ANTLR is a powerful parser generator for multiple programming languages including Java.

ANTLR contains 2 major modules:

• Runtime - For building and executing parsers/lexers generated in Java.
• Tool (The Parser Generator) - For generating parsers/lexers Java class.

ANTLR Runtime Source Code files are provided in the distribution packge (antlr4-4.10.1.zip). You can download them at ANTLR Website.

You can also browse the source code below:

⏎ org/antlr/v4/runtime/Parser.java

/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */
package org.antlr.v4.runtime;

import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNDeserializationOptions;
import org.antlr.v4.runtime.atn.ATNDeserializer;
import org.antlr.v4.runtime.atn.ATNSimulator;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.ParseInfo;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionMode;
import org.antlr.v4.runtime.atn.ProfilingATNSimulator;
import org.antlr.v4.runtime.atn.RuleTransition;
import org.antlr.v4.runtime.dfa.DFA;
import org.antlr.v4.runtime.misc.IntegerStack;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.runtime.tree.ErrorNode;
import org.antlr.v4.runtime.tree.ErrorNodeImpl;
import org.antlr.v4.runtime.tree.ParseTreeListener;
import org.antlr.v4.runtime.tree.ParseTreeWalker;
import org.antlr.v4.runtime.tree.TerminalNode;
import org.antlr.v4.runtime.tree.TerminalNodeImpl;
import org.antlr.v4.runtime.tree.pattern.ParseTreePattern;
import org.antlr.v4.runtime.tree.pattern.ParseTreePatternMatcher;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.WeakHashMap;

/** This is all the parsing support code essentially; most of it is error recovery stuff. */
public abstract class Parser extends Recognizer<Token, ParserATNSimulator> {
	public class TraceListener implements ParseTreeListener {
		@Override
		public void enterEveryRule(ParserRuleContext ctx) {
			System.out.println("enter   " + getRuleNames()[ctx.getRuleIndex()] +
							   ", LT(1)=" + _input.LT(1).getText());
		}

		@Override
		public void visitTerminal(TerminalNode node) {
			System.out.println("consume "+node.getSymbol()+" rule "+
							   getRuleNames()[_ctx.getRuleIndex()]);
		}

		@Override
		public void visitErrorNode(ErrorNode node) {
		}

		@Override
		public void exitEveryRule(ParserRuleContext ctx) {
			System.out.println("exit    "+getRuleNames()[ctx.getRuleIndex()]+
							   ", LT(1)="+_input.LT(1).getText());
		}
	}

	public static class TrimToSizeListener implements ParseTreeListener {
		public static final TrimToSizeListener INSTANCE = new TrimToSizeListener();

		@Override
		public void enterEveryRule(ParserRuleContext ctx) { }

		@Override
		public void visitTerminal(TerminalNode node) { }

		@Override
		public void visitErrorNode(ErrorNode node) {	}

		@Override
		public void exitEveryRule(ParserRuleContext ctx) {
			if (ctx.children instanceof ArrayList) {
				((ArrayList<?>)ctx.children).trimToSize();
			}
		}
	}

	/**
	 * This field holds the deserialized {@link ATN} with bypass alternatives, created
	 * lazily upon first demand. In 4.10 I changed from map<serializedATNstring, ATN>
	 * since we only need one per parser object and also it complicates other targets
	 * that don't use ATN strings.
	 *
	 * @see ATNDeserializationOptions#isGenerateRuleBypassTransitions()
	 */
	private ATN bypassAltsAtnCache;

	/**
	 * The error handling strategy for the parser. The default value is a new
	 * instance of {@link DefaultErrorStrategy}.
	 *
	 * @see #getErrorHandler
	 * @see #setErrorHandler
	 */

	protected ANTLRErrorStrategy _errHandler = new DefaultErrorStrategy();

	/**
	 * The input stream.
	 *
	 * @see #getInputStream
	 * @see #setInputStream
	 */
	protected TokenStream _input;

	protected final IntegerStack _precedenceStack;
	{
		_precedenceStack = new IntegerStack();
		_precedenceStack.push(0);
	}

