在一个字节中存储多个值

Question

I am writing a file to store information about locations on a map, for example where an object would spawn. I write an byte to the file and within the byte there would be x and y coordinates how would I parse them from the file

int typeData = stream.readByte();
int x = typeData >> 2;
int y = typeData & 3;

this is an example of what I'm wanting to achieve. What I am not sure is what would I have to do in the writing process, for example

outStream.writeByte((x << 2) + (y | 3));

This is an example, this code has not been tested and is likely wrong.

Answer 1

Beware that the byte data type is an 8-bit signed two's complement integer. Therefore, values are from -128 to +127, included.

So you are right when computing the bitwise operations with int variables (x and y), like that: (x << 2) + (y | 3) . Then you can cast to a byte or let Java automatically cast the result, only at the final step when calling writeByte().

You certainly need more that 8 bits to store your coordinates. To access to binary data stored in your file, remember that the initial order of a byte buffer is always BIG_ENDIAN when using the standard Java java.nio.ByteBuffer API.