Java I/O

Byte Array Streams

It’s sometimes convenient to use stream methods to manipulate data in byte arrays. For example, you might receive an array of raw bytes that you want to interpret as double-precision, floating-point numbers. (This is common when using UDP to transfer data across the Internet, for one example.) The quickest way to do this is to use a DataInputStream. However, before you can create a data input stream, you first need to create a raw, byte-oriented stream. This is what the java.io.ByteArrayInputStream class gives you. Similarly, you might want to send a group of double-precision, floating-point numbers across the network with UDP. Before you can do this, you have to convert the numbers into bytes. The simplest solution is to use a data output stream chained to a java.io.ByteArrayOutputStream. By chaining the data output stream to a byte array output stream, you can write the binary form of the floating-point numbers into a byte array, then send the entire array in a single packet.

UDP

Byte array input and output streams are commonly used when sending and receiving UDP data over the Internet. Unlike the more common TCP data, which acts like the streams I discuss in this book, UDP data arrives in raw packets of bytes, which do not necessarily have any relation to the previous packet or the next packet. Each packet is just a group of bytes to be processed in isolation from other packets. Thus, you may get nothing for several seconds, or even minutes, and then suddenly ...