	/**
	 * The {@link ParserRuleContext} object for the currently executing rule.
	 * This is always non-null during the parsing process.
	 */
	protected ParserRuleContext _ctx;

	/**
	 * Specifies whether or not the parser should construct a parse tree during
	 * the parsing process. The default value is {@code true}.
	 *
	 * @see #getBuildParseTree
	 * @see #setBuildParseTree
	 */
	protected boolean _buildParseTrees = true;


	/**
	 * When {@link #setTrace}{@code (true)} is called, a reference to the
	 * {@link TraceListener} is stored here so it can be easily removed in a
	 * later call to {@link #setTrace}{@code (false)}. The listener itself is
	 * implemented as a parser listener so this field is not directly used by
	 * other parser methods.
	 */
	private TraceListener _tracer;

	/**
	 * The list of {@link ParseTreeListener} listeners registered to receive
	 * events during the parse.
	 *
	 * @see #addParseListener
	 */
	protected List<ParseTreeListener> _parseListeners;

	/**
	 * The number of syntax errors reported during parsing. This value is
	 * incremented each time {@link #notifyErrorListeners} is called.
	 */
	protected int _syntaxErrors;

	/** Indicates parser has match()ed EOF token. See {@link #exitRule()}. */
	protected boolean matchedEOF;

	public Parser(TokenStream input) {
		setInputStream(input);
	}

	/** reset the parser's state */
	public void reset() {
		if ( getInputStream()!=null ) getInputStream().seek(0);
		_errHandler.reset(this);
		_ctx = null;
		_syntaxErrors = 0;
		matchedEOF = false;
		setTrace(false);
		_precedenceStack.clear();
		_precedenceStack.push(0);
		ATNSimulator interpreter = getInterpreter();
		if (interpreter != null) {
			interpreter.reset();
		}
	}

	/**
	 * Match current input symbol against {@code ttype}. If the symbol type
	 * matches, {@link ANTLRErrorStrategy#reportMatch} and {@link #consume} are
	 * called to complete the match process.
	 *
	 * <p>If the symbol type does not match,
	 * {@link ANTLRErrorStrategy#recoverInline} is called on the current error
	 * strategy to attempt recovery. If {@link #getBuildParseTree} is
	 * {@code true} and the token index of the symbol returned by
	 * {@link ANTLRErrorStrategy#recoverInline} is -1, the symbol is added to
	 * the parse tree by calling {@link #createErrorNode(ParserRuleContext, Token)} then
	 * {@link ParserRuleContext#addErrorNode(ErrorNode)}.</p>
	 *
	 * @param ttype the token type to match
	 * @return the matched symbol
	 * @throws RecognitionException if the current input symbol did not match
	 * {@code ttype} and the error strategy could not recover from the
	 * mismatched symbol
	 */
	public Token match(int ttype) throws RecognitionException {
		Token t = getCurrentToken();
		if ( t.getType()==ttype ) {
			if ( ttype==Token.EOF ) {
				matchedEOF = true;
			}
			_errHandler.reportMatch(this);
			consume();
		}
		else {
			t = _errHandler.recoverInline(this);
			if ( _buildParseTrees && t.getTokenIndex()==-1 ) {
				// we must have conjured up a new token during single token insertion
				// if it's not the current symbol
				_ctx.addErrorNode(createErrorNode(_ctx,t));
			}
		}
		return t;
	}

