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Java: Repaint in Swing Not Working

I am learning java swing and am having trouble with the following program. It creates a small frame with a quit button at top. The objective is to display coordinates wherever the mouse is clicked. When I click the mouse 2 unwanted things are happening:
the quit button is overridden by the mouse clicks and it no longer responds (instead of responding to event and quitting, it displays coordinates on top of the quit button).
when I click at a new location, the coordinates from the old location persist.
I used removeAll() and revalidate() before doing repaint() based on this discussion but that has not helped. This code is taken from here and the code to says to research online documentation for why this is happening.
Any pointers?
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.BorderLayout;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JLabel;
public class QuitCoordinateTest {
public static void main(String[] args){
GUI gui = new GUI();
}
}
class MyFrame extends JFrame implements ActionListener{
int clickX;
int clickY;
public void paint(Graphics g){
g.drawString("" + clickX + ", " + clickY, clickX, clickY);
}
public void actionPerformed(ActionEvent e){
System.exit(0);
}
}
//=======================================================//
class GUI extends MyFrame {
JButton quitButton = new JButton("Quit");
public GUI(){
MyFrame displayWindow = new MyFrame();
displayWindow.setTitle("Title");
/*
JPanel buttonPanel = new JPanel();
buttonPanel.add(quitButton);
displayWindow.getContentPane().add(buttonPanel,BorderLayout.NORTH);
JPanel textPanel = new JPanel();
*/
displayWindow.getContentPane().add(quitButton,BorderLayout.NORTH);
quitButton.addActionListener(displayWindow);
displayWindow.setSize(201,201);
displayWindow.setVisible(true);
// displayWindow.pack();
displayWindow.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
displayWindow.addMouseListener(new MouseProc(displayWindow));
}//end constructor
}//end class GUI definition
//=======================================================//
//This listener class monitors for mouse presses and
// displays the coordinates of the mouse pointer when the
// mouse is pressed on the source object.
class MouseProc extends MouseAdapter{
MyFrame refToWin;
MouseProc(MyFrame inWin){
refToWin = inWin;
}
//Override the mousePressed method to determine and
// display the coordinates when the mouse is pressed.
public void mousePressed(MouseEvent e){
refToWin.removeAll();
refToWin.clickX = e.getX();
refToWin.clickY = e.getY();
//Force the JFrame object to be repainted in order to
// display the coordinate information.
refToWin.removeAll();
refToWin.validate();
refToWin.repaint();
}
}

repaint() is working fine.
Avoid drawing directly on the JFrame.
Instead draw in the protected void paintComponent(Graphics g) method override of a JPanel that is then displayed in your JFrame.
Be sure to call the super's paintComponent(g) method inside of your paintComponent override -- this will erase the old images and is the reason for one of your problems.
Use reasonable comments in your code. Too many comments and too much text distracts and makes understanding your code harder, not easier.
Calling removeAll() on your JFrame will do just that -- remove all components including your button. Why are you calling this? Are you sure that you want to call this method?
A minor nitpick -- you'll want to avoid directly setting the fields of another class, such as your clickX and clickY fields. Instead, make them private, and only allow outside classes to modify them through public methods. While it may not matter much for this small program, it will matter greatly when you start scaling up your programming and create large programs with complex interactions. The key to success here will be to limit and control all communication between classes to avoid hard to detect side effects.
For example, something like...
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
String str = String.format("[%d, %d]", clickX, clickY);
g.drawString(str, clickX, clickY);
}
public int getClickX() {
return clickX;
}
public void setClickX(int clickX) {
this.clickX = clickX;
}
public int getClickY() {
return clickY;
}
public void setClickY(int clickY) {
this.clickY = clickY;
}
For example
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class DetectClicks extends JPanel {
private static final int PREF_W = 800;
private static final int PREF_H = 650;
private int clickX;
private int clickY;
public DetectClicks() {
MyMouseListener mouseAdapter = new MyMouseListener(this);
addMouseListener(mouseAdapter);
addMouseMotionListener(mouseAdapter); // to allow dragging!
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
String str = String.format("[%d, %d]", clickX, clickY);
g.drawString(str, clickX, clickY);
}
public int getClickX() {
return clickX;
}
public void setClickX(int clickX) {
this.clickX = clickX;
}
public int getClickY() {
return clickY;
}
public void setClickY(int clickY) {
this.clickY = clickY;
}
private static void createAndShowGui() {
DetectClicks mainPanel = new DetectClicks();
JFrame frame = new JFrame("DetectClicks");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class MyMouseListener extends MouseAdapter {
private DetectClicks detectClicks;
public MyMouseListener(DetectClicks detectClicks) {
this.detectClicks = detectClicks;
}
#Override
public void mousePressed(MouseEvent evt) {
showPoint(evt);
}
#Override
public void mouseDragged(MouseEvent evt) {
showPoint(evt);
}
private void showPoint(MouseEvent evt) {
detectClicks.setClickX(evt.getX());
detectClicks.setClickY(evt.getY());
detectClicks.repaint();
}
}

