Package org.apache.lucene.util.automaton

Class Automaton

  • All Implemented Interfaces:
    Cloneable
    public class Automaton
extends Object
implements Cloneable
    Finite-state automaton with regular expression operations.

    Class invariants:

    • An automaton is either represented explicitly (with State and Transition objects) or with a singleton string (see getSingleton() and expandSingleton()) in case the automaton is known to accept exactly one string. (Implicitly, all states and transitions of an automaton are reachable from its initial state.)
    • Automata are always reduced (see reduce()) and have no transitions to dead states (see removeDeadTransitions()).
    • If an automaton is nondeterministic, then isDeterministic() returns false (but the converse is not required).
    • Automata provided as input to operations are generally assumed to be disjoint.

    If the states or transitions are manipulated manually, the restoreInvariant() and setDeterministic(boolean) methods should be used afterwards to restore representation invariants that are assumed by the built-in automata operations.

    Note: This class has internal mutable state and is not thread safe. It is the caller's responsibility to ensure any necessary synchronization if you wish to use the same Automaton from multiple threads. In general it is instead recommended to use a RunAutomaton for multithreaded matching: it is immutable, thread safe, and much faster.

    • Field Detail

      • MINIMIZE_HOPCROFT

        public static final int MINIMIZE_HOPCROFT
        Minimize using Hopcroft's O(n log n) algorithm. This is regarded as one of the most generally efficient algorithms that exist.
        See Also:
        setMinimization(int), Constant Field Values

    • Constructor Detail

      • Automaton

        public Automaton​(State initial)
        Constructs a new automaton that accepts the empty language. Using this constructor, automata can be constructed manually from State and Transition objects.
        See Also:
        State, Transition

      • Automaton

        public Automaton()

    • Method Detail

      • setMinimization

        public static void setMinimization​(int algorithm)
        Selects minimization algorithm (default: MINIMIZE_HOPCROFT).
        Parameters:
        algorithm - minimization algorithm

      • setMinimizeAlways

        public static void setMinimizeAlways​(boolean flag)
        Sets or resets minimize always flag. If this flag is set, then MinimizationOperations.minimize(Automaton) will automatically be invoked after all operations that otherwise may produce non-minimal automata. By default, the flag is not set.
        Parameters:
        flag - if true, the flag is set

      • setAllowMutate

        public static boolean setAllowMutate​(boolean flag)
        Sets or resets allow mutate flag. If this flag is set, then all automata operations may modify automata given as input; otherwise, operations will always leave input automata languages unmodified. By default, the flag is not set.
        Parameters:
        flag - if true, the flag is set
        Returns:
        previous value of the flag

      • getSingleton

        public String getSingleton()
        Returns the singleton string for this automaton. An automaton that accepts exactly one string may be represented in singleton mode. In that case, this method may be used to obtain the string.
        Returns:
        string, null if this automaton is not in singleton mode.

      • getInitialState

        public State getInitialState()
        Gets initial state.
        Returns:
        state

      • isDeterministic

        public boolean isDeterministic()
        Returns deterministic flag for this automaton.
        Returns:
        true if the automaton is definitely deterministic, false if the automaton may be nondeterministic

      • setDeterministic

        public void setDeterministic​(boolean deterministic)
        Sets deterministic flag for this automaton. This method should (only) be used if automata are constructed manually.
        Parameters:
        deterministic - true if the automaton is definitely deterministic, false if the automaton may be nondeterministic

      • setInfo

        public void setInfo​(Object info)
        Associates extra information with this automaton.
        Parameters:
        info - extra information

      • getInfo

        public Object getInfo()
        Returns extra information associated with this automaton.
        Returns:
        extra information
        See Also:
        setInfo(Object)

      • getNumberedStates

        public State[] getNumberedStates()

      • setNumberedStates

        public void setNumberedStates​(State[] states)

      • setNumberedStates

        public void setNumberedStates​(State[] states,
                              int count)

      • clearNumberedStates

        public void clearNumberedStates()

      • getAcceptStates

        public Set<State> getAcceptStates()
        Returns the set of reachable accept states.
        Returns:
        set of State objects

      • restoreInvariant

        public void restoreInvariant()
        Restores representation invariant. This method must be invoked before any built-in automata operation is performed if automaton states or transitions are manipulated manually.
        See Also:
        setDeterministic(boolean)

      • reduce

        public void reduce()
        Reduces this automaton. An automaton is "reduced" by combining overlapping and adjacent edge intervals with same destination.

      • removeDeadTransitions

        public void removeDeadTransitions()
        Removes transitions to dead states and calls reduce(). (A state is "dead" if no accept state is reachable from it.)

      • getSortedTransitions

        public Transition[][] getSortedTransitions()
        Returns a sorted array of transitions for each state (and sets state numbers).

      • expandSingleton

        public void expandSingleton()
        Expands singleton representation to normal representation. Does nothing if not in singleton representation.

      • getNumberOfStates

        public int getNumberOfStates()
        Returns the number of states in this automaton.

      • getNumberOfTransitions

        public int getNumberOfTransitions()
        Returns the number of transitions in this automaton. This number is counted as the total number of edges, where one edge may be a character interval.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Object

      • toString

        public String toString()
        Returns a string representation of this automaton.
        Overrides:
        toString in class Object

      • clone

        public Automaton clone()
        Returns a clone of this automaton.
        Overrides:
        clone in class Object