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/gui/SystemFontMetrics.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.gui;

import java.awt.*;
import java.awt.font.FontRenderContext;
import java.awt.font.TextLayout;
import java.awt.image.BufferedImage;

/**
 *
 * @author Sam Harwell
 */
public class SystemFontMetrics extends BasicFontMetrics {
	protected final Font font;

	public SystemFontMetrics(String fontName) {
		BufferedImage img = new BufferedImage(40, 40, BufferedImage.TYPE_4BYTE_ABGR);
		Graphics2D graphics = GraphicsEnvironment.getLocalGraphicsEnvironment().createGraphics(img);
		FontRenderContext fontRenderContext = graphics.getFontRenderContext();
		this.font = new Font(fontName, Font.PLAIN, 1000);
		double maxHeight = 0;
		for (int i = 0; i < 255; i++) {
			TextLayout layout = new TextLayout(Character.toString((char)i), font, fontRenderContext);
			maxHeight = Math.max(maxHeight, layout.getBounds().getHeight());
			super.widths[i] = (int)layout.getAdvance();
		}

		super.maxCharHeight = (int)Math.round(maxHeight);
	}

	public Font getFont() {
		return font;
	}
}

⏎ org/antlr/v4/gui/SystemFontMetrics.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