Your event is getting consumed by the handler that prints the coordinates, you need to redispatch the event so that the button can see it. You can do it like this, inside the coordinate display event handler:
Component c = e.getComponent();
c.getParent().dispatchEvent( e );
Also, I'd be tempted to use the glass pane of the frame, and put a JLabel on it with the co-ordinates rather than messing with the paint method.

you don't have to use any of repaint(),invalidate() etc.
i highly recommend to use
SwingUtilities.invokeLater(new Runnable() {
public void run() {
//TODO udpdate UI compontents, layouts etc.
}
});
this guarantees that UI components update on real time. Because we don't know when the system update UI hierarchy so we can't force it. This allow system to determine by it's self.

Creating a java method that can continuously update variables

I've been taking AP Computer Science this year as a sophomore in high school and we mainly cover material like loops, classes, methods, general CS logic, and some math stuff. I am missing what I really loved about coding in the first place, making games. Now every game I have made had some sort of way to manage it whether it was using timers in visual basic or a XNA plugin for c# that setup a update method for me. The problem is I have not learned how to do this for java in my course. I've read up a little on threads and implements runnable but i'm not really sure where I'm going with it.
Class 1
import java.awt.FlowLayout;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class GFXScreen extends JFrame
{
/**
* #param screenHeigth
* #param screenHeigth
* #param The file name of the image. Make sure to include the extension type also
* #param The title at the top of the running screen
* #param The height of the screen
* #param The width of the screen
*/
public GFXScreen(String fileName, String screenTitle, int screenHeight, int screenWidth)
{
setLayout(new FlowLayout());
image1 = new ImageIcon(getClass().getResource(fileName));
label1 = new JLabel(image1);
this.add(label1);
//Set up JFrame
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.setVisible(true);
this.setTitle(screenTitle);
this.setSize(screenWidth, screenHeight);
}
/**
* #param desired amount to move picture
*/
public void updatePic(int increment)
{
//update pos
label1.setBounds(label1.bounds().x, label1.bounds().y - increment,
label1.bounds().width, label1.bounds().height);
}
private ImageIcon image1;
private JLabel label1;
}
Class 2
public class MainClass implements Runnable {
public static void main(String[] args)
{
(new Thread(new MainClass())).start();
GFXScreen gfx = new GFXScreen("pixel_man.png", "pixel_Man", 1000, 1000);
}
public void run()
{
gfx.updatePic(1);
}
}
In this instance what I want to happen is, I want a picture that starts in the top to slowly move down smoothly to the bottom. How would i do this?

