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Graphics and Java2D

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  • 1. Java I--Copyright © 2000 Tom Hunter
  • 2. Java I--Copyright © 2000 Tom Hunter Chapter 11 Graphics and Java2D
  • 3. Java I--Copyright © 2000 Tom Hunter The Origins of the GUI in Java
  • 4. Java I--Copyright © 2000 Tom Hunter • When Java 1.0 was first rolled out, it only contained the AWT, for Abstract Window Toolkit, for basic GUI programming. The Origins of the GUI in Java
  • 5. Java I--Copyright © 2000 Tom Hunter • The original AWT lacked many features that one would expect in an Object-Oriented Toolkit: —clipboards, —support for printing and —keyboard navigation. • The AWT even lacked Popup menus and Scroll Panes—things no modern GUI developer could live without. The Origins of the GUI in Java
  • 6. Java I--Copyright © 2000 Tom Hunter • In a word, the AWT sucked. The Origins of the GUI in Java Why?Why? The original AWT deals with GUI elements by not dealing with them. It delegates their creation and behavior to the native GUI toolkit on each target platform. We say the underlying “Peer” text box actually handles the GUI.
  • 7. Java I--Copyright © 2000 Tom Hunter • Definition: Peers are native GUI components that are manipulated by the AWT classes. 1.) You want to create an instance of the Menu class, the Java runtime system creates an instance of the menu peer. 2.) The menu peer does the real work of of displaying and managing the menu behavior. The Origins of the GUI in Java
  • 8. Java I--Copyright © 2000 Tom Hunter Java Program Java AWT Native Windowing System Peers Display How peers fit into the process of displaying components in native windowing systems.
  • 9. Java I--Copyright © 2000 Tom Hunter • Under “peer” architecture, the peer—the underlying operating system—takes care of painting windows and reacting to events. • Under this system, the AWT is like a Lazy Construction Supervisor who attempts to look busy while he delegates all the real work to the harried Construction Worker Bees (Peers). The Origins of the GUI in Java
  • 10. Java I--Copyright © 2000 Tom Hunter • The ease of peer architecture allowed the early developers to crank out AWT “components” that really didn’t do much. The Origins of the GUI in Java (The original AWT was developed in six weekssix weeks.)
  • 11. Java I--Copyright © 2000 Tom Hunter • This style of architecture means that each platform’s native window actually renders the window, and from the diagram, you can see why we call them “heavyweight”—a lot is happening. • This also means slow performance. • And, every peer on a different Operating System produces a different result. The Origins of the GUI in Java
  • 12. Java I--Copyright © 2000 Tom Hunter • Therefore, if you used AWT on a Windows machine, your GUI looked like Windows. • If you used AWT on a Macintosh, your GUI looked like Macintosh. • If you used AWT on an X11/Motif machine, your GUI crashed and burned. The Origins of the GUI in Java
  • 13. Java I--Copyright © 2000 Tom Hunter (X11/Motif machines could not support complex graphical elements such as menus and scrollbars.) • So, using the original AWT GUI, you found that your application looked completely different on the various platforms and, what was worse, it encountered different bugs on different platforms, such as the ones on Motif. • These bugs came from mismatches between the peers and the AWT components. The Origins of the GUI in Java
  • 14. Java I--Copyright © 2000 Tom Hunter • Developers were forced to test their applications on each platform, a practice that became infamously known as… … write once, debugdebug everywhere... The Origins of the GUI in Java
  • 15. Java I--Copyright © 2000 Tom Hunter • A year after Java 1.0 came out, Netscape created a Java GUI library called the IFC { Internet Foundation Classes } that used a fresh approach. The Origins of the GUI in Java
  • 16. Java I--Copyright © 2000 Tom Hunter • The IFC was a set of lightweight classes based on ideas from NEXTSTEP’s User Interface Toolkits. • The IFCs did not rely on peers. • Javasoft, fearing that the Java community would fracture because of the new IFC, made a deal with Netscape to adapt the IFC. The Origins of the GUI in Java
  • 17. Java I--Copyright © 2000 Tom Hunter • Using the IFC approach, User Interface Components (buttons, menus, textboxes—called Widgets) were painted onto blank windows. • The only peer functionality needed was a way to put up windows and paint on the window. The Origins of the GUI in Java
  • 18. Java I--Copyright © 2000 Tom Hunter • Netscape’s IFC widgets looked and behaved the same no matter which platform they ran on. • Sun accepted Netscape’s lead on this process and created a new user interface library named after a Duke Ellington songDuke Ellington song: “It Don’t Mean A Thing If It Ain’t Got That Swing…” The Origins of the GUI in Java
  • 19. Java I--Copyright © 2000 Tom Hunter • Swing is now the official name for the non-peer-based GUI toolkit that is part of the Java Foundation Classes (JFC). • Because Swing was not part of the original core Classes, but rather, was an extension, it was named javax.swing. The Origins of the GUI in Java
  • 20. Java I--Copyright © 2000 Tom Hunter • Thus, the AWT library is still used, especially the version 1.1 Event Handling library. • Swing elements are somewhat slower than their AWT counterparts, so the AWT elements are still valuable. The Origins of the GUI in Java • The AWT library of classes is still needed to this day—Swing is built on AWT.
