Question

It’s probably a stupid question but here’s the thing. I was reading this question:

Storing 1 million phone numbers

and the accepted question was what I was thinking: using a trie. In the comments Matt Ball suggested:

I think storing the phone numbers as ASCII text and compressing is a very reasonable suggestion

Problem: how do I do that in Java? And ASCII text does stand for String?

Answer 1

For in-memory storage as indicated in the question:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
OutputStreamWriter out = new OutputStreamWriter(
    new GZIPOutputStream(baos), "US-ASCII");
for(String number : numbers){
    out.write(number);
    out.write('\n');
}
byte[] data = baos.toByteArray();

But as Pete remarked: this may be good for memory efficiency, but you can’t really do anything with the data afterwards, so it’s not really very useful.