Suggestions:
Again, a Swing Timer works well for simple Swing animations or simple game loops. It may not be the greatest choice for complex or rigorous tame loops as its timing is not precise.
Most game loops will not be absolutely precise with time slices
And so your game model should take this into consideration and should note absolute time slices and use that information in its physics engine or animation.
If you must use background threading, do take care that most all Swing calls are made on the Swing event thread. To do otherwise will invite pernicious infrequent and difficult to debug program-ending exceptions. For more details on this, please read Concurrency in Swing.
I avoid using null layouts, except when animating components, as this will allow my animation engine to place the component absolutely.
When posting code here for us to test, it's best to avoid code that uses local images. Either have the code use an image easily available to all as a URL or create your own image in your code (see below for a simple example).
Your compiler should be complaining to you about your using deprecated methods, such as bounds(...), and more importantly, you should heed those complaints as they're there for a reason and suggest increased risk and danger if you use them. So don't use those methods, but instead check the Java API for better substitutes.
Just my own personal pet peeve -- please indicate that you've at least read our comments. No one likes putting effort and consideration into trying to help, only to be ignored. I almost didn't post this answer because of this.
For example:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.AbstractAction;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
#SuppressWarnings("serial")
public class GfxPanel extends JPanel {
private static final int BI_WIDTH = 26;
private static final int BI_HEIGHT = BI_WIDTH;
private static final int GAP = 6;
private static final Point INITIAL_LOCATION = new Point(0, 0);
private static final int TIMER_DELAY = 40;
public static final int STEP = 1;
private ImageIcon image1;
private JLabel label1;
private Point labelLocation = INITIAL_LOCATION;
private int prefW;
private int prefH;
private Timer timer;
public GfxPanel(int width, int height) {
// the only time I use null layouts is for component animation.
setLayout(null);
this.prefW = width;
this.prefH = height;
// My program creates its image so you can run it without an image file
image1 = new ImageIcon(createMyImage());
label1 = new JLabel(image1);
label1.setSize(label1.getPreferredSize());
label1.setLocation(labelLocation);
this.add(label1);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(prefW, prefH);
}
public void startAnimation() {
if (timer != null && timer.isRunning()) {
timer.stop();
}
labelLocation = INITIAL_LOCATION;
timer = new Timer(TIMER_DELAY, new TimerListener());
timer.start();
}
// My program creates its image so you can run it without an image file
private Image createMyImage() {
BufferedImage bi = new BufferedImage(BI_WIDTH, BI_HEIGHT,
BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = bi.createGraphics();
g2.setColor(Color.red);
g2.fillRect(0, 0, BI_WIDTH, BI_HEIGHT);
g2.setColor(Color.blue);
int x = GAP;
int y = x;
int width = BI_WIDTH - 2 * GAP;
int height = BI_HEIGHT - 2 * GAP;
g2.fillRect(x, y, width, height);
g2.dispose();
return bi;
}
private class TimerListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
int x = labelLocation.x + STEP;
int y = labelLocation.y + STEP;
labelLocation = new Point(x, y);
label1.setLocation(labelLocation);
repaint();
if (x + BI_WIDTH > getWidth() || y + BI_HEIGHT > getHeight()) {
System.out.println("Stopping Timer");
((Timer) e.getSource()).stop();
}
}
}
private static void createAndShowGui() {
final GfxPanel gfxPanel = new GfxPanel(900, 750);
JButton button = new JButton(new AbstractAction("Animate") {
#Override
public void actionPerformed(ActionEvent arg0) {
gfxPanel.startAnimation();
}
});
JPanel buttonPanel = new JPanel();
buttonPanel.add(button);
JFrame frame = new JFrame("GFXScreen");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(gfxPanel);
frame.getContentPane().add(buttonPanel, BorderLayout.PAGE_END);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

What I always use is an infinite loop that calls an update method each iteration, in that method, you would do whatever was required to update the state of the game or render a GUI.
Example
public static void main(String[] args){
// Initialise game
while(true){
updateGame();
}
}
public static void updateGame(){
// Update things here.
}
What I also do ,which is a little more complex, is create and interface called IUpdateListener and have certain classes that are specialised for a certain element of the game. I would example have an InputListener, an AIListener, each handling a certain element of game updating.
public interface IUpdateListener{
public void update();
}
public class Main{
public static ArrayList<IUpdateListener> listeners = new ArrayList<IUpdateListener>();
public static void main(String[] args){
listeners.add(new InputListener());
while(true){
for(IUpdateListener listener : listeners){
listener.update();
}
}
}
}
public class InputListener implements IUpdateListener{
public void update(){
// Handle user input here etc
}
}

Why does a fireContentsChanged call of a JList freezes the entire GUI?