  • 21. Java I--Copyright © 2000 Tom Hunter AWT Frame, Window, Dialog Component, Container, Graphics, Color, Font, Toolkit, Layout Managers Swing Heavyweight Swing Lightweight Components (very few) Components • Swing’s Relationship to the AWT
  • 22. Java I--Copyright © 2000 Tom Hunter • Swing takes advantage of the AWT’s infrastructure, including graphics, colors, fonts toolkits and layout managers. • Swing does NOT use the AWT’s components. • Of all the components the AWT has to offer, Swing uses only Frame, Window and Dialog, as the Superclasses to JFrame, JWindow and JDialog. The Origins of the GUI in Java
  • 23. Java I--Copyright © 2000 Tom Hunter • In effect, Swing cherry picked the best of the AWT to build a new set of mostly lightweight components, while discarding the parts of AWT that were the most trouble—the heavyweight components. • Swing was intended to replace the AWT’s heavyweight components, but not the AWT itself. • Thus, in order to understand the Swing GUI library (next week), we need to understand the AWT library first. The Origins of the GUI in Java
  • 24. Java I--Copyright © 2000 Tom Hunter Lightweight versus Heavyweight
  • 25. Java I--Copyright © 2000 Tom Hunter • The 1.1 API introduced the notion of lightweight components. • Lightweight components directly extend either: java.awt.Component or java.awt.Container • The Component class and its supporting cast are the foundation upon which the AWT is built. Lightweight versus Heavyweight
  • 26. Java I--Copyright © 2000 Tom Hunter • Component—an abstract base class for components such as menus, buttons, labels and lists. • Container—an abstract base class that extends Component. Classes derived from Container are Panel, Applet, Window, Dialog and Frame. All can contain multiple components. Lightweight versus Heavyweight
  • 27. Java I--Copyright © 2000 Tom Hunter • Component—these are the small pieces. • Container—these are the boxes. Containers may contain Components. Lightweight versus Heavyweight
  • 28. Java I--Copyright © 2000 Tom Hunter Lightweight versus Heavyweight • LayoutManager—an interface that defines methods for positioning and sizing objects within a container. • Graphics—an abstract class that defines methods for performing graphical operations in a component. Every component has an associated Graphics object.
  • 29. Java I--Copyright © 2000 Tom Hunter Image-Observer interface Container Component M 1 LayoutManager interface All* Containers come equipped with a layout manager, which positions and shapes the container’s components. * java.awt.Container does not have a layout manager
  • 30. Java I--Copyright © 2000 Tom Hunter • Component is an abstract class that provides a great deal of functionality for the classes that extend it. For example, a Component has the following affiliated with it. —Graphics object —Location —Size —Native peer —Parent container —Fonts and font dimensions ( font metrics) —Foreground and Background colors —Locale —Minimum, Maximum and Preferred sizes Lightweight versus Heavyweight
  • 31. Java I--Copyright © 2000 Tom Hunter • A Component does not decide for itself how it will be shaped, and so its shape ends up taking a lot of abuse. • Now, before you go blaming Container for this abuse, you must know that Container is an innocent bystander. • Although a Container contains a Container , it is the LayoutManagerLayoutManager who is 100% responsible for the abuse dished out to a Container . The LayoutManagerLayoutManager decides the sizing and positioning of components.
