kernel.jar is a component in iText Java library to provide low-level functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided together with the JAR file in the binary packge like iText7-Core-7.1.4.zip. You can download it at iText 7 Core Download site.

You can compile it to generate your JAR file, using kernel.pom as the build configuration file.

The source code of kernel-7.1.4.jar is provided below:

⏎ com/itextpdf/kernel/pdf/canvas/parser/clipper/PolyTree.java

/*
 * This class is based on the C# open source freeware library Clipper:
 * http://www.angusj.com/delphi/clipper.php
 * The original classes were distributed under the Boost Software License:
 *
 * Freeware for both open source and commercial applications
 * Copyright 2010-2014 Angus Johnson
 * Boost Software License - Version 1.0 - August 17th, 2003
 *
 * Permission is hereby granted, free of charge, to any person or organization
 * obtaining a copy of the software and accompanying documentation covered by
 * this license (the "Software") to use, reproduce, display, distribute,
 * execute, and transmit the Software, and to prepare derivative works of the
 * Software, and to permit third-parties to whom the Software is furnished to
 * do so, all subject to the following:
 *
 * The copyright notices in the Software and this entire statement, including
 * the above license grant, this restriction and the following disclaimer,
 * must be included in all copies of the Software, in whole or in part, and
 * all derivative works of the Software, unless such copies or derivative
 * works are solely in the form of machine-executable object code generated by
 * a source language processor.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
 * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
 * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */
package com.itextpdf.kernel.pdf.canvas.parser.clipper;

import java.util.ArrayList;
import java.util.List;

public class PolyTree extends PolyNode {
    private final List<PolyNode> allPolys = new ArrayList<>();

    public void Clear() {
        allPolys.clear();
        childs.clear();
    }

    public List<PolyNode> getAllPolys() {
        return allPolys;
    }

    public PolyNode getFirst() {
        if (!childs.isEmpty()) {
            return childs.get( 0 );
        }
        else {
            return null;
        }
    }

    public int getTotalSize() {
        int result = allPolys.size();
        //with negative offsets, ignore the hidden outer polygon ...
        if (result > 0 && childs.get( 0 ) != allPolys.get( 0 )) {
            result--;
        }
        return result;

    }

}

⏎ com/itextpdf/kernel/pdf/canvas/parser/clipper/PolyTree.java

Or download all of them as a single archive file:

File name: kernel-7.1.4-sources.jar
File size: 1201221 bytes
Release date: 2018-10-09
Download 

⇒ iText io.jar Source Code

⇐ Download and Install iText7-Core-7.1.4.zip

⇑ Download and Install iText Java Library

⇑⇑ iText for PDF Generation