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Creating Graphics in Java

Creating Graphics in Java. CSE301 University of Sunderland Harry R Erwin, PhD. Resources. Flanagan, David (2000). Java Foundation Classes in a Nutshell, O’Reilly. Darwin, Ian F. (2004). Java Cookbook, O’Reilly. Flanagan, David (2004). Java Examples in a Nutshell, O’Reilly.

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Creating Graphics in Java

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  1. Creating Graphics in Java CSE301 University of Sunderland Harry R Erwin, PhD

  2. Resources • Flanagan, David (2000). Java Foundation Classes in a Nutshell, O’Reilly. • Darwin, Ian F. (2004). Java Cookbook, O’Reilly. • Flanagan, David (2004). Java Examples in a Nutshell, O’Reilly.

  3. Java GUI Frameworks • Abstract Window Toolkit (java.awt) • The original set of windowing components designed for Java. These were implemented as separate processes using the GUI features of the underlying operating system. • Swing (or Java Foundation Classes—javax.swing) • A second generation set of ‘light-weight’ windowing components introduced in Java 1.2. These were implemented as Java threads and so avoided the overhead of process context switches and enforced a common look and feel. • SWT (part of Eclipse) • Discussed at: http://java.sun.com/docs/books/tutorial/uiswing/index.html

  4. Goals • The goal of these two lectures is to provide the student an understanding of graphics in Java. • GUI1 explores the Java 2D API, the basic graphics primitives. • GUI2 explores image processing, image I/O, and animation.

  5. Review of AWT • The foundation of GUI in Java • Implemented in separate processes • Rudimentary • Supported by most web browsers, so that most applets should use AWT instead of Swing.

  6. AWT Graphics Features • Basic facilities for creating a graphical user interface. • Drawing graphics • java.awt.Graphics • java.awt.Color • java.awt.Font • Java 2D API (added in Java 1.2) • java.awt.Graphics2D

  7. Using AWT • Import: • java.awt.* • java.awt.event.* • Everything inherits from java.awt.Component, including graphics. • The AWT GUI is organized by containers, inheriting from java.awt.Container (which inherits from Component). • The arrangement of controls is managed by various layout managers. • Notification of changes is handled by events and event listeners that run in a GUI thread.

  8. Graphics Before Java 1.2 • Demonstrated in GraphicsSampler.java from Java Examples in a Nutshell (library). • init() is called to initialise color resources. • paint() is called every time the object needs to be redrawn, for example when the applet is covered by another window and the window moves or disappears.

  9. The Graphics Object • Used for all graphics operations prior to 1.2 • Represents a drawing surface. Can be used to draw on a Component, Image, or printer. • Keeps track of the current state. • Provides attributes and methods for drawing.

  10. java.awt.Graphics • An interface. • Cannot be created directly. You must: • use getGraphics() on a Component • use getGraphics() on an image or PrintJob • copy from an existing Graphics object using create(). • When no longer needed, call dispose() on it to free up the system resources it uses.

  11. Graphics Attributes • Color, the current Color object • Font, the current Font object • Clipping region, the Rectangle to be painted • Origin, a point • Paint mode, a boolean • Background color, a Color

  12. drawLine() (1 pixel) drawPolyLine() (polygon) drawArc() drawOval() drawPolygon() drawRect() drawRoundRect() draw3DRect() fillArc() fillOval() fillPolygon() (polygon) fillRect() fillRoundRect() fill3DRect() drawBytes() (byte[]) drawChars() (char[]) Graphics Operations

  13. drawString() drawImage() various versions, requiring an ImageObserver object clearRect() various setters and getters copyArea() clipRect() translate() hitClip() translate() More Graphics Operations

  14. java.awt.Font • Represents a font. The constructor is passed a name, a style (PLAIN, BOLD, ITALIC, BOLD+ITALIC), and a font size. • Names include: • “serif” • “sansserif” • “monospaced” • “Dialog” • “DialogInput” • “Symbol”

  15. java.awt.Color • Represents colors. • Can represent a color coded in RGB space defined from integers or floating point numbers. • Has a static method that allows you to create colors in the HSB color space. • Provides some standard colors as constants, such as Color.black or Color.white. • java.awt.SystemColor is a subclass with constants for various colors used on the system desktop.

  16. java.awt.Rectangle • Defines a rectangle using the x and y coordinates of the upper left corner and the width and height. These four values are public and can be manipulated directly. • Used to define rectangular regions, usually in an image being manipulated. • Can be used for other purposes.

  17. java.awt.Point • A concrete subclass of java.awt.geom.Point2D • A Point is defined as two integers, x and y. These are public fields and can be manipulated directly. • equals() is overridden so two points are equal if they have the same x and y values. • hashCode() doesn’t appear to be overridden, so don’t use a Point as an index in a HashMap with the expectation that it will be a value class.

  18. This Week’s Exercise • Access http://www.oreilly.com/catalog/jenut3 • Download the sample code and create an Eclipse project for GraphicsSampler.java (an Applet) • Run the Applet in the debugger so you can observe how it works.

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