Edit C:\Program Files\Java\jdk1.8.0_121\com\sun\javafx\scene\traversal\TraversalEngine.java

/*
 * Copyright (c) 2010, 2014, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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 */

package com.sun.javafx.scene.traversal;

import com.sun.javafx.application.PlatformImpl;
import javafx.geometry.BoundingBox;
import javafx.geometry.Bounds;
import javafx.scene.Node;
import javafx.scene.Parent;

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

/**
 * This is abstract class for a traversal engine. There are 2 types : {@link com.sun.javafx.scene.traversal.ParentTraversalEngine}
 * to be used in {@link Parent#setImpl_traversalEngine(ParentTraversalEngine)} to override default behavior
 * and {@link com.sun.javafx.scene.traversal.TopMostTraversalEngine} that is the default traversal engine for scene and subscene.
 *
 * Every engine is basically a wrapper of an algorithm + some specific parent (or scene/subscene), which define engine's root.
 */
public abstract class TraversalEngine{

/**
     * This is the default algorithm for the running platform. It's the algorithm that's used in TopMostTraversalEngine
     */
    static final Algorithm DEFAULT_ALGORITHM = PlatformImpl.isContextual2DNavigation() ? new Hueristic2D() : new ContainerTabOrder();

private final TraversalContext context = new EngineContext(); // This is the context used in calls to this engine's algorithm
    // This is a special context that's used when invoking select "callbacks" to default algorithm in other contexts
    private final TempEngineContext tempEngineContext = new TempEngineContext();
    protected final Algorithm algorithm;

private final Bounds initialBounds =  new BoundingBox(0, 0, 1, 1);
    private final ArrayList<TraverseListener> listeners = new ArrayList<>();

/**
     * Creates engine with the specified algorithm
     * @param algorithm
     */
    protected TraversalEngine(Algorithm algorithm) {
        this.algorithm = algorithm;
    }

/**
     * Creates engine with no algorithm. This makes all the select* calls invalid.
     * @see #canTraverse()
     */
    protected TraversalEngine() {
        this.algorithm = null;
    }

/**
     * Add a listener to traversal engine. The listener is notified whenever focus is changed by traversal inside the associated scene or parent.
     * This can be used with ParentTraversalEngine that has no algorithm to observe changes to the focus inside the parent.
     * @param listener
     */
    public final void addTraverseListener(TraverseListener listener) {
        listeners.add(listener);
    }

/**
     * Fire notifications for listeners. This is called from the TopMostTraversalEngine
     * @param newNode the node which has been focused
     */
    final void notifyTraversedTo(Node newNode) {
        for (TraverseListener l : listeners) {
            l.onTraverse(newNode, getLayoutBounds(newNode, getRoot()));
        }
    }

/**
     * Returns the node that is in the direction {@code dir} starting from the Node {@code from} using the engine's algorithm.
     * Null means there is no Node in that direction
     * @param from the node to start traversal from
     * @param dir the direction of traversal
     * @return the subsequent node in the specified direction or null if none
     * @throws java.lang.NullPointerException if there is no algorithm
     */
    public final Node select(Node from, Direction dir) {
        return algorithm.select(from, dir, context);
    }

/**
     * Returns the first node in this engine's context (scene/parent) using the engine's algorithm.
     * This can be null only if there are no traversable nodes
     * @return The first node or null if none exists
     * @throws java.lang.NullPointerException if there is no algorithm
     */
    public final Node selectFirst() {
        return algorithm.selectFirst(context);
    }

/**
     * Returns the last node in this engine's context (scene/parent) using the engine's algorithm.
     * This can be null only if there are no traversable nodes
     * @return The last node or null if none exists
     * @throws java.lang.NullPointerException if there is no algorithm
     */
    public final Node selectLast() {
        return algorithm.selectLast(context);
    }

/**
     * The root of this engine's context. This is the node that is the root of the tree that is traversed by this engine.
     * @return This engine's root
     */
    protected abstract Parent getRoot();

/**
     * Returns true only if there's specified algorithm for this engine. Otherwise, this engine cannot be used for traversal.
     * The engine might be still useful however, e.g. for listening on traversal changes.
     * @return
     */
    public final boolean canTraverse() {
        return algorithm != null;
    }

/**
     * Gets the appropriate bounds for the given node, transformed into
     * the scene's or the specified node's coordinates.
     * @return bounds of node in {@code forParent} coordinates or scene coordinates if {@code forParent} is null
     */
    private Bounds getLayoutBounds(Node n, Parent forParent) {
        final Bounds bounds;
        if (n != null) {
            if (forParent == null) {
                bounds = n.localToScene(n.getLayoutBounds());
            } else {
                bounds = forParent.sceneToLocal(n.localToScene(n.getLayoutBounds()));
            }
        } else {
            bounds = initialBounds;
        }
        return bounds;
    }

// This is the engine context passed algorithm on select calls
    private final class EngineContext extends BaseEngineContext {
        @Override
        public Parent getRoot() {
            return TraversalEngine.this.getRoot();
        }
    }

// This is the engine context passed to algorithm on select callbacks from other contexts.
    // It can change the root to the node defined in "selectFirstInParent", "selectLastInParent" or
    // "selectInSubtree" methods
    private final class TempEngineContext extends BaseEngineContext {
        private Parent root;

@Override
        public Parent getRoot() {
            return root;
        }

public void setRoot(Parent root) {
            this.root = root;
        }
    }

/**
     * The base class for all engine contexts
     */
    private abstract class BaseEngineContext implements TraversalContext {

/**
         * Returns all traversable nodes in the context's (engine's) root
         */
        @Override
        public List<Node> getAllTargetNodes() {
            final List<Node> targetNodes = new ArrayList<>();
            addFocusableChildrenToList(targetNodes, getRoot());
            return targetNodes;
        }

@Override
        public Bounds getSceneLayoutBounds(Node n) {
            return getLayoutBounds(n, null);
        }

private void addFocusableChildrenToList(List<Node> list, Parent parent) {
            List<Node> parentsNodes = parent.getChildrenUnmodifiable();
            for (Node n : parentsNodes) {
                if (n.isFocusTraversable() && !n.isFocused() && n.impl_isTreeVisible() && !n.isDisabled()) {
                    list.add(n);
                }
                if (n instanceof Parent) {
                    addFocusableChildrenToList(list, (Parent)n);
                }
            }
        }

// All of the methods below are callbacks from traversal context to the default algorithm.
        // They can be used to obtain "default" result for the specified subtree.
        // This is useful when there is some algorithm that overrides behavior for a Parent but parent's children
        // should be again traversed by default algorithm.
        @Override
        public Node selectFirstInParent(Parent parent) {
            tempEngineContext.setRoot(parent);
            return DEFAULT_ALGORITHM.selectFirst(tempEngineContext);
        }

@Override
        public Node selectLastInParent(Parent parent) {
            tempEngineContext.setRoot(parent);
            return DEFAULT_ALGORITHM.selectLast(tempEngineContext);
        }

@Override
        public Node selectInSubtree(Parent subTreeRoot, Node from, Direction dir) {
            tempEngineContext.setRoot(subTreeRoot);
            return DEFAULT_ALGORITHM.select(from, dir, tempEngineContext);
        }
    }
}

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