Package org.apache.lucene.util.automaton

# Class Operations

java.lang.Object
org.apache.lucene.util.automaton.Operations

public final class Operations extends Object
Automata operations.

WARNING: This API is experimental and might change in incompatible ways in the next release.

## Field Summary

Fields
Modifier and Type
Field
Description
`static final int`
`DEFAULT_DETERMINIZE_WORK_LIMIT`
Default maximum effort that `determinize(org.apache.lucene.util.automaton.Automaton, int)` should spend before giving up and throwing `TooComplexToDeterminizeException`.

## Method Summary

Modifier and Type
Method
Description
`static Automaton`
`complement(Automaton a, int determinizeWorkLimit)`
Returns a (deterministic) automaton that accepts the complement of the language of the given automaton.
`static Automaton`
`concatenate(List<Automaton> l)`
Returns an automaton that accepts the concatenation of the languages of the given automata.
`static Automaton`
`concatenate(Automaton a1, Automaton a2)`
Returns an automaton that accepts the concatenation of the languages of the given automata.
`static Automaton`
`determinize(Automaton a, int workLimit)`
Determinizes the given automaton.
`static String`
`getCommonPrefix(Automaton a)`
Returns the longest string that is a prefix of all accepted strings and visits each state at most once.
`static BytesRef`
`getCommonPrefixBytesRef(Automaton a)`
Returns the longest BytesRef that is a prefix of all accepted strings and visits each state at most once.
`static BytesRef`
`getCommonSuffixBytesRef(Automaton a)`
Returns the longest BytesRef that is a suffix of all accepted strings.
`static IntsRef`
`getSingleton(Automaton a)`
If this automaton accepts a single input, return it.
`static boolean`
`hasDeadStates(Automaton a)`
Returns true if this automaton has any states that cannot be reached from the initial state or cannot reach an accept state.
`static boolean`
`hasDeadStatesFromInitial(Automaton a)`
Returns true if there are dead states reachable from an initial state.
`static boolean`
`hasDeadStatesToAccept(Automaton a)`
Returns true if there are dead states that reach an accept state.
`static Automaton`
`intersection(Automaton a1, Automaton a2)`
Returns an automaton that accepts the intersection of the languages of the given automata.
`static boolean`
`isEmpty(Automaton a)`
Returns true if the given automaton accepts no strings.
`static boolean`
`isTotal(Automaton a)`
Returns true if the given automaton accepts all strings.
`static boolean`
`isTotal(Automaton a, int minAlphabet, int maxAlphabet)`
Returns true if the given automaton accepts all strings for the specified min/max range of the alphabet.
`static Automaton`
`minus(Automaton a1, Automaton a2, int determinizeWorkLimit)`
Returns a (deterministic) automaton that accepts the intersection of the language of `a1` and the complement of the language of `a2`.
`static Automaton`
`optional(Automaton a)`
Returns an automaton that accepts the union of the empty string and the language of the given automaton.
`static Automaton`
`removeDeadStates(Automaton a)`
Removes transitions to dead states (a state is "dead" if it is not reachable from the initial state or no accept state is reachable from it.)
`static Automaton`
`repeat(Automaton a)`
Returns an automaton that accepts the Kleene star (zero or more concatenated repetitions) of the language of the given automaton.
`static Automaton`
`repeat(Automaton a, int count)`
Returns an automaton that accepts `min` or more concatenated repetitions of the language of the given automaton.
`static Automaton`
`repeat(Automaton a, int min, int max)`
Returns an automaton that accepts between `min` and `max` (including both) concatenated repetitions of the language of the given automaton.
`static Automaton`
`reverse(Automaton a)`
Returns an automaton accepting the reverse language.
`static Automaton`
`reverse(Automaton a, Set<Integer> initialStates)`
Reverses the automaton, returning the new initial states.
`static boolean`
`run(Automaton a, String s)`
Returns true if the given string is accepted by the automaton.
`static boolean`
`run(Automaton a, IntsRef s)`
Returns true if the given string (expressed as unicode codepoints) is accepted by the automaton.
`static int[]`
`topoSortStates(Automaton a)`
Returns the topological sort of all states reachable from the initial state.
`static Automaton`
`union(Collection<Automaton> l)`
Returns an automaton that accepts the union of the languages of the given automata.
`static Automaton`
`union(Automaton a1, Automaton a2)`
Returns an automaton that accepts the union of the languages of the given automata.