	/**
	 * Match current input symbol as a wildcard. If the symbol type matches
	 * (i.e. has a value greater than 0), {@link ANTLRErrorStrategy#reportMatch}
	 * and {@link #consume} are called to complete the match process.
	 *
	 * <p>If the symbol type does not match,
	 * {@link ANTLRErrorStrategy#recoverInline} is called on the current error
	 * strategy to attempt recovery. If {@link #getBuildParseTree} is
	 * {@code true} and the token index of the symbol returned by
	 * {@link ANTLRErrorStrategy#recoverInline} is -1, the symbol is added to
	 * the parse tree by calling {@link Parser#createErrorNode(ParserRuleContext, Token)}. then
     * {@link ParserRuleContext#addErrorNode(ErrorNode)}</p>
	 *
	 * @return the matched symbol
	 * @throws RecognitionException if the current input symbol did not match
	 * a wildcard and the error strategy could not recover from the mismatched
	 * symbol
	 */
	public Token matchWildcard() throws RecognitionException {
		Token t = getCurrentToken();
		if (t.getType() > 0) {
			_errHandler.reportMatch(this);
			consume();
		}
		else {
			t = _errHandler.recoverInline(this);
			if (_buildParseTrees && t.getTokenIndex() == -1) {
				// we must have conjured up a new token during single token insertion
				// if it's not the current symbol
				_ctx.addErrorNode(createErrorNode(_ctx,t));
			}
		}

		return t;
	}

	/**
	 * Track the {@link ParserRuleContext} objects during the parse and hook
	 * them up using the {@link ParserRuleContext#children} list so that it
	 * forms a parse tree. The {@link ParserRuleContext} returned from the start
	 * rule represents the root of the parse tree.
	 *
	 * <p>Note that if we are not building parse trees, rule contexts only point
	 * upwards. When a rule exits, it returns the context but that gets garbage
	 * collected if nobody holds a reference. It points upwards but nobody
	 * points at it.</p>
	 *
	 * <p>When we build parse trees, we are adding all of these contexts to
	 * {@link ParserRuleContext#children} list. Contexts are then not candidates
	 * for garbage collection.</p>
	 */
	public void setBuildParseTree(boolean buildParseTrees) {
		this._buildParseTrees = buildParseTrees;
	}

	/**
	 * Gets whether or not a complete parse tree will be constructed while
	 * parsing. This property is {@code true} for a newly constructed parser.
	 *
	 * @return {@code true} if a complete parse tree will be constructed while
	 * parsing, otherwise {@code false}
	 */
	public boolean getBuildParseTree() {
		return _buildParseTrees;
	}

	/**
	 * Trim the internal lists of the parse tree during parsing to conserve memory.
	 * This property is set to {@code false} by default for a newly constructed parser.
	 *
	 * @param trimParseTrees {@code true} to trim the capacity of the {@link ParserRuleContext#children}
	 * list to its size after a rule is parsed.
	 */
	public void setTrimParseTree(boolean trimParseTrees) {
		if (trimParseTrees) {
			if (getTrimParseTree()) return;
			addParseListener(TrimToSizeListener.INSTANCE);
		}
		else {
			removeParseListener(TrimToSizeListener.INSTANCE);
		}
	}

	/**
	 * @return {@code true} if the {@link ParserRuleContext#children} list is trimmed
	 * using the default {@link Parser.TrimToSizeListener} during the parse process.
	 */
	public boolean getTrimParseTree() {
		return getParseListeners().contains(TrimToSizeListener.INSTANCE);
	}


	public List<ParseTreeListener> getParseListeners() {
		List<ParseTreeListener> listeners = _parseListeners;
		if (listeners == null) {
			return Collections.emptyList();
		}

		return listeners;
	}

	/**
	 * Registers {@code listener} to receive events during the parsing process.
	 *
	 * <p>To support output-preserving grammar transformations (including but not
	 * limited to left-recursion removal, automated left-factoring, and
	 * optimized code generation), calls to listener methods during the parse
	 * may differ substantially from calls made by
	 * {@link ParseTreeWalker#DEFAULT} used after the parse is complete. In
	 * particular, rule entry and exit events may occur in a different order
	 * during the parse than after the parser. In addition, calls to certain
	 * rule entry methods may be omitted.</p>
	 *
	 * <p>With the following specific exceptions, calls to listener events are
	 * <em>deterministic</em>, i.e. for identical input the calls to listener
	 * methods will be the same.</p>
	 *
	 * <ul>
	 * <li>Alterations to the grammar used to generate code may change the
	 * behavior of the listener calls.</li>
	 * <li>Alterations to the command line options passed to ANTLR 4 when
	 * generating the parser may change the behavior of the listener calls.</li>
	 * <li>Changing the version of the ANTLR Tool used to generate the parser
	 * may change the behavior of the listener calls.</li>
	 * </ul>
	 *
	 * @param listener the listener to add
	 *
	 * @throws NullPointerException if {@code} listener is {@code null}
	 */
	public void addParseListener(ParseTreeListener listener) {
		if (listener == null) {
			throw new NullPointerException("listener");
		}

