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 Tool 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/misc/FrequencySet.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.misc;

import java.util.HashMap;

/** Count how many of each key we have; not thread safe */
public class FrequencySet<T> extends HashMap<T, MutableInt> {
	public int count(T key) {
		MutableInt value = get(key);
		if (value == null) return 0;
		return value.v;
	}
	public void add(T key) {
		MutableInt value = get(key);
		if (value == null) {
			value = new MutableInt(1);
			put(key, value);
		}
		else {
			value.v++;
		}
	}
}

⏎ org/antlr/v4/misc/FrequencySet.java

Or download all of them as a single archive file:

File name: antlr-tool-4.10.1-sources.jar
File size: 347718 bytes
Release date: 2022-04-15
Download 

⇒ Donwload antlr4-4.10.1.zip

⇐ ANTLR Runtime Source Code

⇑ Download and Review ANTLR Parser Generator

⇑⇑ FAQ for ANTLR Parser Generator