  • 32. Java I--Copyright © 2000 Tom Hunter • Container can contain multiple Components. • Using Containers, you can group related components and treat them as a unit. • This simplifies an applet’s design and is useful for arranging components on the display. Lightweight versus Heavyweight
  • 33. Java I--Copyright © 2000 Tom Hunter Applet—an extension of Panel. Dialog—an extension of Window. Modal or NonModal. FileDialog—a Dialog for selecting a file. Frame—an extension of Window—the Container for an Application. Panel—an extension of Container. Panel—a simple container. ScrollPane—scrolls. Window—an extension of Container, windows have no menu or border. Rarely extended. Superclass of Frame and Dialog.
  • 34. Java I--Copyright © 2000 Tom Hunter Layout Managers • Containers merely keep track of what Components they contain. • They delegate the positioning and shaping of their components to a layout manager. Lightweight versus Heavyweight
  • 35. Java I--Copyright © 2000 Tom Hunter Layout Managers • The LayoutManager interface defines methods for laying out components and calculating the preferred and minimum sizes of their containers. • The AWT provide five classes that implement either the LayoutManager or LayoutManager2 interfaces. Lightweight versus Heavyweight
  • 36. Java I--Copyright © 2000 Tom Hunter • FlowLayout—specifies that components flow left to right, top to bottom. • BorderLayout—lays out North/South/East/West/Center components. • CardLayout—displays one panel at a time from a deck of panels. • GridLayout—lays out components on a simple grid. Components are stretched to fill the grid. • GridBagLayout—imposes constraints on each component in a grid. Lightweight versus Heavyweight We will learn a lot about the GridBagLayout, which is the most important layout manager.
  • 37. Java I--Copyright © 2000 Tom Hunter Flow Layout
  • 38. Java I--Copyright © 2000 Tom Hunter • FlowLayout—Displays components left to right, top to bottom. FlowLayout is the default layout manager for panels and applets. Flow Layout • When Should You Use It? —Use it when you aren’t too concerned about appearance.
  • 39. Java I--Copyright © 2000 Tom Hunter • This just shoves in the components willy-nilly. —When an instance of FlowLayout is constructed, the alignment (LEFT, CENTER, RIGHT) can be specified, in addition to horizontal and vertical gaps. —The horizontal and vertical gaps specify not only the gaps between components but also between the edges of the components and the sides of the container. (This of course is in direct contrast to the BorderLayout, where the gaps are only between components.) Flow Layout
  • 40. Java I--Copyright © 2000 Tom Hunter Border Layout
  • 41. Java I--Copyright © 2000 Tom Hunter • BorderLayout—Lays out components around the sides and in the center of the container in North, East, South, West and Center positions. —Gaps between components can be specified. BorderLayout is the default layout manager for Window, Dialog and Frame. Border Layout
  • 42. Java I--Copyright © 2000 Tom Hunter • BorderLayout is by far the most frequently used layout manager. —It is the default manager for most of the AWT containers. Container Class Default Layout Manager Border Layout Container null Panel FlowLayout Window BorderLayout Dialog BorderLayout Frame BorderLayout
  • 43. Java I--Copyright © 2000 Tom Hunter Border Layout • When Should You Use It? —Use it when a Container divides its components into regions: North and South, East and West. • Once you’ve created a few nested layouts, using panels to join components into sub-panels, you’ll appreciate the quick convenience of the BorderLayout, which sets components (or groups of them) into geographical regions. • Nearly every nested layout has a BorderLayout lurking somewhere inside.
  • 44. Java I--Copyright © 2000 Tom Hunter Border Layout • Here is an example that shows how you can specify the horizontal and vertical gaps between the components: BorderLayout borlay = new BorderLayout( 2, 2 ); horizontal gap vertical gap
  • 45. Java I--Copyright © 2000 Tom Hunter Card Layout
  • 46. Java I--Copyright © 2000 Tom Hunter • CardLayout—displays one component at a time from a deck of components. —Components can be swapped in and out. Card Layout • When Should You Use It? —Use it when you want to control the visibility of a set of components under different circumstances. —Use it when a set of panels present themselves as a stack of Tabbed Folders.
  • 47. Java I--Copyright © 2000 Tom Hunter • From this deck of components, you can display or deal any one container at a time. Card Layout • You use this for containers such as a tabbed panel. • This layout manager allows clients to control which component is currently displayed. • The CardLayout manager is unique in that you can directly control which component is displayed at any one time.