		if (_parseListeners == null) {
			_parseListeners = new ArrayList<ParseTreeListener>();
		}

		this._parseListeners.add(listener);
	}

	/**
	 * Remove {@code listener} from the list of parse listeners.
	 *
	 * <p>If {@code listener} is {@code null} or has not been added as a parse
	 * listener, this method does nothing.</p>
	 *
	 * @see #addParseListener
	 *
	 * @param listener the listener to remove
	 */
	public void removeParseListener(ParseTreeListener listener) {
		if (_parseListeners != null) {
			if (_parseListeners.remove(listener)) {
				if (_parseListeners.isEmpty()) {
					_parseListeners = null;
				}
			}
		}
	}

	/**
	 * Remove all parse listeners.
	 *
	 * @see #addParseListener
	 */
	public void removeParseListeners() {
		_parseListeners = null;
	}

	/**
	 * Notify any parse listeners of an enter rule event.
	 *
	 * @see #addParseListener
	 */
	protected void triggerEnterRuleEvent() {
		for (ParseTreeListener listener : _parseListeners) {
			listener.enterEveryRule(_ctx);
			_ctx.enterRule(listener);
		}
	}

	/**
	 * Notify any parse listeners of an exit rule event.
	 *
	 * @see #addParseListener
	 */
	protected void triggerExitRuleEvent() {
		// reverse order walk of listeners
		for (int i = _parseListeners.size()-1; i >= 0; i--) {
			ParseTreeListener listener = _parseListeners.get(i);
			_ctx.exitRule(listener);
			listener.exitEveryRule(_ctx);
		}
	}

	/**
	 * Gets the number of syntax errors reported during parsing. This value is
	 * incremented each time {@link #notifyErrorListeners} is called.
	 *
	 * @see #notifyErrorListeners
	 */
	public int getNumberOfSyntaxErrors() {
		return _syntaxErrors;
	}

	@Override
	public TokenFactory<?> getTokenFactory() {
		return _input.getTokenSource().getTokenFactory();
	}

	/** Tell our token source and error strategy about a new way to create tokens. */
	@Override
	public void setTokenFactory(TokenFactory<?> factory) {
		_input.getTokenSource().setTokenFactory(factory);
	}

	/**
	 * The ATN with bypass alternatives is expensive to create so we create it
	 * lazily.
	 *
	 * @throws UnsupportedOperationException if the current parser does not
	 * implement the {@link #getSerializedATN()} method.
	 */

	public ATN getATNWithBypassAlts() {
		String serializedAtn = getSerializedATN();
		if (serializedAtn == null) {
			throw new UnsupportedOperationException("The current parser does not support an ATN with bypass alternatives.");
		}

		synchronized (this) {
			if ( bypassAltsAtnCache!=null ) {
				return bypassAltsAtnCache;
			}
			ATNDeserializationOptions deserializationOptions = new ATNDeserializationOptions();
			deserializationOptions.setGenerateRuleBypassTransitions(true);
			bypassAltsAtnCache = new ATNDeserializer(deserializationOptions).deserialize(serializedAtn.toCharArray());
			return bypassAltsAtnCache;
		}
	}

