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 and Inner Type Summary

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

Field Summary

Modifier and Type	Field and Description
private AcceptStateInfo	acceptStateInfo
public final ATNConfigSet	configs
private volatile AbstractEdgeMap<DFAState>	contextEdges These keys for these edges are the top level element of the global context.
private BitSet	contextSymbols Symbols in this set require a global context transition before matching an input symbol.
private volatile AbstractEdgeMap<DFAState>	edges `edges.get(symbol)` points to target of symbol.
public DFAState.PredPrediction[]	predicates This list is computed by `ParserATNSimulator#predicateDFAState`.
public int	stateNumber

Constructor Summary

Access	Constructor and Description
public	DFAState(DFA The DFA. dfa, ATNConfigSet The set of ATN configurations defining this state. configs) Constructs a new `DFAState` for a DFA.
public	DFAState(EmptyEdgeMap<DFAState> The empty edge map. emptyEdges, EmptyEdgeMap<DFAState> The empty context edge map. emptyContextEdges, ATNConfigSet The set of ATN configurations defining this state. configs) Constructs a new `DFAState` with explicit initial values for the outgoing edge and context edge maps.

Method Summary

Modifier and Type	Method and Description
public boolean	equals(Object the reference object with which to compare. o) Overrides java.lang.Object.equals. Two `DFAState` instances are equal if their ATN configuration sets are the same.
public final AcceptStateInfo	getAcceptStateInfo()
public Map<Integer, DFAState>	getContextEdgeMap()
public synchronized DFAState	getContextTarget(int invokingState)
public Map<Integer, DFAState>	getEdgeMap()
public final LexerActionExecutor	getLexerActionExecutor()
public final int	getPrediction()
public DFAState	getTarget(int symbol)
public int	hashCode() Overrides java.lang.Object.hashCode. Returns a hash code value for the object.
public final boolean	isAcceptState()
public final boolean	isContextSensitive()
public final boolean	isContextSymbol(int symbol)
public final void	setAcceptState(AcceptStateInfo acceptStateInfo)
public void	setContextSensitive(ATN atn)
public final void	setContextSymbol(int symbol)
public synchronized void	setContextTarget(int invokingState, DFAState target)
public void	setTarget(int symbol, DFAState target)
public String	toString() Overrides java.lang.Object.toString. Returns a string representation of the object.

Inherited from java.lang.Object:: clone finalize getClass notify notifyAll wait wait wait

Field Detail

acceptStateInfo	back to summary
private AcceptStateInfo acceptStateInfo

configs	back to summary
public final ATNConfigSet configs Annotations @NotNull

contextEdges	back to summary
private volatile AbstractEdgeMap<DFAState> contextEdges These keys for these edges are the top level element of the global context. Annotations @NotNull

contextSymbols	back to summary
private BitSet contextSymbols Symbols in this set require a global context transition before matching an input symbol. Annotations @Nullable

edges	back to summary
private volatile AbstractEdgeMap<DFAState> edges `edges.get(symbol)` points to target of symbol. Annotations @NotNull

predicates	back to summary
public DFAState.PredPrediction[] predicates This list is computed by `ParserATNSimulator#predicateDFAState`. Annotations @Nullable

stateNumber	back to summary
public int stateNumber

Constructor Detail

DFAState back to summary

DFAState	back to summary
public DFAState(DFA dfa, 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:DFA The DFA. configs:ATNConfigSet The set of ATN configurations defining this state.

public DFAState(DFA dfa, 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:DFA: The DFA.
configs:ATNConfigSet: The set of ATN configurations defining this state.

DFAState back to summary

DFAState	back to summary
public 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. 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:EmptyEdgeMap<DFAState> The empty edge map. emptyContextEdges:EmptyEdgeMap<DFAState> The empty context edge map. configs:ATNConfigSet The set of ATN configurations defining this state.

public 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.

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:EmptyEdgeMap<DFAState>: The empty edge map.
emptyContextEdges:EmptyEdgeMap<DFAState>: The empty context edge map.
configs:ATNConfigSet: The set of ATN configurations defining this state.

