путь к файлу элемента дерева javafx

у меня есть вопрос для этого примера кода.

import java.io.File;
import java.io.IOException;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.BasicFileAttributes;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class CopyOfTreeViewSample extends Application {
    public static Image folderCollapseImage=new Image(ClassLoader.getSystemResourceAsStream("treeviewsample/folder.png"));
    public static Image folderExpandImage=new Image(ClassLoader.getSystemResourceAsStream("treeviewsample/folder-open.png"));
    public static Image fileImage=new Image(ClassLoader.getSystemResourceAsStream("treeviewsample/text-x-generic.png"));
    public static Image rootImage = new Image(ClassLoader.getSystemResourceAsStream("treeviewsample/computer.png"));
    private TreeView treeView;
      public static void main(String[] args) {
            launch(args);
      }
  @Override
  public void start(Stage stage) {
    Scene scene = new Scene(new Group());
    stage.setTitle("Sample");
    stage.setWidth(300);
    stage.setHeight(500);

    VBox vbox = new VBox();
    vbox.setLayoutX(20);
    vbox.setLayoutY(20);

    TreeItem<String> root = new SimpleFileTreeItem(Paths.get("C:\\Users\\Jake"), true);
    treeView = new TreeView<String>(root);

    Button b = new Button("Change");
    b.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent arg0) {
            // TODO Auto-generated method stub
                     ////// How do i this section write code?//////            
     }

    });
    vbox.getChildren().addAll(treeView,b);
    vbox.setSpacing(10);
    ((Group) scene.getRoot()).getChildren().add(vbox);

    stage.setScene(scene);
    stage.show();
  }

  public class SimpleFileTreeItem extends TreeItem<String> {

    private boolean isRoot = false;
    private boolean isFirstTimeChildren = true;
    private boolean isFirstTimeLeaf = true;
    private boolean isLeaf;
    private boolean isDirectory;
    public boolean isDirectory(){return(this.isDirectory);}
    private String fullPath;
    public String getFullPath(){return(this.fullPath);}
    public SimpleFileTreeItem(Path f, Boolean flag) {
        super(f.toString());
        fullPath = f.toString();
        isRoot = flag;
        if(!isRoot)
        {
            if(Files.isDirectory(f))
            {
                isDirectory = true;
                this.setGraphic(new ImageView(folderCollapseImage));
            }
            else
            {
                isDirectory = false;
                this.setGraphic(new ImageView(fileImage));
            }
            //set the value
            if(!fullPath.endsWith(File.separator)){
                String value=f.toString();
                int indexOf=value.lastIndexOf(File.separator);
                if(indexOf>0){
                    this.setValue(value.substring(indexOf+1));
                }else{
                    this.setValue(value);
                }
            }
            this.addEventHandler(TreeItem.branchExpandedEvent(),new EventHandler(){
                @Override
                public void handle(Event e){
                    SimpleFileTreeItem source=(SimpleFileTreeItem)e.getSource();
                    if(source.isDirectory()&&source.isExpanded()){
                        ImageView iv=(ImageView)source.getGraphic();
                        iv.setImage(folderExpandImage);

                    }
                }   
            });

            this.addEventHandler(TreeItem.branchCollapsedEvent(),new EventHandler(){
                @Override
                public void handle(Event e){
                    SimpleFileTreeItem source=(SimpleFileTreeItem)e.getSource();
                    if(source.isDirectory()&&!source.isExpanded()){
                        ImageView iv=(ImageView)source.getGraphic();
                        iv.setImage(folderCollapseImage);
                    }
                }
            });
        }
        else
        {
            this.setExpanded(true);
            if(Files.isDirectory(f))
            {
                isDirectory = true;
                this.setGraphic(new ImageView(rootImage));
            }
            else
            {
                isDirectory = false;
                this.setGraphic(new ImageView(fileImage));
            }
        }   
    }

    @Override
    public ObservableList<TreeItem<String>> getChildren() {
        if (isFirstTimeChildren) {
            isFirstTimeChildren = false;

            /*
             * First getChildren() call, so we actually go off and determine the
             * children of the File contained in this TreeItem.
             */
            super.getChildren().setAll(buildChildren(this));
        }
        return super.getChildren();
    }

    @Override
    public boolean isLeaf() {
        if (isFirstTimeLeaf) {
            isFirstTimeLeaf = false;
            File f = new File(fullPath);
            isLeaf = f.isFile();
        }
        return isLeaf;
    }

    /**
     * Returning a collection of type ObservableList containing TreeItems, which
     * represent all children available in handed TreeItem.
     * 
     * @param TreeItem
     *            the root node from which children a collection of TreeItem
     *            should be created.
     * @return an ObservableList<TreeItem<File>> containing TreeItems, which
     *         represent all children available in handed TreeItem. If the
     *         handed TreeItem is a leaf, an empty list is returned.
     */
    private ObservableList<TreeItem<String>> buildChildren(TreeItem<String> TreeItem) {
        File f = new File(fullPath);
        if (f != null && f.isDirectory()) {
            File[] files = f.listFiles();
            if (files != null) {
                ObservableList<TreeItem<String>> children = FXCollections
                        .observableArrayList();

                for (File childFile : files) {
                    children.add(new SimpleFileTreeItem(childFile.toPath(), false));
                }
                return children;
            }
        }

        return FXCollections.emptyObservableList();
    }   
}

Я хочу выбрать файл, соответствующий пути при нажатии кнопки.

мой путь к проекту eclipse - c:\java\samplecode.

Я пытался решить, используя Absolutepath, результат c:\java\samplecode\samplefile.txt

я хочу этот путь (c:\Users\jake\samplefile.txt)

Спасибо за советы и подсказки.