// Initialize objects used in drawing.

private static final int LINE_MODE = 0;

private static final int RECT_MODE = 1;

private static final int OVAL_MODE = 2;

private boolean isFilled;

private boolean isGradient;

private boolean isDashed;

private Color shapeColor;

private Color gradientColor;

private int shapeMode;

private int lineWidth;

private int dashLength;

private Shape currentShape;

private JLabel statusBar;

private LinkedList<Shape> shapes;

private DynamicStack<Shape> redoStack;

// Constructor instantiates the main interactions within the panel.

public DrawPanel(JLabel statusLabel) {

// Initialize all the required objects for the panel.

statusBar = statusLabel;

isFilled = false;

isGradient = false;

shapeColor = Color.BLACK;

gradientColor = Color.BLACK;

shapeMode = LINE_MODE;

lineWidth = 1;

shapes = new LinkedList<>();

redoStack = new DynamicStack<>();

MouseEventListener drawPanelListener = new MouseEventListener();

// Mouse events.

addMouseListener(drawPanelListener);

addMouseMotionListener(drawPanelListener);

// Initiate color of background.

setBackground(Color.WHITE);

}

// Remove the latest action from drawn shapes, add it to the redo stack.

public void undo() {

Shape shape = shapes.removeLast();

if(shape != null) {

redoStack.push(shape);

}

// Repaint panel after any change.

repaint();

}

// Pop the redo stack, add it to the latest change of shapes if possible.

public void redo() {

Shape shape = redoStack.pop();

if (shape != null) {

shapes.addLast(shape);

}

// Repaint panel after any change.

repaint();

}

// Clear all shapes and redo stack as required.

public void clear() {

shapes.clear();

redoStack.clear();

// Repaint panel after any change.

repaint();

}

// A setter for isFilled.

public void setIsFilled(boolean isFilled) {

this.isFilled = isFilled;

}

// A setter for isGradient.

public void setIsGradient(boolean isGradient) {

this.isGradient = isGradient;

}

// A setter for shapeColor.

public void setShapeColor(Color shapeColor) {

this.shapeColor = shapeColor;

}

// A setter for shapeMode.

public void setShapeMode(int shapeMode) {

this.shapeMode = shapeMode;

}

// A setter for gradientColor.

public void setGradientColor(Color gradientColor) {

this.gradientColor = gradientColor;

}

// A setter for lineWidth.

public void setLineWidth(int lineWidth) {

this.lineWidth = lineWidth;

}

// A setter for isGradient.

public void setIsDashed(boolean isDashed) {

this.isDashed = isDashed;

}

// A setter for dashLength.

public void setDashLength(int dashLength) {

this.dashLength = dashLength;

}

class MouseEventListener extends MouseAdapter {

// Mouse press indicates a new shape drawing has been started

@Override

public void mousePressed(MouseEvent event) {

// Make sure command is from left clicks only to avoid call exceptions.

if (SwingUtilities.isLeftMouseButton(event)) {

// Decide which shape to draw depending on current shape type.

if (shapeMode == LINE_MODE) {

currentShape = new Line(event.getX(), event.getY(), event.getX(), event.getY(), shapeColor, lineWidth, isGradient, gradientColor, isDashed, dashLength);

}

else if (shapeMode == RECT_MODE) {

currentShape = new Rectangle(event.getX(), event.getY(), event.getX(), event.getY(), shapeColor, lineWidth, isGradient, gradientColor, isDashed, dashLength, isFilled);

}

else if (shapeMode == OVAL_MODE) {

currentShape = new Oval(event.getX(), event.getY(), event.getX(), event.getY(), shapeColor, lineWidth, isGradient, gradientColor, isDashed, dashLength, isFilled);

}

// Tell JVM to call paintComponent( g )

repaint();

}

}

// Mouse release indicates the new shape is finished

@Override

public void mouseReleased(MouseEvent event) {

if (SwingUtilities.isRightMouseButton(event)) {

// Cancel current drawing.

currentShape = null;

// Update panel.

repaint();

}

// Make sure command is from left clicks only to avoid call exceptions.

else if (SwingUtilities.isLeftMouseButton(event) && currentShape != null) {

// Update ending coordinates and switch color to current selected color

currentShape.setX2(event.getX());

currentShape.setY2(event.getY());

currentShape.setColor(shapeColor);

// Add the new shape to linked list containing all shapes.

shapes.addLast(currentShape);

// Clear redoStack after new shape is created, redo is now in another branch, discarded.

redoStack.clear();

// Get ready for the next shape to be drawn

currentShape = null;

// Update panel.

repaint();

}

}

// As mouse is dragged, update ending coordinates of currentShape and statusBar

@Override

public void mouseDragged(MouseEvent event) {

if (currentShape != null) {

currentShape.setX2(event.getX());

currentShape.setY2(event.getY());

repaint();

}

statusBar.setText(String.format("(%d, %d)", event.getX(), event.getY()));

}

// As mouse is moved, just update the statusBar

@Override

public void mouseMoved(MouseEvent event) {

statusBar.setText(String.format("(%d, %d)", event.getX(), event.getY()));

}

// handle event when mouse exits JPanel. Clear the status bar.

@Override

public void mouseExited( MouseEvent event ) {

statusBar.setText("(Mouse Outside)");

}

}

// This method is called automatically by the JVM when the window needs to be (re)drawn.

@Override

public void paintComponent(Graphics g) {

super.paintComponent(g);

// Call the draw() method for each shape object in the array

Shape shape = null;

int size = shapes.size();

for (int counter = 0; counter < size; counter++) {

shape = shapes.removeFirst();

shapes.addLast(shape);

shape.draw(g);

}

// If a shape is in progress, draw it on top of all others

if (currentShape != null) {

currentShape.draw(g);

}

}