I had some problems with freezing SWING GUIs when re-rendering a JTable with a custom cell renderer in Java. So I asked the question "Why does a JTable view update block the entire GUI?". The answers pointed to the fact, that a JList without modifying JTable and overwriting doLayout might be a better choice. So I implemented the example with a JList and ran into the same problem: while generating data, everything works fine and the progress bar moves. But when the view is updated, the program freezes and the progress bar stops moving.
Please note, that the sleep statement is there only to let the generation take a longer, more realistic time (reading thousands of data sets via JDBC and create objects out of them takes a lot time). One could remove it and increment the number of generated items. But you can clearly see, that the HTML rendering is quite slow. But I need this colors and the two lines (if not necessarily so many different colors).
So could you please tell me, where my mistake is? I think, that EDT and other work is separated through separate threads and I cannot see any mistke.
Update: I looked around at SO and found this question "https://stackoverflow.com/a/20813122/2429611". There is said:
The more interesting question would be how to avoid that UI blocking, but I don't think that's possible with just Swing, you'll have to implement some lazy loading, or rendering in batches.
This would mean, that I cannot solve my problem. Is this correct?
package example;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.AbstractListModel;
import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.ListCellRenderer;
import javax.swing.SwingUtilities;
public class ListExample extends AbstractListModel {
static List<DemoObject> internalList = new ArrayList<>();
#Override
public int getSize() {
return internalList.size();
}
#Override
public DemoObject getElementAt(int index) {
return internalList.get(index);
}
public void fireContentsChanged() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
fireContentsChanged(this, 0, -1);
}
});
}
static class MyCellRenderer extends JLabel implements ListCellRenderer<ListExample.DemoObject> {
public MyCellRenderer() {
setOpaque(true);
}
#Override
public Component getListCellRendererComponent(JList<? extends ListExample.DemoObject> list,
ListExample.DemoObject value,
int index,
boolean isSelected,
boolean cellHasFocus) {
setText("<html>" + value.toString()
+ "<br/>"
+ "<span bgcolor=\"#ff0000\">Line 2; Color = " + value.c + "</span>");
Color background;
Color foreground;
// check if this cell represents the current DnD drop location
JList.DropLocation dropLocation = list.getDropLocation();
if (dropLocation != null
&& !dropLocation.isInsert()
&& dropLocation.getIndex() == index) {
background = Color.BLUE;
foreground = Color.WHITE;
// check if this cell is selected
} else if (isSelected) {
background = Color.RED;
foreground = Color.WHITE;
// unselected, and not the DnD drop location
} else {
background = value.c; //Color.WHITE;
foreground = Color.BLACK;
};
setBackground(background);
setForeground(foreground);
return this;
}
}
static class DemoObject {
String str;
Color c;
public DemoObject(String str, int color) {
this.str = str;
this.c = new Color(color);
}
#Override
public String toString() {
return str;
}
}
static JPanel overlay;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("Example");
frame.setLayout(new BorderLayout(4, 4));
// Add JTable
final ListExample model = new ListExample();
JList list = new JList(model);
list.setCellRenderer(new MyCellRenderer());
frame.add(new JScrollPane(list), BorderLayout.CENTER);
// Add button
Box hBox = Box.createHorizontalBox();
hBox.add(new JButton(new AbstractAction("Load data") {
#Override
public void actionPerformed(ActionEvent e) {
new Thread(new Runnable() {
#Override
public void run() {
overlay.setVisible(true);
internalList.clear();
System.out.println("Generating data ...");
SecureRandom sr = new SecureRandom();
for (int i = 0; i < 10000; i++) {
internalList.add(
new DemoObject(
"String: " + i + " (" + sr.nextFloat() + ")",
sr.nextInt(0xffffff)
)
);
// To create the illusion, that data are
// fetched via JDBC (which takes a little
// while), this sleep statement is embedded
// here. In a real world scenario, this wait
// time is caused by talking to the database
// via network
if (i%10 == 0) {
try {
Thread.sleep(1);
} catch (Exception e) {
}
}
}
System.out.println("Updating view ...");
model.fireContentsChanged();
overlay.setVisible(false);
System.out.println("Finished.");
}
}).start();
}
}));
hBox.add(Box.createHorizontalGlue());
frame.add(hBox, BorderLayout.NORTH);
// Create loading overlay
overlay = new JPanel(new FlowLayout(FlowLayout.CENTER)) {
#Override
protected void paintComponent(Graphics g) {
g.setColor(new Color(0, 0, 0, 125));
g.fillRect(0, 0, getWidth(), getHeight());
super.paintComponent(g);
}
};
overlay.setOpaque(false);
overlay.setBackground(new Color(0, 0, 0, 125));
JProgressBar bar = new JProgressBar();
bar.setIndeterminate(true);
overlay.add(bar);
frame.setGlassPane(overlay);
frame.getGlassPane().setVisible(false);
// Create frame
frame.setSize(600, 400);
frame.setVisible(true);
}
});
}
}