	/**
	 * The preferred method of getting a tree pattern. For example, here's a
	 * sample use:
	 *
	 * <pre>
	 * ParseTree t = parser.expr();
	 * ParseTreePattern p = parser.compileParseTreePattern("&lt;ID&gt;+0", MyParser.RULE_expr);
	 * ParseTreeMatch m = p.match(t);
	 * String id = m.get("ID");
	 * </pre>
	 */
	public ParseTreePattern compileParseTreePattern(String pattern, int patternRuleIndex) {
		if ( getTokenStream()!=null ) {
			TokenSource tokenSource = getTokenStream().getTokenSource();
			if ( tokenSource instanceof Lexer ) {
				Lexer lexer = (Lexer)tokenSource;
				return compileParseTreePattern(pattern, patternRuleIndex, lexer);
			}
		}
		throw new UnsupportedOperationException("Parser can't discover a lexer to use");
	}

	/**
	 * The same as {@link #compileParseTreePattern(String, int)} but specify a
	 * {@link Lexer} rather than trying to deduce it from this parser.
	 */
	public ParseTreePattern compileParseTreePattern(String pattern, int patternRuleIndex,
													Lexer lexer)
	{
		ParseTreePatternMatcher m = new ParseTreePatternMatcher(lexer, this);
		return m.compile(pattern, patternRuleIndex);
	}


	public ANTLRErrorStrategy getErrorHandler() {
		return _errHandler;
	}

	public void setErrorHandler(ANTLRErrorStrategy handler) {
		this._errHandler = handler;
	}

	@Override
	public TokenStream getInputStream() { return getTokenStream(); }

	@Override
	public final void setInputStream(IntStream input) {
		setTokenStream((TokenStream)input);
	}

	public TokenStream getTokenStream() {
		return _input;
	}

	/** Set the token stream and reset the parser. */
	public void setTokenStream(TokenStream input) {
		this._input = null;
		reset();
		this._input = input;
	}

    /** Match needs to return the current input symbol, which gets put
     *  into the label for the associated token ref; e.g., x=ID.
     */

    public Token getCurrentToken() {
		return _input.LT(1);
	}

	public final void notifyErrorListeners(String msg)	{
		notifyErrorListeners(getCurrentToken(), msg, null);
	}

	public void notifyErrorListeners(Token offendingToken, String msg,
									 RecognitionException e)
	{
		_syntaxErrors++;
		int line = -1;
		int charPositionInLine = -1;
		line = offendingToken.getLine();
		charPositionInLine = offendingToken.getCharPositionInLine();

		ANTLRErrorListener listener = getErrorListenerDispatch();
		listener.syntaxError(this, offendingToken, line, charPositionInLine, msg, e);
	}

	/**
	 * Consume and return the {@linkplain #getCurrentToken current symbol}.
	 *
	 * <p>E.g., given the following input with {@code A} being the current
	 * lookahead symbol, this function moves the cursor to {@code B} and returns
	 * {@code A}.</p>
	 *
	 * <pre>
	 *  A B
	 *  ^
	 * </pre>
	 *
	 * If the parser is not in error recovery mode, the consumed symbol is added
	 * to the parse tree using {@link ParserRuleContext#addChild(TerminalNode)}, and
	 * {@link ParseTreeListener#visitTerminal} is called on any parse listeners.
	 * If the parser <em>is</em> in error recovery mode, the consumed symbol is
	 * added to the parse tree using {@link #createErrorNode(ParserRuleContext, Token)} then
     * {@link ParserRuleContext#addErrorNode(ErrorNode)} and
	 * {@link ParseTreeListener#visitErrorNode} is called on any parse
	 * listeners.
	 */
	public Token consume() {
		Token o = getCurrentToken();
		if (o.getType() != EOF) {
			getInputStream().consume();
		}
		boolean hasListener = _parseListeners != null && !_parseListeners.isEmpty();
		if (_buildParseTrees || hasListener) {
			if ( _errHandler.inErrorRecoveryMode(this) ) {
				ErrorNode node = _ctx.addErrorNode(createErrorNode(_ctx,o));
				if (_parseListeners != null) {
					for (ParseTreeListener listener : _parseListeners) {
						listener.visitErrorNode(node);
					}
				}
			}
			else {
				TerminalNode node = _ctx.addChild(createTerminalNode(_ctx,o));
				if (_parseListeners != null) {
					for (ParseTreeListener listener : _parseListeners) {
						listener.visitTerminal(node);
					}
				}
			}
		}
		return o;
	}