  • 48. Java I--Copyright © 2000 Tom Hunter • CardLayout Stacking Methods: Card Layout void first( Container ) void last( Container ) void next( Container ) void previous( Container ) —displays the first component added to the container —displays the last component added to the container. —displays the component added to the container after the currently displayed component. If the current component is the first, then the last component is displayed. —displays the component added to the container before the currently displayed component. If the current component is the first, then the last is shown.
  • 49. Java I--Copyright © 2000 Tom Hunter • CardLayout Stacking Methods: Card Layout void show( Container, String ) —shows the component whose name matches the String passed in. If no components match the name, the method does nothing. —the CardLayout is instantiated with a horizontal gap of 10 pixels and a vertical gap of 5 pixels. Since only one component can be displayed at a time, the gaps specify a margin around the components, rather than between the components, as is the case with the BorderLayout.
  • 50. Java I--Copyright © 2000 Tom Hunter Grid Layout
  • 51. Java I--Copyright © 2000 Tom Hunter • GridLayout—Lays out components in a grid, with each component stretched to fill its grid cell. —Horizontal and vertical gaps between components can be specified. Grid Layout • When Should You Use It? —Use it when you need to create something like a calendar or a spreadsheet.
  • 52. Java I--Copyright © 2000 Tom Hunter • You can set up the number of rows and columns it contains either at the time of instantiation, or anytime thereafter. GridLayout gl = new GridLayout( 3, 0, 10, 10 ); Grid Layout rows columns (Zero means the number total is computed) horizontal gap vertical gap
  • 53. Java I--Copyright © 2000 Tom Hunter GridBag Layout
  • 54. Java I--Copyright © 2000 Tom Hunter • GridBagLayout—Arranges components in a grid using an elaborate set of grid constraints. GridBag Layout This layout manager isThis layout manager is tested heavily in anytested heavily in any certification exam.certification exam.
  • 55. Java I--Copyright © 2000 Tom Hunter • GridBagLayout—Arranges components in a grid using an elaborate set of grid constraints. GridBag Layout • When Should You Use It? —Use it when you’re building complicated input forms, such as a container that has components for name, address, city, state and zip.
  • 56. Java I--Copyright © 2000 Tom Hunter • Unlike GridLayout, where you explicitly specify the number of rows and columns in the grid, the GridBagLayout itself determines the number of rows and columns from constraints placed upon the components it lays out. —Also, unlike GridLayout, GridBagLayout allows components to span more than one rigid cell. —Components may also overlap. GridBag Layout
  • 57. Java I--Copyright © 2000 Tom Hunter • The GridBagLayout is one of the toughest and most complex in all of AWT. Therefore, we will use divide and conquer to learn it. GridBag Layout
  • 58. Java I--Copyright © 2000 Tom Hunter /** * Creates a <code>GridBagConstraint</code> object with * all of its fields set to their default value. * @since JDK1.0 */ public GridBagConstraints () { gridx = RELATIVE; gridy = RELATIVE; gridwidth = 1; gridheight = 1; weightx = 0; weighty = 0; anchor = CENTER; fill = NONE; insets = new Insets(0, 0, 0, 0); ipadx = 0; ipady = 0; }
  • 59. Java I--Copyright © 2000 Tom Hunter • To describe the factors that limit the placement of components in a GridBagLayout, we use a special class called the GridBagConstraints. —When you are adding components to a container that has been set up with a GridBagLayout, you: 1.) Set up the constraints in the object of type GridBagConstraints 2.) Set the constraints for your object using the GridBagConstraints object. 3.) Add the object whose constraints you just set. GridBag Layout: GridBagConstraints
  • 60. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBag Layout: GridBagConstraints
  • 61. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBag Layout: GridBagConstraints Usually, with the other layout managers, we don’t bother to make a named object. However, in this case, it makes sense
  • 62. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); GridBag Layout: GridBagConstraints Now, we have merely instantiated an object gbcon of type GridBagConstraints.
  • 63. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); GridBag Layout: GridBagConstraints There is nothing unusual about this—just setting getting a content pane and using it to instantiate a container.
