Java Sending data through a socket - why do I need to put a newline at the end of a String?

So, while I now get why the Outputstream connected to a socket needs to be flushed when data should be sent immediately, I still don't get why I need to put a newline at the end of the String.

This works:

// writ开发者_C百科er is a PrintWriter
writer.println("Hello World!");

This doesn't:

Writer.print("Hello World!");
writer.flush;

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You should define work and doesn't work more precisely. What's the protocol between the client and the server? What do you expect to happen and what do you observe?

I suspect the server is simply waiting for a newline character to appear in its input before doing anything. If that's the case, then of course flushing the writer at client side before sending the newline won't help.

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If you are reading with a BufferedReaders readLine method as per your previous question, readLine won't complete unless it finds the newline character(s).