there are three problems (recreating, reseting the model, and custom Renderer stoped to works)
JList (JComboBox hasn't) has an issue by removing more than 999 items, you have to set a new model to JList
see important for ComboBoxModel extends AbstractListModel implements MutableComboBoxModel for setElementAt(to hold current selection)
usage of public void fireContentsChanged() { is wrong, don't see reason to use this way, again is about to replace current, reset the model
. e.g. with success atr runtime and by recrusive testing for/if event (fired)
setModel(new DefaultListModel(list.toArray()) {
protected void fireContentsChanged(Object obj, int i, int j) {
if (!isFired)
super.fireContentsChanged(obj, i, j);
}
});

Manual Positioning of Image in JFrame

I am trying to create a JFrame that displays an image from a file path onto a particular position on the JFrame. At a later time (when a button is clicked), I want the image to move positions, say, 50 pixles to the left. If a layout manager is necessary, I want to use the null layout, as this is a project for myself and I am not quite ready to learn how to write my own layout manager.
So far, I have managed to display a BufferedImage in a frame, but I do not know how to specify its position.
Is using a BufferedImage even the correct approach? What is the best way to go about doing this?
Update: I tried to follow your suggestion of using mouselistener and it resulted in this:
class ImgComponent extends JComponent implements ChangeListener, MouseListener {
MovableImage mi;
public ImgComponent(MovableImage mi) {
this.mi = mi;
mi.addListener(this);
mi.addListener1(this);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(mi.i, mi.getX(), mi.getY(), null);
}
#Override
public void stateChanged(ChangeEvent e) {
repaint();
}
#Override
public void mouseClicked(MouseEvent e) {
mi.setPos(100, 100);
System.out.println("yay");
}
}
But unfortinely, the mouseClicked event never triggers. I just want that damn image to move, lol.