  • 64. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbl.setConstraints( butt, gbcon ); GridBag Layout: GridBagConstraints Between the previous step and this step there is a step missing. We would have had to set instance variables for the way we would like the constraints to be for this particular button. We’ll delay defining the actual constraints for a few minutes.
  • 65. Java I--Copyright © 2000 Tom Hunter • Let’s take this really slowly: JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbl.setConstraints( butt, gbcon ); c.add( butt ); GridBag Layout: GridBagConstraints Using a different method of the container, we could have combined these last two steps.
  • 66. Java I--Copyright © 2000 Tom Hunter • Now, the missing steps: set the constraints: • These are the instance variables of class GridBagConstraints that we could have set before we added our JButton butt to the container: —gridx —gridy These are used to specify the row and column for the upper-left hand corner of the component. Default value: GridBagConstraints.RELATIVE GridBag Layout: GridBagConstraints
  • 67. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.gridx = 0; gbcon.gridy = 1; gbl.setConstraints( butt, gbcon ); c.add( butt ); Valid Values: RELATIVE, which means to the previous component, or any integer.
  • 68. Java I--Copyright © 2000 Tom Hunter • These instance variables are used to decide the number of columns (gridwidth) and the number of rows (gridheight) —gridwidth —gridheight These descriptions refer to the number of cells, not the number of pixels. Default value: 1 Whether or not a component fills its allotted grid cells depends on the fill attribute. GridBag Layout: GridBagConstraints
  • 69. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.gridwidth = 2; gbcon.gridheight = 2; gbl.setConstraints( butt, gbcon ); c.add( butt ); Valid Values: GridBagConstraints.RELATIVE (for gridwidth) GridBagConstraints.REMAINDER (for gridheight) or an integer that represents the width and height in grid cells.
  • 70. Java I--Copyright © 2000 Tom Hunter • This anchor is used to make the component stick to an edge of the container it is placed in. —anchor There are a certain number of valid constants you can use for these. Note: if the component entirely fills up its allotted space, you won’t notice its anchor point. Default value: GridBagConstraints.CENTER GridBag Layout: GridBagConstraints
  • 71. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.anchor = GridBagConstraints.NORTH; gbl.setConstraints( butt, gbcon ); c.add( butt ); Valid Values: CENTER EAST NORTH WEST NORTHEAST NORTHWEST SOUTHEAST SOUTHWEST
  • 72. Java I--Copyright © 2000 Tom Hunter • Fill describes the manner in which the component fills the grid cells it occupies. —fill This is used when the component’s size is smaller than the space it is expected to fill. This determines in what way—if any—the component will be stretched. Default value: GridBagConstraints.NONE GridBag Layout: GridBagConstraints
  • 73. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.fill = GridBagConstraints.HORIZONTAL; gbl.setConstraints( butt, gbcon ); c.add( butt ); Valid Values: BOTH HORIZONTAL VERTICAL NONE (DEFAULT)
  • 74. Java I--Copyright © 2000 Tom Hunter • This represents integer values for the number of pixels of internal padding that increases the component’s preferred size. Negative values reduce the preferred size. —ipadx —ipady Default value: 0 GridBag Layout: GridBagConstraints
  • 75. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.ipadx = 5; gbcon.ipady = -2; gbl.setConstraints( butt, gbcon ); c.add( butt );
  • 76. Java I--Copyright © 2000 Tom Hunter • This represents external padding between the edges of the component and the edges of its grid cells. Negative values, which cause the component to extend outside of its grid cells, are allowed. —insets Default value: (0,0,0,0) GridBag Layout: GridBagConstraints
  • 77. Java I--Copyright © 2000 Tom Hunter JButton butt = new JButton( “Hairy” ); GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbcon = new GridBagConstraints(); Container c = getContentPane(); c.setLayout( gbl ); gbcon.insets = new Insets( 0,0,0,0 ); gbl.setConstraints( butt, gbcon ); c.add( butt );
  • 78. Java I--Copyright © 2000 Tom Hunter • This decides how extra space is consumed by the component’s grid cells. Whether or not a component fills its grid cells depends upon the fill attribute. Values must be positive. —weightx —weighty Default value: 0.0 Double values that represent weighting given to a component’s grid cells relative to other components in the same row or column. GridBag Layout: GridBagConstraints
