# Automata - Automaton Library / State Machine

### Table of Contents

## About

This page lists state machine libraries.

## List

### Regular expression library

All regular expression library implements an automaton.

We list a couple of example.

#### Automaton Library

http://www.brics.dk/automaton/ : Finite-state automaton for regular expressions.

This package uses deterministic finite-state automata (DFA), unlike most other regexp-packages that are based on nondeterministic automata (NFA). This means:

- The notion of
**regular expressions**used here has exactly the expressiveness of good old regular languages. - This package supports operations such as complement (the ~ operator) and intersection (the & operator).
- The * operator is mathematically the Kleen Star (i.e. we don't have greedy/reluctant/possessive variants).
- The time for pattern matching is optimal: once the regular expression has been converted into an automaton, it takes linear time in the length of a string to check whether it matches the expression - independently of the complexity of the expression. (NFA-based packages use backtracking.)
- There is no support for capturing groups.

Example:

```
RegExp r = new RegExp("ab(c|d)*");
Automaton a = r.toAutomaton();
String s = "abcccdc";
System.out.println("Match: " + a.run(s)); // prints: true
```

#### Multiregexp

multiregexp based on automaton

### Stateless

stateless ^{1)} Create state machines and lightweight state machine-based workflows directly in java code.

^{1)}