StringBuilder vs Ropes

Good morning,

I am writing a language parser, and am looking for the best structure to use for a rollback cache which currently does the following:

• When requesting a new character from the stream, the character is added to the cache, in case a rollback is requested.
• When a rollback is requested, go back to a certain point in the cache so that when another character is requested, it gets it from there instead.
• When a token is found, remove everything in the rollback cache up to the current position.

So in short, I would love to know which you feel to be the best dat开发者_如何转开发a structure for:

• Priority 1: appending characters (codePoints would be a welcome addition)
• Priority 2: Doing a substring (such as StringBuilder.delete(...)) on the data structure (or clearing completely)
• Priority 3: Being able to create a string of the cache (e.g. StringBuilder.toString())

I hope to hear from you soon!

---

If I were you, for such a specialised use and with possible performance and resource constraints, I'd implement my own buffer from primitives. I think it's more trouble adapting existing structures. Of course, if it didn't hurt, I'd try to conform to the well known relevant interfaces, such as CharSequence, Appendable, List, etc.

---

I suspect that a combination of a StringBuilder and PushbackReader will give you what you need. Use the StringBuilder to accumulate characters and create token Strings, and the PushbackReader's mark and reset methods to implement rollback.

Alternatively, pre-read the entire input file as a String and then implement the tokenizer by indexing the String and taking substrings.