1. Swing Graphics ● Empty Swing containers have no visual appearance except for a background color ● Every JComponent must have a paintComponent method that is called when the component is first made visible or needs to be redrawn for some reason ● The JPanel component is a lightweight container, making it suitable as a drawing area ● A common way to do graphics is to extend the JPanel class and override the paintComponent method

2. The paintComponent Method ● Called by the JVM when this component needs to be redrawn ● A single argument, the component's graphics context (class: Graphics ), is passed when paintComponent is called ● A Graphics object contains: – the component on which it draws – the current color and font – location origin – clipping information – and more

3. Graphics vs. Graphics2D ● The Graphics class has limitations: – Cannot use real number coordinates – Cannot draw dotted, dashed, or variable-width lines – Cannot easily draw complex curves or fill complex shapes – Cannot use textures or gradient colors to fill shapes ● The newer Graphics2D class extends Graphics and provides these capabilities ● All GUI components use a Graphics2D object but paintComponent passes a Graphics object for backward compatibility

4. General Approach public class MyPanel extends JPanel { // instance variables public MyPanel() { // public constructor } // public methods // private helper methods public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D)g; // drawing messages sent to g2d... }

5. The paintComponent Method ● super.paintComponent(g) is called first to ensure that painting responsibilities defined in JPanel are carried out ● You should not call paintComponent directly; it is called by the JVM when it needs to ● You can indirectly call paintComponent on a component by using component.repaint()

6. Some Basic Graphics Methods ● void setColor(Color color) ● void setFont(Font font) ● void drawString(String text, int x, int y) – (x,y) is the coordinate of the lower left corner of the drawn string's leftmost character

7. Graphics Example import javax.swing.*; import java.awt.*; public class GraphicsPanel extends JPanel { public GraphicsPanel() { setPreferredSize(new Dimension(200,200)); setBackground(Color.magenta); // panel color } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; g2D.setColor(Color.blue); // drawing color g2D.setFont(new Font("Helvetica", Font.BOLD, 24)); g2D.drawString("Hello World", 25, 25); }

8. Graphics Example (cont'd) import javax.swing.*; import java.awt.*; import java.awt.event.*; public class MainFrame extends JFrame { public MainFrame() { setSize(new Dimension(500,300)); setLocation(100,100); addWindowListener(new WindowAdapter () { public void windowClosing(WindowEvent e) { dispose(); System.exit(0); } }); getContentPane().setLayout( new FlowLayout(FlowLayout.CENTER)); GraphicsPanel gp = new GraphicsPanel(); getContentPane().add(gp); setVisible(true); } public static void main(String[] args) { new MainFrame(); }

9. Display

10. Notes On The Example ● GraphicsPanel extends JPanel so that the paintComponent method can be overridden ● If you forget to call super 's paintComponent method, you can get pixels from another desktop frame as background garbage ● The background color is associated with the panel; the paint color with the Graphics2D object ● The MainFrame class extends JFrame and an instance of it is created in the main method

11. Drawing Shapes ● You can draw any object that implements the java.awt.Shape interface. ● Example: suppose g2D is a Graphics2D object: Shape s =...; g2D.draw(s); The Java library supplies a number of classes that implement the Shape interface type.

12. Inheritance Hierarchy of Geometric Shape Classes

13. Line Shapes ● java.awt.geom.Line2D is an abstract class with two concrete subclasses that are also inner classes: – Line2D.Double – Line2D.Float ● A Line2D object represents a line segment in (x,y) coordinate space. ● To create a line segment, first create its endpoints using the java.awt.geom.Point2D class

14. Line Example import java.awt.geom.*;... public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Point2D.Double corner1 = new Point2D.Double(100, 50); Point2D.Double corner2 = new Point2D.Double(50, 150); Point2D.Double corner3 = new Point2D.Double(150, 150); Line2D.Double side1 = new Line2D.Double(corner1, corner2); Line2D.Double side2 = new Line2D.Double(corner2, corner3); Line2D.Double side3 = new Line2D.Double(corner3, corner1); g2D.draw(side1); g2D.draw(side2); g2D.draw(side3); }...

15. An Easier Way: Polygons import java.awt.*;... public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Polygon triangle = new Polygon(new int[] {100, 50, 150}, new int[] {50, 150, 150}, 3); g2D.draw(triangle); // produces same triangls as before }... Polygon(int[] xpoints, int[] ypoints, int npoints) java.awt.Polygon implements the Shape interface. Specify the x and y coordinates of a closed polygon's vertices with the following constructor:

16. Rectangular Shapes ● Abstract subclasses of RectangularShape : – Rectangle2D, RoundRectangle2D – Ellipse2D, Arc2D ● Each has concrete.Double and.Float subclasses ● Each constructor requires x,y coordinate of upper left corner of bounding rectangle, and also the rectangle's width and height ● Use draw to draw an outline of the shape in the current color. ● Use fill to fill the shape with the current color.

17. Additional Parameters for Rounded Rectangles arcWidth arcHeight (x,y) height width

18. Example public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Rectangle2D.Double rect1 = new Rectangle2D.Double(25,25,100,100); g2D.setColor(Color.black); g2D.draw(rect1); RoundRectangle2D.Double rect2 = new RoundRectangle2D.Double(50,50,100,100,80,30); g2D.setColor(Color.green); g2D.fill(rect2); Ellipse2D.Double rect3 = new Ellipse2D.Double(75,75,100,80); g2D.setColor(Color.blue); g2D.fill(rect3); }

19. New Display

20. Additional Parameters for Arcs (x,y) 0 -270 90 ±180 270 -90 width height startAngleangularExtent Closure type for the arc: OPEN, CHORD, or PIE

21. Arc Example public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Arc2D.Double arc = new Arc2D.Double(25,25,150,100,0,120,Arc2D.PIE); g2D.setColor(Color.black); g2D.fill(arc); arc = new Arc2D.Double(25,25,150,100,120,120,Arc2D.PIE); g2D.setColor(Color.green); g2D.fill(arc); arc = new Arc2D.Double(25,25,150,100,240,120,Arc2D.PIE); g2D.setColor(Color.orange); g2D.fill(arc); }

22. Arc Display

23. Arc Example Modified public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Arc2D.Double arc = new Arc2D.Double(25,25,150,100,0,120,Arc2D.CHORD); g2D.setColor(Color.black); g2D.fill(arc); arc = new Arc2D.Double(25,25,150,100,120,120,Arc2D.CHORD); g2D.setColor(Color.green); g2D.fill(arc); arc = new Arc2D.Double(25,25,150,100,240,120,Arc2D.CHORD); g2D.setColor(Color.orange); g2D.fill(arc); }

24. New Arc Display

25. More Features ● Other things you can do with Shape s: – Check for containment of points and rectangles – Get bounding rectangle – Check for intersection with another bounding rectangle ● Other things you can do with 2D graphics contexts: – Change stroke properties – Draw images – Perform rotations, scalings, and translations