LayerTest.java

import javafx.application.Application;
import javafx.scene.Group;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.scene.control.ChoiceBox;
import javafx.collections.FXCollections;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;

public class LayerTest extends Application {
    
    private Group root;
    private BorderPane borderPane;
    private Canvas layer1;
    private Canvas layer2;
    private GraphicsContext gc1;
    private GraphicsContext gc2;
    private ChoiceBox cb;
    
    private void createLayers(){
        
        // Layers 1&2 are the same size
        layer1 = new Canvas(300,250);
        layer2 = new Canvas(300,250);
        
        // Obtain Graphics Contexts
        gc1 = layer1.getGraphicsContext2D();
        gc1.setFill(Color.GREEN);
        gc1.fillOval(50,50,20,20);
        gc2 = layer2.getGraphicsContext2D();
        gc2.setFill(Color.BLUE);
        gc2.fillOval(100,100,20,20);
    }
    
    private void handleLayers(){
        // Handler for Layer 1
        layer1.addEventHandler(MouseEvent.MOUSE_PRESSED, new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent e) {          
                gc1.fillOval(e.getX(),e.getY(),20,20);
            }
        });
        
         // Handler for Layer 2
        layer2.addEventHandler(MouseEvent.MOUSE_PRESSED, new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent e) {
                gc2.fillOval(e.getX(),e.getY(),20,20);
            }
        });
    }
    
    private void createChoiceBox(){
        cb = new ChoiceBox();
        cb.setItems(FXCollections.observableArrayList("Layer 1 is GREEN", "Layer 2 is BLUE"));
        cb.getSelectionModel().selectedItemProperty().addListener(new ChangeListener(){
            @Override
            public void changed(ObservableValue o, Object o1, Object o2){
                if(o2.toString().equals("Layer 1 is GREEN")){
                    layer1.toFront();
                }else if(o2.toString().equals("Layer 2 is BLUE")){
                    layer2.toFront();
                }
            }
        });  
        cb.setValue("Layer 1 is GREEN");
    }
    
    private void addLayers(){
        // Add Layers
        borderPane.setTop(cb);        
        Pane pane = new Pane();
        pane.getChildren().add(layer1);
        pane.getChildren().add(layer2);
        layer1.toFront();
        borderPane.setCenter(pane);    
        root.getChildren().add(borderPane);
    }
    
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        
        // Build GUI
        borderPane = new BorderPane();  
        primaryStage.setTitle("Layer Test");
        root = new Group();
        createLayers();
        handleLayers();
        createChoiceBox();
        addLayers();  
      
        // Show Scene
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }
}