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

## Field Details

### DEFAULT_DETERMINIZE_WORK_LIMIT

public static final int DEFAULT_DETERMINIZE_WORK_LIMIT
Default maximum effort that `determinize(org.apache.lucene.util.automaton.Automaton, int)` should spend before giving up and throwing `TooComplexToDeterminizeException`.

See Also:
  - Constant Field Values

## Method Details

### concatenate

public static Automaton concatenate(Automaton a1, Automaton a2)
Returns an automaton that accepts the concatenation of the languages of the given automata.

Complexity: linear in total number of states.

### concatenate

public static Automaton concatenate(List<Automaton> l)
Returns an automaton that accepts the concatenation of the languages of the given automata.

Complexity: linear in total number of states.

### optional

public static Automaton optional(Automaton a)
Returns an automaton that accepts the union of the empty string and the language of the given automaton. This may create a dead state.

Complexity: linear in number of states.

### repeat

public static Automaton repeat(Automaton a)
Returns an automaton that accepts the Kleene star (zero or more concatenated repetitions) of the language of the given automaton. Never modifies the input automaton language.

Complexity: linear in number of states.

### repeat

public static Automaton repeat(Automaton a, int count)
Returns an automaton that accepts `min` or more concatenated repetitions of the language of the given automaton.

Complexity: linear in number of states and in `min`.

### repeat

public static Automaton repeat(Automaton a, int min, int max)
Returns an automaton that accepts between `min` and `max` (including both) concatenated repetitions of the language of the given automaton.

Complexity: linear in number of states and in `min` and `max`.

### complement

public static Automaton complement(Automaton a, int determinizeWorkLimit)
Returns a (deterministic) automaton that accepts the complement of the language of the given automaton.

Complexity: linear in number of states if already deterministic and exponential otherwise.

Parameters:
  `determinizeWorkLimit` - maximum effort to spend determinizing the automaton. Set higher to allow more complex queries and lower to prevent memory exhaustion. `DEFAULT_DETERMINIZE_WORK_LIMIT` is a good starting default.

### minus

public static Automaton minus(Automaton a1, Automaton a2, int determinizeWorkLimit)
Returns a (deterministic) automaton that accepts the intersection of the language of `a1` and the complement of the language of `a2`. As a side-effect, the automata may be determinized, if not already deterministic.

Complexity: quadratic in number of states if a2 already deterministic and exponential in number of a2's states otherwise.

Parameters:
  `a1` - the initial automaton
  `a2` - the automaton to subtract
  `determinizeWorkLimit` - maximum effort to spend determinizing the automaton. Set higher to allow more complex queries and lower to prevent memory exhaustion. `DEFAULT_DETERMINIZE_WORK_LIMIT` is a good starting default.

### intersection

public static Automaton intersection(Automaton a1, Automaton a2)
Returns an automaton that accepts the intersection of the languages of the given automata. Never modifies the input automata languages.

Complexity: quadratic in number of states.

### hasDeadStates

public static boolean hasDeadStates(Automaton a)
Returns true if this automaton has any states that cannot be reached from the initial state or cannot reach an accept state. Cost is O(numTransitions+numStates).

### hasDeadStatesFromInitial

public static boolean hasDeadStatesFromInitial(Automaton a)
Returns true if there are dead states reachable from an initial state.

### hasDeadStatesToAccept

public static boolean hasDeadStatesToAccept(Automaton a)
Returns true if there are dead states that reach an accept state.

### union

public static Automaton union(Automaton a1, Automaton a2)
Returns an automaton that accepts the union of the languages of the given automata.

Complexity: linear in number of states.

### union

public static Automaton union(Collection<Automaton> l)
Returns an automaton that accepts the union of the languages of the given automata.

Complexity: linear in number of states.

### determinize

public static Automaton determinize(Automaton a, int workLimit)
Determinizes the given automaton.

Worst case complexity: exponential in number of states.

