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"nb-javac" is a patched version of OpenJDK "javac", i.e., the Java compiler. This has long been part of NetBeans, providing a highly tuned Java compiler specifically for the Java editor i.e., parsing and lexing for features such as syntax coloring, code completion.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package com.sun.source.util;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;

import com.sun.source.tree.*;

/**
 * A path of tree nodes, typically used to represent the sequence of ancestor
 * nodes of a tree node up to the top-level {@code CompilationUnitTree} node.
 *
 * @author Jonathan Gibbons
 * @since 1.6
 */
public class TreePath implements Iterable {
    /**
     * Returns a tree path for a tree node within a compilation unit,
     * or {@code null} if the node is not found.
     * @param unit the compilation unit to search
     * @param target the node to locate
     * @return the tree path
     */
    public static TreePath getPath(CompilationUnitTree unit, Tree target) {
        return getPath(new TreePath(unit), target);
    }

    /**
     * Returns a tree path for a tree node within a subtree identified by a TreePath object.
     * Returns {@code null} if the node is not found.
     * @param path the path in which to search
     * @param target the node to locate
     * @return the tree path of the target node
     */
    public static TreePath getPath(TreePath path, Tree target) {
        Objects.requireNonNull(path);
        Objects.requireNonNull(target);

        class Result extends Error {
            static final long serialVersionUID = -5942088234594905625L;
            TreePath path;
            Result(TreePath path) {
                this.path = path;
            }
        }

        class PathFinder extends TreePathScanner {
            public TreePath scan(Tree tree, Tree target) {
                if (tree == target) {
                    throw new Result(new TreePath(getCurrentPath(), target));
                }
                return super.scan(tree, target);
            }
        }

        if (path.getLeaf() == target) {
            return path;
        }

        try {
            new PathFinder().scan(path, target);
        } catch (Result result) {
            return result.path;
        }
        return null;
    }

    /**
     * Creates a TreePath for a root node.
     * @param node the root node
     */
    public TreePath(CompilationUnitTree node) {
        this(null, node);
    }

    /**
     * Creates a TreePath for a child node.
     * @param path the parent path
     * @param tree the child node
     */
    public TreePath(TreePath path, Tree tree) {
        if (tree.getKind() == Tree.Kind.COMPILATION_UNIT) {
            compilationUnit = (CompilationUnitTree) tree;
            parent = null;
        }
        else {
            compilationUnit = path.compilationUnit;
            parent = path;
        }
        leaf = tree;
    }
    /**
     * Returns the compilation unit associated with this path.
     * @return the compilation unit
     */
    public CompilationUnitTree getCompilationUnit() {
        return compilationUnit;
    }

    /**
     * Returns the leaf node for this path.
     * @return the leaf node
     */
    public Tree getLeaf() {
        return leaf;
    }

    /**
     * Returns the path for the enclosing node, or {@code null} if there is no enclosing node.
     * @return the path for the enclosing node
     */
    public TreePath getParentPath() {
        return parent;
    }

    /**
     * Iterates from leaves to root.
     */
    @Override
    public Iterator iterator() {
        return new Iterator() {
            @Override
            public boolean hasNext() {
                return next != null;
            }

            @Override
            public Tree next() {
                if (next == null) {
                    throw new NoSuchElementException();
                }
                Tree t = next.leaf;
                next = next.parent;
                return t;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }

            private TreePath next = TreePath.this;
        };
    }

    private CompilationUnitTree compilationUnit;
    private Tree leaf;
    private TreePath parent;
}