I`m trying to improve my binary IO skills and thus am writing a simple utility that reads a mobi formatted ebook and prints the first 32 bytes in order to display the name of the book.

The Palm Database Format states that the first 32 bytes of the binary file contains the database/book name, and that this name is 0 terminated.

I am not sure how to check if the byte I read is null terminated.

File file = new File("ebook.mobi");
DataInputStream in = new DataInputStream(new FileInputStream(file));

int count = 1;
while(count++ <= 32){
    System.out.print((char)in.readByte());
}
in.close();

In this case the output prints:

Program_or_Be_Programmed <--- this is immediately followed by a number of square symbols

I attempted to change the while loop to no avail:

while(count++ < 32 || in.readByte != 0)

I want to add some statement to stop the loop printing characters when it encounters a 0 byte.

How would I implement this?

This is the code you said you attempted:

while(count++ <= 32 || in.readByte != 0){
    System.out.print((char)in.readByte());
}

The DataInputStream is being read twice, once in the while boolean check and again in the body.

Try:

byte b = 0;
while(++count < 32 && (b=in.readByte()) != 0){
    System.out.print((char)b);
}

Note that ++count is less resource intensive than count++ since it does not create a duplicate.

To answer your question about null bytes: null in ascii (NUL), '\0' when displayed as a symbol, is represented by the value 0. It is the end of line (EOL) character and is appended to Strings automatically.

More specifically:

char c = '\0';
byte b = (byte) c; //b == 0

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