Parameters:
  `workLimit` - Maximum amount of "work" that the powerset construction will spend before throwing `TooComplexToDeterminizeException`. Higher numbers allow this operation to consume more memory and CPU but allow more complex automatons. Use `DEFAULT_DETERMINIZE_WORK_LIMIT` as a decent default if you don't otherwise know what to specify.
Throws:
  `TooComplexToDeterminizeException` - if determinizing requires more than `workLimit` "effort"

### isEmpty

public static boolean isEmpty(Automaton a)
Returns true if the given automaton accepts no strings.

### isTotal

public static boolean isTotal(Automaton a)
Returns true if the given automaton accepts all strings.

The automaton must be deterministic, or this method may return false.

Complexity: linear in number of states and transitions.

### isTotal

public static boolean isTotal(Automaton a, int minAlphabet, int maxAlphabet)
Returns true if the given automaton accepts all strings for the specified min/max range of the alphabet.

The automaton must be deterministic, or this method may return false.

Complexity: linear in number of states and transitions.

### run

public static boolean run(Automaton a, String s)
Returns true if the given string is accepted by the automaton. The input must be deterministic.

Complexity: linear in the length of the string.

Note: for full performance, use the `RunAutomaton` class.

### run

public static boolean run(Automaton a, IntsRef s)
Returns true if the given string (expressed as unicode codepoints) is accepted by the automaton. The input must be deterministic.

Complexity: linear in the length of the string.

Note: for full performance, use the `RunAutomaton` class.

### removeDeadStates

public static Automaton removeDeadStates(Automaton a)
Removes transitions to dead states (a state is "dead" if it is not reachable from the initial state or no accept state is reachable from it.)

### getCommonPrefix

public static String getCommonPrefix(Automaton a)
Returns the longest string that is a prefix of all accepted strings and visits each state at most once. The automaton must not have dead states. If this automaton has already been converted to UTF-8 (e.g. using `UTF32ToUTF8`) then you should use `getCommonPrefixBytesRef(org.apache.lucene.util.automaton.Automaton)` instead.

Returns:
  common prefix, which can be an empty (length 0) String (never null)
Throws:
  `IllegalArgumentException` - if the automaton has dead states reachable from the initial state.

### getCommonPrefixBytesRef

public static BytesRef getCommonPrefixBytesRef(Automaton a)
Returns the longest BytesRef that is a prefix of all accepted strings and visits each state at most once.

Returns:
  common prefix, which can be an empty (length 0) BytesRef (never null), and might possibly include a UTF-8 fragment of a full Unicode character

### getSingleton

public static IntsRef getSingleton(Automaton a)
If this automaton accepts a single input, return it. Else, return null. The automaton must be deterministic.

### getCommonSuffixBytesRef

public static BytesRef getCommonSuffixBytesRef(Automaton a)
Returns the longest BytesRef that is a suffix of all accepted strings. Worst case complexity: quadratic with number of states+transitions.

Returns:
  common suffix, which can be an empty (length 0) BytesRef (never null)

### reverse

public static Automaton reverse(Automaton a)
Returns an automaton accepting the reverse language.

### reverse

public static Automaton reverse(Automaton a, Set<Integer> initialStates)
Reverses the automaton, returning the new initial states.

### topoSortStates

public static int[] topoSortStates(Automaton a)
Returns the topological sort of all states reachable from the initial state. This method assumes that the automaton does not contain cycles, and will throw an IllegalArgumentException if a cycle is detected. The CPU cost is O(numTransitions), and the implementation is non-recursive, so it will not exhaust the java stack for automaton matching long strings. If there are dead states in the automaton, they will be removed from the returned array.

Note: This method uses a deque to iterative the states, which could potentially consume a lot of heap space for some automatons. Specifically, automatons with a deep level of states (i.e., a large number of transitions from the initial state to the final state) may particularly contribute to high memory usage. The memory consumption of this method can be considered as O(N), where N is the depth of the automaton (the maximum number of transitions from the initial state to any state). However, as this method detects cycles, it will never attempt to use infinite RAM.

Parameters:
  `a` - the Automaton to be sorted
Returns:
  the topologically sorted array of state ids