Question

I am a little confused here.

I would like to do something like this:

1. create some kind of buffer I can write into
2. clear the buffer
3. use a printf()-like function several times to append a bunch of stuff into the buffer based on some complicated calculations I only want to do once
4. use the contents of the buffer and print it to several PrintStream objects
5. repeat steps 2-4 as necessary

e.g.:

SuperBuffer sb = new SuperBuffer();   /* SuperBuffer is not a real class, so I don't know what to use here */ PrintStream[] streams = new PrintStream[N]; /* ... initialize this array to several streams ... */  while (!done) {     sb.clear();     sb.printf('something %d something %d something %d',          value1, value2, value3);     if (some_complicated_condition())         sb.printf('something else %d something else %d', value4, value5);     /* ... more printfs to sb ... */     for (PrintStream ps : streams)         ps.println(sb.getBuffer()); } 

It looks like wrapping a PrintWriter around StringWriter will do what I want for the sb object above, except there’s no clear() method. I suppose I could create a new PrintWriter and StringWriter object each time through the loop, but that seems like a pain. (in my real code I do this in several places, not just once in one loop…)

I’ve also used java.nio.CharBuffer and other NIO buffers a lot, and that seems like a promising approach, but I’m not sure how I can wrap them with an object that will give me printf() functionality.

any advice?

Answer 1

ah: I think I’ve got it. The Formatter class has a format() method that’s like printf(), and it can be constructed to wrap around any kind of object that implements Appendable. CharBuffer implements Appendable, and I can clear() or read out the contents of the CharBuffer as necessary.