	/** How to create a token leaf node associated with a parent.
	 *  Typically, the terminal node to create is not a function of the parent.
	 *
	 * @since 4.7
	 */
	public TerminalNode createTerminalNode(ParserRuleContext parent, Token t) {
		return new TerminalNodeImpl(t);
	}

	/** How to create an error node, given a token, associated with a parent.
	 *  Typically, the error node to create is not a function of the parent.
	 *
	 * @since 4.7
	 */
	public ErrorNode createErrorNode(ParserRuleContext parent, Token t) {
		return new ErrorNodeImpl(t);
	}

	protected void addContextToParseTree() {
		ParserRuleContext parent = (ParserRuleContext)_ctx.parent;
		// add current context to parent if we have a parent
		if ( parent!=null )	{
			parent.addChild(_ctx);
		}
	}

	/**
	 * Always called by generated parsers upon entry to a rule. Access field
	 * {@link #_ctx} get the current context.
	 */
	public void enterRule(ParserRuleContext localctx, int state, int ruleIndex) {
		setState(state);
		_ctx = localctx;
		_ctx.start = _input.LT(1);
		if (_buildParseTrees) addContextToParseTree();
        if ( _parseListeners != null) triggerEnterRuleEvent();
	}

    public void exitRule() {
		if ( matchedEOF ) {
			// if we have matched EOF, it cannot consume past EOF so we use LT(1) here
			_ctx.stop = _input.LT(1); // LT(1) will be end of file
		}
		else {
			_ctx.stop = _input.LT(-1); // stop node is what we just matched
		}
        // trigger event on _ctx, before it reverts to parent
        if ( _parseListeners != null) triggerExitRuleEvent();
		setState(_ctx.invokingState);
		_ctx = (ParserRuleContext)_ctx.parent;
    }

	public void enterOuterAlt(ParserRuleContext localctx, int altNum) {
		localctx.setAltNumber(altNum);
		// if we have new localctx, make sure we replace existing ctx
		// that is previous child of parse tree
		if ( _buildParseTrees && _ctx != localctx ) {
			ParserRuleContext parent = (ParserRuleContext)_ctx.parent;
			if ( parent!=null )	{
				parent.removeLastChild();
				parent.addChild(localctx);
			}
		}
		_ctx = localctx;
	}

	/**
	 * Get the precedence level for the top-most precedence rule.
	 *
	 * @return The precedence level for the top-most precedence rule, or -1 if
	 * the parser context is not nested within a precedence rule.
	 */
	public final int getPrecedence() {
		if (_precedenceStack.isEmpty()) {
			return -1;
		}

		return _precedenceStack.peek();
	}

	/**
	 * @deprecated Use
	 * {@link #enterRecursionRule(ParserRuleContext, int, int, int)} instead.
	 */
	@Deprecated
	public void enterRecursionRule(ParserRuleContext localctx, int ruleIndex) {
		enterRecursionRule(localctx, getATN().ruleToStartState[ruleIndex].stateNumber, ruleIndex, 0);
	}

	public void enterRecursionRule(ParserRuleContext localctx, int state, int ruleIndex, int precedence) {
		setState(state);
		_precedenceStack.push(precedence);
		_ctx = localctx;
		_ctx.start = _input.LT(1);
		if (_parseListeners != null) {
			triggerEnterRuleEvent(); // simulates rule entry for left-recursive rules
		}
	}

	/** Like {@link #enterRule} but for recursive rules.
	 *  Make the current context the child of the incoming localctx.
	 */
	public void pushNewRecursionContext(ParserRuleContext localctx, int state, int ruleIndex) {
		ParserRuleContext previous = _ctx;
		previous.parent = localctx;
		previous.invokingState = state;
		previous.stop = _input.LT(-1);