Here's a complete example that uses the model/view/controller pattern. (Just dump all snippets after each other in a single .java file.)
import java.awt.*;
import java.awt.event.ActionEvent;
import java.util.*;
import java.util.List;
import javax.swing.*;
import javax.swing.event.*;
// A class encapsulating an image and a x-coordinate (a "model")
class MovableImage {
Image i = new ImageIcon("duke.png").getImage();
private int x = 0;
// Observers that are interested in movements.
List<ChangeListener> listeners = new ArrayList<ChangeListener>();
public void addListener(ChangeListener cl) {
listeners.add(cl);
}
public int getX() {
return x;
}
public void incrementX() {
x += 10;
// Notify those interested.
for (ChangeListener cl : listeners)
cl.stateChanged(null);
}
}
// A graphical component displaying the model.
// Object of this class are interested in movement because when the image moves,
// this component needs to be repainted.
class ImgComponent extends JComponent implements ChangeListener {
// The movable image to present.
MovableImage mi;
public ImgComponent(MovableImage mi) {
this.mi = mi;
mi.addListener(this);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(mi.i, mi.getX(), 10, null);
}
// This method is called from MovableImage when the position changes.
#Override
public void stateChanged(ChangeEvent e) {
repaint();
}
}
// Main class.
public class FrameTestBase extends JFrame {
public static void main(String args[]) {
// Create the "model".
final MovableImage mi = new MovableImage();
FrameTestBase t = new FrameTestBase();
t.setLayout(new BorderLayout());
// Add a component presenting the model.
t.add(new ImgComponent(mi), BorderLayout.CENTER);
// Create a button which increments x when clicked on.
t.add(new JButton(new AbstractAction("Move right") {
#Override
public void actionPerformed(ActionEvent e) {
mi.incrementX();
}
}), BorderLayout.SOUTH);
// Show it.
t.setDefaultCloseOperation(EXIT_ON_CLOSE);
t.setSize(400, 400);
t.setVisible(true);
}
}
Regarding your edit:
You need to add the mouse listener as well. In the constructor:
public ImgComponent(MovableImage mi) {
this.mi = mi;
mi.addListener(this);
mi.addListener1(this);
}
add the following line at the bottom:
addMouseListener(this);

Where can I put mouse event handling code so that it is out of the way but can still manipulate objects?

I'm learning Java here and trying to get to grips with classes and how best to catch mouse events etc. for my little game, so please be patient and give my some hints.
The main class of my project extends JFrame and upon construction adds to itself an object of a class which extends JPanel. This JPanel covers the whole window and it is this I am using to paint stuff to the screen. Then I have a class called Scene which extends nothing but which stores all the references to the current objects on the screen and is responsible for compiling them all and passing them back to the JPanel. I didn't want to put the full mouse event code in the JPanel because it would be so messy so I though I'd create another class for that called MEs and let each scene have one. My thinking was, this way each mes object can access the objects in each scene easily. So my code is looking like this:
class DPanel extends JPanel {
Scene scCurrent;
public DPanel() {
scCurrent = new Scene();
addMouseMotionListener(new MouseAdapter() {
public void mouseMoved(MouseEvent me) { scCurrent.mes.moved(me); }
});
...
}
...
but of course, inside scCurrent.mes.moved() I don't even know how to change the cursor. It doesn't recognise setCursor() in there. How can I change the cursor and access objects that are higher up the tree like I'd need to to switch scene? Or is there some other place I can tuck my mouse event handling code that will not bumph-out out my JPanel?

You are trying to separate out the control code from the view (GUI) code, and this is a good thing. A solution is to give the view code public methods that allow outside code to change its state, and give the control classes a reference to the view so that the controls (i.e., MouseListeners, MouseMotionListeners, ActionListeneres) can call these methods on a proper reference and change the view's states.
Edit 1
It may be easier just to show you an example:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
public class ViewControl {
private static void createAndShowGui() {
View view = new View();
Control control = new Control(view);
view.addMouseAdapter(control);
JFrame frame = new JFrame("ViewControl");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(view);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
#SuppressWarnings("serial")
class View extends JPanel {
private static final int PREF_W = 400;
private static final int PREF_H = PREF_W;
private List<Point> points = new ArrayList<Point>();
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (points.size() > 1) {
for (int i = 0; i < points.size() - 1; i++) {
int x1 = points.get(i).x;
int y1 = points.get(i).y;
int x2 = points.get(i + 1).x;
int y2 = points.get(i + 1).y;
g.drawLine(x1, y1, x2, y2);
}
}
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
public void addMouseAdapter(MouseAdapter adapter) {
// addMouseListener(adapter);
addMouseMotionListener(adapter);
}
public void addPoint(Point p) {
points.add(p);
repaint();
}
}
class Control extends MouseAdapter {
private View view;
public Control(View view) {
this.view = view;
}
#Override
public void mouseDragged(MouseEvent e) {
view.addPoint(e.getPoint());
}
}