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Chapter 5 Graphics. Topics Applets Classes used for graphics –Graphics –Point –Dimension –Color.

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Presentation on theme: "Chapter 5 Graphics. Topics Applets Classes used for graphics –Graphics –Point –Dimension –Color."— Presentation transcript:

1 Chapter 5 Graphics

2 Topics Applets Classes used for graphics –Graphics –Point –Dimension –Color

3 Applets A Java application is a stand-alone program with a main method (like the ones we've seen so far) A Java applet is a program that is intended to transported over the Web and executed using a web browser –An applet also can be executed using the appletviewer tool of the Java Software Development Kit –An applet doesn't have a main method –Instead, there are several special methods that serve specific purposes

4 Applets The paint method, for instance, is executed automatically and is used to draw the applet’s contents The paint method accepts a parameter that is an object of the Graphics class

5 Applets The class that defines an applet extends the Applet class An applet is embedded into an HTML file using a tag that references the bytecode file of the applet class The bytecode version of the program is transported across the web and executed by a Java interpreter that is part of the browser

6 The HTML applet Tag The Einstein Applet

7 Graphics Classes We introduce four standard classes related to drawing geometric shapes on a window: –java.awt.Graphics –java.awt.Color –java.awt.Point –java.awt.Dimension

8 Graphics Class Frames and windows have a graphics context associated with them. A Graphics object defines a graphics context on which we can draw shapes and text The Graphics class has several methods for drawing shapes We can draw geometric shapes on a frame window by calling appropriate methods of the java.awt.Graphics class.

9 Drawing a Line X Y 10 20 150 45 page.drawLine (10, 20, 150, 45); page.drawLine (150, 45, 10, 20); or

10 drawRect How the position of the rectangle is determined by the drawRect method. g.drawRect(50, 50, 100, 30);

11 Graphics Methods

12 Drawing an Oval X Y g.drawOval (175, 20, 50, 80); 175 20 50 80 bounding rectangle

13 Drawing an Arc An arc is a part of an oval To draw you need to specify –the bounding rectangle for the entire oval –the starting angle (measured from the x-axis in degrees –the angle the arc subtends g.drawArc (175, 20, 50, 80, 20, 90);

14 Color Class The java.awt.Color class allows us to designate the color of an object. The RGB scheme combines three values ranging from 0 to 255 for red, green, and blue. Color pinkColor; pinkColor = new Color(255,175,175)

15 RGB Color The Color class also contains several static predefined colors, including: Object Color.cyan Color.white Color.yellow RGB Value 0, 0, 0 0, 0, 255 0, 255, 255 255, 200, 0 255, 255, 255 255, 255, 0

16 Color Class There are public class constants defined in the Color class for common colors: – – – –Color.magenta –

17 The Color Class Every drawing surface has a background color g.setBackground(Color.white); Every graphics context has a current foreground color –The most recently set foreground color is what is used for drawing g.setColor(; g.drawRect(50, 50, 100, 30);

18 Point class A java.awt.Point object designates a point in two-dimensional space. The Point class has public instance variables To assign the position (10, 20) to a Point: Point pt = new Point(); pt.x = 10; pt.y = 20;

19 Dimension Class The java.awt.Dimension class can be used to create bounding rectangles that surround shapes. Dimension dim = new Dimension(); dim.width = 40; dim.height = 70; Bounding rectangles

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