		_ctx = localctx;
		_ctx.start = previous.start;
		if (_buildParseTrees) {
			_ctx.addChild(previous);
		}

		if ( _parseListeners != null ) {
			triggerEnterRuleEvent(); // simulates rule entry for left-recursive rules
		}
	}

	public void unrollRecursionContexts(ParserRuleContext _parentctx) {
		_precedenceStack.pop();
		_ctx.stop = _input.LT(-1);
		ParserRuleContext retctx = _ctx; // save current ctx (return value)

		// unroll so _ctx is as it was before call to recursive method
		if ( _parseListeners != null ) {
			while ( _ctx != _parentctx ) {
				triggerExitRuleEvent();
				_ctx = (ParserRuleContext)_ctx.parent;
			}
		}
		else {
			_ctx = _parentctx;
		}

		// hook into tree
		retctx.parent = _parentctx;

		if (_buildParseTrees && _parentctx != null) {
			// add return ctx into invoking rule's tree
			_parentctx.addChild(retctx);
		}
	}

	public ParserRuleContext getInvokingContext(int ruleIndex) {
		ParserRuleContext p = _ctx;
		while ( p!=null ) {
			if ( p.getRuleIndex() == ruleIndex ) return p;
			p = (ParserRuleContext)p.parent;
		}
		return null;
	}

	public ParserRuleContext getContext() {
		return _ctx;
	}

	public void setContext(ParserRuleContext ctx) {
		_ctx = ctx;
	}

	@Override
	public boolean precpred(RuleContext localctx, int precedence) {
		return precedence >= _precedenceStack.peek();
	}

	public boolean inContext(String context) {
		// TODO: useful in parser?
		return false;
	}

	/**
	 * Checks whether or not {@code symbol} can follow the current state in the
	 * ATN. The behavior of this method is equivalent to the following, but is
	 * implemented such that the complete context-sensitive follow set does not
	 * need to be explicitly constructed.
	 *
	 * <pre>
	 * return getExpectedTokens().contains(symbol);
	 * </pre>
	 *
	 * @param symbol the symbol type to check
	 * @return {@code true} if {@code symbol} can follow the current state in
	 * the ATN, otherwise {@code false}.
	 */
    public boolean isExpectedToken(int symbol) {
//   		return getInterpreter().atn.nextTokens(_ctx);
        ATN atn = getInterpreter().atn;
		ParserRuleContext ctx = _ctx;
        ATNState s = atn.states.get(getState());
        IntervalSet following = atn.nextTokens(s);
        if (following.contains(symbol)) {
            return true;
        }
//        System.out.println("following "+s+"="+following);
        if ( !following.contains(Token.EPSILON) ) return false;

        while ( ctx!=null && ctx.invokingState>=0 && following.contains(Token.EPSILON) ) {
            ATNState invokingState = atn.states.get(ctx.invokingState);
            RuleTransition rt = (RuleTransition)invokingState.transition(0);
            following = atn.nextTokens(rt.followState);
            if (following.contains(symbol)) {
                return true;
            }

            ctx = (ParserRuleContext)ctx.parent;
        }

        if ( following.contains(Token.EPSILON) && symbol == Token.EOF ) {
            return true;
        }

        return false;
    }

	public boolean isMatchedEOF() {
		return matchedEOF;
	}

	/**
	 * Computes the set of input symbols which could follow the current parser
	 * state and context, as given by {@link #getState} and {@link #getContext},
	 * respectively.
	 *
	 * @see ATN#getExpectedTokens(int, RuleContext)
	 */
	public IntervalSet getExpectedTokens() {
		return getATN().getExpectedTokens(getState(), getContext());
	}


    public IntervalSet getExpectedTokensWithinCurrentRule() {
        ATN atn = getInterpreter().atn;
        ATNState s = atn.states.get(getState());
   		return atn.nextTokens(s);
   	}

