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The ANTLR 4 Runtime
There is a newer version: 4.9.0
/*
 * [The "BSD license"]
 *  Copyright (c) 2012 Terence Parr
 *  Copyright (c) 2012 Sam Harwell
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.antlr.v4.runtime.atn;

import org.antlr.v4.runtime.dfa.DFA;
import org.antlr.v4.runtime.misc.Args;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.runtime.misc.NotNull;
import org.antlr.v4.runtime.misc.Nullable;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/** */
public class ATN {
	public static final int INVALID_ALT_NUMBER = 0;

	public static final int PARSER = 1;
	public static final int LEXER = 2;

	@NotNull
	public final List states = new ArrayList();

	/** Each subrule/rule is a decision point and we must track them so we
	 *  can go back later and build DFA predictors for them.  This includes
	 *  all the rules, subrules, optional blocks, ()+, ()* etc...
	 */
	@NotNull
	public final List decisionToState = new ArrayList();

	public RuleStartState[] ruleToStartState;
	public RuleStopState[] ruleToStopState;

	@NotNull
	public final Map modeNameToStartState =
		new LinkedHashMap();

	// runtime for parsers, lexers
	public int grammarType; // ATN.LEXER, ...
	public int maxTokenType;

	// runtime for lexer only
	public int[] ruleToTokenType;
	public int[] ruleToActionIndex;

	@NotNull
	public final List modeToStartState = new ArrayList();

	/** used during construction from grammar AST */
	int stateNumber = 0;

	private final ConcurrentMap contextCache =
		new ConcurrentHashMap();

	@NotNull
	public DFA[] decisionToDFA = new DFA[0];
	@NotNull
	public DFA[] modeToDFA = new DFA[0];

	protected final ConcurrentMap LL1Table = new ConcurrentHashMap();

	/** Used for runtime deserialization of ATNs from strings */
	public ATN() { }

	public final void clearDFA() {
		decisionToDFA = new DFA[decisionToState.size()];
		for (int i = 0; i < decisionToDFA.length; i++) {
			decisionToDFA[i] = new DFA(decisionToState.get(i), i);
		}

		modeToDFA = new DFA[modeToStartState.size()];
		for (int i = 0; i < modeToDFA.length; i++) {
			modeToDFA[i] = new DFA(modeToStartState.get(i));
		}

		contextCache.clear();
		LL1Table.clear();
	}

	public int getContextCacheSize() {
		return contextCache.size();
	}

	public PredictionContext getCachedContext(PredictionContext context) {
		return PredictionContext.getCachedContext(context, contextCache, new PredictionContext.IdentityHashMap());
	}

	public final DFA[] getDecisionToDFA() {
		assert decisionToDFA != null && decisionToDFA.length == decisionToState.size();
		return decisionToDFA;
	}

	/** Compute the set of valid tokens that can occur starting in s.
	 *  If ctx is {@link PredictionContext#EMPTY_LOCAL}, the set of tokens will not include what can follow
	 *  the rule surrounding s. In other words, the set will be
	 *  restricted to tokens reachable staying within s's rule.
	 */
	public IntervalSet nextTokens(ATNState s, @NotNull PredictionContext ctx) {
		Args.notNull("ctx", ctx);
		LL1Analyzer anal = new LL1Analyzer(this);
		IntervalSet next = anal.LOOK(s, ctx);
		return next;
	}

    /** Compute the set of valid tokens that can occur starting in s and staying in same rule.
     *  EPSILON is in set if we reach end of rule.
     */
    public IntervalSet nextTokens(ATNState s) {
        if ( s.nextTokenWithinRule != null ) return s.nextTokenWithinRule;
        s.nextTokenWithinRule = nextTokens(s, PredictionContext.EMPTY_LOCAL);
        s.nextTokenWithinRule.setReadonly(true);
        return s.nextTokenWithinRule;
    }

	public void addState(@Nullable ATNState state) {
		if ( state==null ) { states.add(null); stateNumber++; return; }
		state.atn = this;
		states.add(state);
		state.stateNumber = stateNumber++;
	}

	public void removeState(@NotNull ATNState state) {
		states.set(state.stateNumber, null); // just free mem, don't shift states in list
	}

	public void defineMode(@NotNull String name, @NotNull TokensStartState s) {
		modeNameToStartState.put(name, s);
		modeToStartState.add(s);
		modeToDFA = Arrays.copyOf(modeToDFA, modeToStartState.size());
		modeToDFA[modeToDFA.length - 1] = new DFA(s);
		defineDecisionState(s);
	}

	public int defineDecisionState(@NotNull DecisionState s) {
		decisionToState.add(s);
		s.decision = decisionToState.size()-1;
		decisionToDFA = Arrays.copyOf(decisionToDFA, decisionToState.size());
		decisionToDFA[decisionToDFA.length - 1] = new DFA(s, s.decision);
		return s.decision;
	}

    public DecisionState getDecisionState(int decision) {
        if ( !decisionToState.isEmpty() ) {
            return decisionToState.get(decision);
        }
        return null;
    }

	public int getNumberOfDecisions() {
		return decisionToState.size();
	}
}