Rog Matthews, Mar 14 '12 at 11:45
Are you just trying to read the numbers out of the file to the char array? — Stainedart, Mar 14 '12 at 11:45
A short is a number written as text which is between "-32768" and "32767". Are you sure all your characters are written as numbers? — Peter Lawrey, Mar 14 '12 at 12:52
I think your code is worth giving a try. If u are not going to parse always only 100 and this can be dynamic you should look at using ArrayList instead of array. — Stainedart, Mar 14 '12 at 13:54

score 1 · Accepted Answer · answered Mar 14 '12 at 12:01

I would go with a FileInputStream and read byte to byte (a short is just two bytes, char is more "complex" than just a short http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html). Simple byte extraction code from my project :

public static byte[] readFile(File file) throws IOException {
    FileInputStream in = new FileInputStream(file);
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    int ch = -1;
    while ((ch = in.read()) != -1)
        bos.write(ch);
    return bos.toByteArray();
}

For your example, the simplest is to find a few samples : run the C function on it then the java one and compare the results. It should give you informations.

an alternative of course is to use commons IO method `toByteArray` — Vinze, Mar 14 '12 at 12:08

score 0 · Answer 2 · edited May 23 '17 at 12:27

Keep in mind, that java char type is pretty smart (smarter than just byte) and represents unicode character ( and reader classes perform processing of incoming byte stream into unicode characters possibly decoding or modifyiung bytes according to actual locale and charset settings ). From your source I guess that it is just actual bytes you want in memory buffer. Here is really good explanation how to do this:

Convert InputStream to byte array in Java

score 0 · Answer 3 · answered Mar 14 '12 at 12:12

For parsing hex values, you can use Short.parseShort(String s,int radix) with radix 16. In Java, char is a bit different than short, so if you intend to perform bitmap operations, short is probably the better type to use. However, note that Java doesn't have unsigned types, which may make some of the operations likely to be used in image processing (like bitwise operations) tricky.

Scan Char from file in Java

3 Answers3