	/** Get a rule's index (i.e., {@code RULE_ruleName} field) or -1 if not found. */
	public int getRuleIndex(String ruleName) {
		Integer ruleIndex = getRuleIndexMap().get(ruleName);
		if ( ruleIndex!=null ) return ruleIndex;
		return -1;
	}

	public ParserRuleContext getRuleContext() { return _ctx; }

	/** Return List&lt;String&gt; of the rule names in your parser instance
	 *  leading up to a call to the current rule.  You could override if
	 *  you want more details such as the file/line info of where
	 *  in the ATN a rule is invoked.
	 *
	 *  This is very useful for error messages.
	 */
	public List<String> getRuleInvocationStack() {
		return getRuleInvocationStack(_ctx);
	}

	public List<String> getRuleInvocationStack(RuleContext p) {
		String[] ruleNames = getRuleNames();
		List<String> stack = new ArrayList<String>();
		while ( p!=null ) {
			// compute what follows who invoked us
			int ruleIndex = p.getRuleIndex();
			if ( ruleIndex<0 ) stack.add("n/a");
			else stack.add(ruleNames[ruleIndex]);
			p = p.parent;
		}
		return stack;
	}

	/** For debugging and other purposes. */
	public List<String> getDFAStrings() {
		synchronized (_interp.decisionToDFA) {
			List<String> s = new ArrayList<String>();
			for (int d = 0; d < _interp.decisionToDFA.length; d++) {
				DFA dfa = _interp.decisionToDFA[d];
				s.add( dfa.toString(getVocabulary()) );
			}
			return s;
		}
    }

	/** For debugging and other purposes. */
	public void dumpDFA() {
		synchronized (_interp.decisionToDFA) {
			boolean seenOne = false;
			for (int d = 0; d < _interp.decisionToDFA.length; d++) {
				DFA dfa = _interp.decisionToDFA[d];
				if ( !dfa.states.isEmpty() ) {
					if ( seenOne ) System.out.println();
					System.out.println("Decision " + dfa.decision + ":");
					System.out.print(dfa.toString(getVocabulary()));
					seenOne = true;
				}
			}
		}
    }

	public String getSourceName() {
		return _input.getSourceName();
	}

	@Override
	public ParseInfo getParseInfo() {
		ParserATNSimulator interp = getInterpreter();
		if (interp instanceof ProfilingATNSimulator) {
			return new ParseInfo((ProfilingATNSimulator)interp);
		}
		return null;
	}

	/**
	 * @since 4.3
	 */
	public void setProfile(boolean profile) {
		ParserATNSimulator interp = getInterpreter();
		PredictionMode saveMode = interp.getPredictionMode();
		if ( profile ) {
			if ( !(interp instanceof ProfilingATNSimulator) ) {
				setInterpreter(new ProfilingATNSimulator(this));
			}
		}
		else if ( interp instanceof ProfilingATNSimulator ) {
			ParserATNSimulator sim =
				new ParserATNSimulator(this, getATN(), interp.decisionToDFA, interp.getSharedContextCache());
			setInterpreter(sim);
		}
		getInterpreter().setPredictionMode(saveMode);
	}

	/** During a parse is sometimes useful to listen in on the rule entry and exit
	 *  events as well as token matches. This is for quick and dirty debugging.
	 */
	public void setTrace(boolean trace) {
		if ( !trace ) {
			removeParseListener(_tracer);
			_tracer = null;
		}
		else {
			if ( _tracer!=null ) removeParseListener(_tracer);
			else _tracer = new TraceListener();
			addParseListener(_tracer);
		}
	}

	/**
	 * Gets whether a {@link TraceListener} is registered as a parse listener
	 * for the parser.
	 *
	 * @see #setTrace(boolean)
	 */
	public boolean isTrace() {
		return _tracer != null;
	}
}

⏎ org/antlr/v4/runtime/Parser.java

Or download all of them as a single archive file:

File name: antlr-runtime-4.10.1-sources.jar
File size: 308953 bytes
Release date: 2022-04-15
Download 

⇒ ANTLR Tool Source Code

⇐ What Is ANTLR Parser Generator

⇑ Download and Review ANTLR Parser Generator

⇑⇑ FAQ for ANTLR Parser Generator