Automata - Automaton Library

> Automata

Table of Contents

1 - List

1.1 - Automaton

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/possesive 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
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