org.antlr.v4.runtime.dfa

Class DFAState

java.lang.Object

org.antlr.v4.runtime.dfa.DFAState

public class DFAState
extends Object

A DFA state represents a set of possible ATN configurations. As Aho, Sethi, Ullman p. 117 says "The DFA uses its state to keep track of all possible states the ATN can be in after reading each input symbol. That is to say, after reading input a1a2..an, the DFA is in a state that represents the subset T of the states of the ATN that are reachable from the ATN's start state along some path labeled a1a2..an." In conventional NFA→DFA conversion, therefore, the subset T would be a bitset representing the set of states the ATN could be in. We need to track the alt predicted by each state as well, however. More importantly, we need to maintain a stack of states, tracking the closure operations as they jump from rule to rule, emulating rule invocations (method calls). I have to add a stack to simulate the proper lookahead sequences for the underlying LL grammar from which the ATN was derived.

I use a set of ATNConfig objects not simple states. An ATNConfig is both a state (ala normal conversion) and a RuleContext describing the chain of rules (if any) followed to arrive at that state.

A DFA state may have multiple references to a particular state, but with different ATN contexts (with same or different alts) meaning that state was reached via a different set of rule invocations.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DFAState.PredPrediction Map a predicate to a predicted alternative.

Field Summary

Fields

Modifier and Type	Field and Description
ATNConfigSet	configs
DFAState.PredPrediction[]	predicates This list is computed by ParserATNSimulator.predicateDFAState(org.antlr.v4.runtime.dfa.DFAState, org.antlr.v4.runtime.atn.ATNConfigSet, int).
int	stateNumber

Constructor Summary

Constructors

Constructor and Description
DFAState(DFA dfa, ATNConfigSet configs) Constructs a new DFAState for a DFA.
DFAState(EmptyEdgeMap<DFAState> emptyEdges, EmptyEdgeMap<DFAState> emptyContextEdges, ATNConfigSet configs) Constructs a new DFAState with explicit initial values for the outgoing edge and context edge maps.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object o) Two DFAState instances are equal if their ATN configuration sets are the same.
AcceptStateInfo	getAcceptStateInfo()
Map<Integer,DFAState>	getContextEdgeMap()
DFAState	getContextTarget(int invokingState)
Map<Integer,DFAState>	getEdgeMap()
LexerActionExecutor	getLexerActionExecutor()
int	getPrediction()
DFAState	getTarget(int symbol)
int	hashCode()
boolean	isAcceptState()
boolean	isContextSensitive()
boolean	isContextSymbol(int symbol)
void	setAcceptState(AcceptStateInfo acceptStateInfo)
void	setContextSensitive(ATN atn)
void	setContextSymbol(int symbol)
void	setContextTarget(int invokingState, DFAState target)
void	setTarget(int symbol, DFAState target)
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

stateNumber

public int stateNumber

configs

@NotNull
public final ATNConfigSet configs

predicates

@Nullable
public DFAState.PredPrediction[] predicates

This list is computed by ParserATNSimulator.predicateDFAState(org.antlr.v4.runtime.dfa.DFAState, org.antlr.v4.runtime.atn.ATNConfigSet, int).

Constructor Detail

DFAState

public DFAState(@NotNull
        DFA dfa,
        @NotNull
        ATNConfigSet configs)

Constructs a new DFAState for a DFA.

This constructor initializes the DFA state using empty edge maps provided by the specified DFA.

Parameters:

dfa - The DFA.

configs - The set of ATN configurations defining this state.

DFAState

public DFAState(@NotNull
        EmptyEdgeMap<DFAState> emptyEdges,
        @NotNull
        EmptyEdgeMap<DFAState> emptyContextEdges,
        @NotNull
        ATNConfigSet configs)

Constructs a new DFAState with explicit initial values for the outgoing edge and context edge maps.

The empty maps provided to this constructor contain information about the range of edge values which are allowed to be stored in the map. Since edges outside the allowed range are simply dropped from the DFA, this offers several potential benefits:

• In the general case, empty edge maps are initialized to support the range of values expected to be seen during prediction, which is in turn used to minimize the memory overhead associated with a dynamically-constructed DFA.
• As a special case, empty edge maps can be intentionally constructed so the DFA will not store edges with specific values. In the limit, a range which does not contain any allowed edges can be used to prevent the DFA from storing any edges, forcing the prediction algorithm to recompute all transitions as they are needed.

Parameters:

emptyEdges - The empty edge map.

emptyContextEdges - The empty context edge map.

configs - The set of ATN configurations defining this state.

Method Detail

isContextSensitive

public final boolean isContextSensitive()

isContextSymbol

public final boolean isContextSymbol(int symbol)

setContextSymbol

public final void setContextSymbol(int symbol)

setContextSensitive

public void setContextSensitive(ATN atn)

getAcceptStateInfo

public final AcceptStateInfo getAcceptStateInfo()

setAcceptState

public final void setAcceptState(AcceptStateInfo acceptStateInfo)

isAcceptState

public final boolean isAcceptState()

getPrediction

public final int getPrediction()

getLexerActionExecutor

public final LexerActionExecutor getLexerActionExecutor()

getTarget

public DFAState getTarget(int symbol)

setTarget

public void setTarget(int symbol,
             DFAState target)

getEdgeMap

public Map<Integer,DFAState> getEdgeMap()

getContextTarget

public DFAState getContextTarget(int invokingState)

setContextTarget

public void setContextTarget(int invokingState,
                    DFAState target)

getContextEdgeMap

public Map<Integer,DFAState> getContextEdgeMap()

hashCode

public int hashCode()

Overrides:

hashCode in class Object

equals

public boolean equals(Object o)

Two DFAState instances are equal if their ATN configuration sets are the same. This method is used to see if a state already exists.

Because the number of alternatives and number of ATN configurations are finite, there is a finite number of DFA states that can be processed. This is necessary to show that the algorithm terminates.

Cannot test the DFA state numbers here because in ParserATNSimulator.addDFAState(org.antlr.v4.runtime.dfa.DFA, org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.atn.PredictionContextCache) we need to know if any other state exists that has this exact set of ATN configurations. The stateNumber is irrelevant.

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object