Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved COS240 Object-Oriented Languages AUBG, COS dept, Spring semester 2012 Reference books: Budd A., An Introduction to Object-Oriented Programming, Addison-Wesley Publ. Com., 3 rd ed Booch Grady et al, Object-Oriented Analysis and Design with Applications, Addison-Wesley Publ. Com., 3 rd ed Course lecturer: Assoc. Prof. Stoyan Bonev, PhD

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved COS240 O-O Languages AUBG, COS dept Lecture 19 Title: Graphics with Java Reference: COS240 Syllabus

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Motivations If you want to draw shapes such as a bar chart, a clock, or a stop sign, as shown below, how do you do it?

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Lecture contents F To understand Java coordinate systems. F To draw things using the methods in the Graphics class. F To understand how and when a Graphics object is created. F To override the paintComponent method to draw things on a GUI component. F To use a panel as a canvas to draw things. F To draw strings, lines, rectangles, ovals, arcs, and polygons. F To obtain font properties using FontMetrics and know how to center a message. F To display image in a GUI component. F To develop reusable GUI components FigurePanel, MessagePanel, StillClock, and ImageViewer.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Java Coordinate System

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Each GUI Component Has its Own Coordinate System

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics class The Graphics class provides the methods for drawing –Strings –Lines –Rectangles –Ovals –Arcs –Polygons –Polylines F 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 (e.g., a button, a label, a panel)

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics Class You can draw strings, lines, rectangles, ovals, arcs, polygons, and polylines, using the methods in the Graphics class. You can apply the methods in the Graphics class to draw things on a GUI component (e.g., a button, a label, a panel)

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics class The Graphics class is an abstract class that provides a device-independent graphics interface for displaying figures and images on the screen on different platforms. Whenever a component (e.g., a button, a label, a panel) is displayed, the JVM automatically creates a Graphics object for the component on the native platform and passes this object to iinvoke the paintComponent() method to display the drawings. the method is defined in JComponent class with signature as follows: protected void paintComponent(Graphics g) This method is invoked whenever a component is first displayed or redisplayed

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics class: practical hints F In order to draw things on a component, you need to define a class that extends JPanel and overrides its paintComponent() method (inherited from JComponent) to specify what to draw.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics class: practical hints F One recommended application skeleton includes: –Import directives –User specified class to extend JFrame u class myFrame extends JFrame { … } –User specified test class to include main() method u public class TestGraphics { … } –User specified class to extend JPanel u class CanvasToDraw extends JPanel { … } F See next slide for details

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The Graphics class: practical hints import javax.swing.*; import java.awt.*; class myFrame extends JFrame { public myFrame() { setTitle("SB GraphicsTest1"); add(new CanvasToDraw()); // getContentPane().add(new CanvasToDraw()); } public class GraphicsTest { public static void main(String[] args) { myFrame frame = new myFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(200, 200); frame.setLocationRelativeTo(null); // Center the frame frame.setVisible(true); } class CanvasToDraw extends JPanel { protected void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.BLUE); g.drawLine(0, 0, 200, 200); g.setColor(Color.RED); g.drawLine(200, 0, 0, 200); }

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved A Drawing Example, using paintComponent method Draw two lines File GraphicsTest.java

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved A Drawing Example, using paint method import javax.swing.*; import java.awt.*; import java.awt.event.*; public class JDemoLine extends JFrame { public void paint(Graphics g) { super.paint(g); g.setColor(Color.BLUE); g.drawLine(0, 0, 200, 200); g.setColor(Color.RED); g.drawLine(200, 0, 0, 200); } public static void main(String[] args) { JDemoLine frame = new JDemoLine(); frame.setTitle("SB Demo Line"); frame.setSize(200, 200); frame.setVisible(true); }

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved A Drawing Example, using paint method Draw two lines File JDemoLine.java

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Problems With the paint() method F If you resize the frame, the line is gone.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The paintComponent Method 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. The paintComponent method is automatically invoked to paint graphics whenever the component is first displayed or redisplayed. Invoking super.paintComponent(g) invokes the paintComponent method defined in the superclass. This is necessary to ensure that the viewing area is cleared before a new drawing is displayed.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved paintComponent Example The JVM invokes paintComponent to draw things on a component. The user should never invoke paintComponent directly. For this reason, the protected visibility is sufficient for paintComponent.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing on Panels F Panels are invisible and are used as containers to group components to achieve a desired layout. F Another important use of JPanel is for drawing. F You can draw on any Swing GUI component, but normally you should use a JPanel as a canvas upon which to draw things  See next slide.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing on Panels F What happens if you replace JPanel with JLabel or JButton in following line –class CanvasToDraw extends JPanel { F With –class CanvasToDraw extends JLabel { F Or with –class CanvasToDraw extends JButton { F The program works, but it is not preferred. JLabel is designed for creating a label, not for drawing. Same for JButton is designed for creating a button, not for drawing.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing on Panels F 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. You can then display strings, draw geometric shapes, and view images on the panel. F Compile and run TestGraphics.java

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Geometric Figures F Drawing Strings F Drawing Lines F Drawing Rectangles F Drawing Ovals F Drawing Arcs F Drawing Polygons

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Strings drawLine(int x1, int y1, int x2, int y2);drawString(String s, int x, int y);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Rectangles drawRect(int x, int y, int w, int h); fillRect(int x, int y, int w, int h);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Rounded Rectangles 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);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Ovals drawOval(int x, int y, int w, int h); fillOval(int x, int y, int w, int h);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved 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

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Arcs Example DrawArcsRun

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Polygons and Polylines int[] x = {40, 70, 60, 45, 20}; int[] y = {20, 40, 80, 45, 60}; g.drawPolygon(x, y, x.length); g.drawPolyline(x, y, x.length);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved 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);

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Drawing Polygons Example DrawPolygon Run

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Centering Display Using the FontMetrics Class You can display a string at any location in a panel. Can you display it centered? To do so, you need to use the FontMetrics class to measure the exact width and height of the string for a particular font. A FontMetrics can measure the following attributes: F public int getAscent() F public int getDescent() F public int getLeading() getAscent() getLeading() getDescent() getHeight() F public int getHeight() F public int stringWidth(String str)

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved The FontMetrics Class FontMetrics is an abstract class. To get a FontMetrics object for a specific font, use the following getFontMetrics methods defined in the Graphics class: · public FontMetrics getFontMetrics(Font f) Returns the font metrics of the specified font. · public FontMetrics getFontMetrics() Returns the font metrics of the current font.

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved

Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved Thank You for Your attention!