Method Detail

equals back to summary

equals	back to summary
public boolean equals(Object o) Overrides java.lang.Object.equals. 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` we need to know if any other state exists that has this exact set of ATN configurations. The `stateNumber` is irrelevant. Parameters o:Object Doc from java.lang.Object.equals. the reference object with which to compare. Returns:boolean Doc from java.lang.Object.equals. `true` if this object is the same as the obj argument; `false` otherwise. Annotations @Override

public boolean equals(Object o)

Overrides java.lang.Object.equals.

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 we need to know if any other state exists that has this exact set of ATN configurations. The stateNumber is irrelevant.

Parameters

o:Object

Doc from java.lang.Object.equals.

the reference object with which to compare.

Returns:boolean

Doc from java.lang.Object.equals.

true if this object is the same as the obj argument; false otherwise.

Annotations

@Override

getAcceptStateInfo	back to summary
public final AcceptStateInfo getAcceptStateInfo()

getContextEdgeMap	back to summary
public Map<Integer, DFAState> getContextEdgeMap()

getContextTarget	back to summary
public synchronized DFAState getContextTarget(int invokingState)

getEdgeMap	back to summary
public Map<Integer, DFAState> getEdgeMap()

getLexerActionExecutor	back to summary
public final LexerActionExecutor getLexerActionExecutor()

getPrediction	back to summary
public final int getPrediction()

getTarget	back to summary
public DFAState getTarget(int symbol)

hashCode back to summary

hashCode	back to summary
public int hashCode() Overrides java.lang.Object.hashCode. Doc from java.lang.Object.hashCode. Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by `java.util.HashMap`. The general contract of `hashCode` is: Whenever it is invoked on the same object more than once during an execution of a Java application, the `hashCode` method must consistently return the same integer, provided no information used in `equals` comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. If two objects are equal according to the `equals` method, then calling the `hashCode` method on each of the two objects must produce the same integer result. It is not required that if two objects are unequal according to the `equals` method, then calling the `hashCode` method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables. Returns:int a hash code value for this object. Annotations @Override

public int hashCode()

Overrides java.lang.Object.hashCode.

Doc from java.lang.Object.hashCode.

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by java.util.HashMap.

The general contract of hashCode is:

Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
If two objects are equal according to the equals method, then calling the hashCode method on each of the two objects must produce the same integer result.
It is not required that if two objects are unequal according to the equals method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

Returns:int

a hash code value for this object.

Annotations

@Override

isAcceptState	back to summary
public final boolean isAcceptState()

isContextSensitive	back to summary
public final boolean isContextSensitive()

isContextSymbol	back to summary
public final boolean isContextSymbol(int symbol)

setAcceptState	back to summary
public final void setAcceptState(AcceptStateInfo acceptStateInfo)

setContextSensitive	back to summary
public void setContextSensitive(ATN atn)

setContextSymbol	back to summary
public final void setContextSymbol(int symbol)

setContextTarget	back to summary
public synchronized void setContextTarget(int invokingState, DFAState target)

setTarget	back to summary
public void setTarget(int symbol, DFAState target)

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Doc from java.lang.Object.toString. Returns a string representation of the object. Returns:String a string representation of the object. Annotations @Override

toString

back to summary

public String toString()

Overrides java.lang.Object.toString.

Doc from java.lang.Object.toString.

Returns a string representation of the object.

Returns:String

a string representation of the object.

Annotations

@Override

org.antlr.v4.runtime.dfa back to summary

public Class DFAState.PredPrediction

Class Inheritance

extends Object

java.lang.Object
org.antlr.v4.runtime.dfa.DFAState.PredPrediction

Map a predicate to a predicted alternative.

Field Summary

Modifier and Type	Field and Description
public int	alt
public SemanticContext	pred

Constructor Summary

Access	Constructor and Description
public	PredPrediction(SemanticContext pred, int alt)

Method Summary

Modifier and Type	Method and Description
public String	toString() Overrides java.lang.Object.toString. Returns a string representation of the object.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll wait wait wait

Field Detail

alt	back to summary
public int alt

pred	back to summary
public SemanticContext pred Annotations @NotNull

Constructor Detail

PredPrediction	back to summary
public PredPrediction(SemanticContext pred, int alt)

Method Detail

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Doc from java.lang.Object.toString. Returns a string representation of the object. Returns:String a string representation of the object. Annotations @Override

toString

back to summary

public String toString()

Overrides java.lang.Object.toString.

Doc from java.lang.Object.toString.

Returns a string representation of the object.

Returns:String

a string representation of the object.

Annotations

@Override