1. Graphics basic 1

2. 2 Objectives Understand Java coordinate systems. Draw things using the methods in the Graphics class. Override the paintComponent method to draw things. Use a panel as a canvas to draw things. Draw strings, lines, rectangles, ovals, arcs, and polygons. Display image in a GUI component. Using Swing Timers.

3. 3 Java Coordinate System To paint, you need to know where to paint. the origin (0, 0) at the upper-left corner of the component

4. 4 Java Coordinate System Each GUI Component Has its Own Coordinate System

5. 5 The Graphics Class You can draw strings, lines, rectangles, ovals, arcs, polygons, and polylines, using the methods in the Graphics class.

6. 6 The Graphics Class

7. 7 Obtaining Graphics Object The Graphics class is an abstract class that used for displaying figures and images on the screen on different platforms. Whenever a component (e.g., a button, a label, a panel) is displayed, a Graphics object is created for the component.

8. 8 Obtaining Graphics Object You can then apply the methods in the Graphics class to draw things on the label’s graphics context. Think of a GUI component as a piece of paper and the Graphics object as a pencil or paintbrush. You can apply the methods in the Graphics class to draw things on a GUI component.

9. 9 The paintComponent Method To draw you will override paintComponent. –protected void paintComponent(Graphics g). This method, is invoked whenever the component is first displayed or redisplayed. The Graphics object g is created automatically by the JVM for every visible GUI component. The JVM obtains the Graphics object and passes it to invoke paintComponent.

10. 10 Drawing on Panels JPanel can be used to draw graphics (including text) and enable user interaction. To draw in a panel, you create a new class that extends JPanel and override the paintComponent method to tell the panel how to draw things. Invoking super.paintComponent(g) is necessary to ensure that the viewing area is cleared before a new drawing is displayed.

11. 11 Drawing Geometric Figures Drawing Strings Drawing Lines Drawing Rectangles Drawing Ovals Drawing Arcs Drawing Polygons

12. 12 Drawing Strings, Lines drawLine(int x1, int y1, int x2, int y2); drawString(String s, int x, int y);

13. 13 Drawing Rectangles drawRect(int x, int y, int w, int h); fillRect(int x, int y, int w, int h);

14. 14 Drawing Ovals drawOval(int x, int y, int w, int h); fillOval(int x, int y, int w, int h);

15. 15 Drawing Rounded Rectangle drawRoundRect(int x, int y, int w, int h, int aw, int ah); fillRoundRect(int x, int y, int w, int h, int aw, int ah);

16. 16 TestFigurePanel This example develops a useful class for displaying various figures.

17. 17 Drawing Arcs drawArc(int x, int y, int w, int h, int angle1, int angle2); fillArc(int x, int y, int w, int h, int angle1, int angle2); Angles are in degree

18. 18 Drawing Arcs Example

19. 19 Drawing Polygons and Polylines g.drawPolygon(x, y, x.length); int[] x = {40, 70, 60, 45, 20}; int[] y = {20, 40, 80, 45, 60}; g.drawPolyline(x, y, x.length);

20. 20 Drawing Polygons Using the Polygon Class Polygon polygon = new Polygon(); polygon.addPoint(40, 59); polygon.addPoint(40, 100); polygon.addPoint(10, 100); g.drawPolygon(polygon);

21. 21 Drawing Polygons Example

22. 22 Displaying Image Icons You learned how to create image icons and display image icons in labels and buttons. For example, the following statements create an image icon and display it in a label: ImageIcon icon = new ImageIcon("image/us.gif"); JLabel jlblImage = new JLabel(imageIcon); An image icon displays a fixed-size image.

23. 23 Displaying Image Icons To display an image in a flexible size, you need to use the java.awt.Image class. An image can be created from an image icon using the getImage() method as follows: Image image = imageIcon.getImage();

24. 24 Displaying Images Using a label as an area for displaying images is simple and convenient, but you don't have much control over how the image is displayed. A more flexible way to display images is to use the drawImage method of the Graphics class on a panel. Four versions of the drawImage method are shown here.

25. 25 Displaying Images Example

26. 26 Swing Timers A Swing timer fires one or more action events after a specified delay. You can use Swing timers in two ways:  To perform a task once, after a delay.  To perform a task repeatedly.

27. 27 Swing Timers When you create the timer, you specify an action listener to be notified when the timer "goes off". The actionPerformed method in this listener should contain the code for whatever task you need to be performed. When you create the timer, you also specify the number of milliseconds between timer firings.

28. 28 Swing Timers If you want the timer to go off only once, you can invoke setRepeats(false) on the timer. To start the timer, call its start() method. To suspend it, call stop(). EX Timer timer = new Timer(speed, Listener object); timer.setInitialDelay(pause); //time before invoke the first listener method timer.start();

29. 29 Test Timer Example

30. Any Question 30