  • 79. Java I--Copyright © 2000 Tom Hunter AWT vs Swing
  • 80. Java I--Copyright © 2000 Tom Hunter • Let’s make a comparison: —since AWT components delegate to a native peer, their behavior cannot be changed or extended. —For example, you cannot put an image on an AWT button because the button is created in C++ and you can’t extend C++. —Because the native window is opaque, the AWT window must also be opaque. AWT vs Swing
  • 81. Java I--Copyright © 2000 Tom Hunter • Because a Swing component doesn’t depend on the underlying operating system, you cancan put an image on a button. • You’re not relying on the native button. AWT vs Swing
  • 82. Java I--Copyright © 2000 Tom Hunter • Conversely, a Swing component can have a transparent background, because it is not depending on the native system to do the work for it. ( As an added plus, the ability to create a transparent background allows lightweight components to appear as non-rectangular, even though ALL components, heavyweight or lightweight, have a rectangular bounding box.) AWT vs Swing
  • 83. Java I--Copyright © 2000 Tom Hunter The Original Class Graphics
  • 84. Java I--Copyright © 2000 Tom Hunter • Now that we grasp the essential difference between AWT and Swing, we will focus on a pair of classes that demonstrate this difference. The Original Class—Graphics
  • 85. Java I--Copyright © 2000 Tom Hunter • First we will focus on the original set of Graphical components, and then move on to the modern Graphics2D class that comes with Swing. • As we said, the original Java 2D API works on the basis of the AWT, Abstract Window Toolkit, which relies on the underlying hardware. The Original Class—Graphics
  • 86. Java I--Copyright © 2000 Tom Hunter • Graphics is an abstract class. What does that mean? The Original Class—Graphics • An Abstract class cannot be instantiated, so then what is going on when we do this? public void paint( Graphics g ) { }
  • 87. Java I--Copyright © 2000 Tom Hunter The Original Class—Graphics public void paint( Graphics g ) { } In this situation, we are actually using a derivedderived class of Graphics—a Subclass of Graphics actually implements the drawing capabilities. Graphics merely supplies the interface, while using heavyweight components to do the heavy lifting. Notice, we never wrote: Graphics g = new Graphics()
  • 88. Java I--Copyright © 2000 Tom Hunter Graphics Basics
  • 89. Java I--Copyright © 2000 Tom Hunter • The Java coordinate system begins in the upper-left- hand side of the screen. • The 0,0 location is actually behind the title bar. Graphics Basics (X,Y)
  • 90. Java I--Copyright © 2000 Tom Hunter • You use the method getInsets() of class Container to detect where you can start drawing. • There are four measurements that tell you how many pixels away from the edge is the available drawing area. Graphics Basics
  • 91. Java I--Copyright © 2000 Tom Hunter Graphics Context
  • 92. Java I--Copyright © 2000 Tom Hunter • A Graphics object remembers a collection of settings for drawing images and text, such as the font you set or the current color. • This collection of settings is known as a Graphics Context. •All drawing in Java must go through this Graphics object, using the established Graphics Context. Graphics Context
  • 93. Java I--Copyright © 2000 Tom Hunter • Before you can draw on the screen, you have to acquire the Graphics context. • Naturally, a Graphics object takes care of acquiring the Graphics context, and uses it to control how information is drawn. Graphics Context
  • 94. Java I--Copyright © 2000 Tom Hunter • A Graphics object encapsulates state variables for: • the Component object on which to draw • information about “clipping” an object, or masking pieces of it. • current color • current font • information about the pixels Graphics Context
  • 95. Java I--Copyright © 2000 Tom Hunter • A Graphics object has methods for: • drawing • font manipulation, and • color manipulation. Graphics Context
  • 96. Java I--Copyright © 2000 Tom Hunter Color
  • 97. Java I--Copyright © 2000 Tom Hunter Color • This class defines methods and constants used to manipulate colors. • Colors are created from: red, green, and blue components.
  • 98. Java I--Copyright © 2000 Tom Hunter Color • RGB values: —3 Integers from 0-255 each. [ This equates to 16.7 million colors.] Alternately, —3 Floating-point values between 0-1.0. • The larger the number, the more of that color is added. Alternately, Can use the Color Constants ( page 517-518)
  • 99. Java I--Copyright © 2000 Tom Hunter Color • Color Constants: RGB Value public final static Color orange 255, 200, 0 Red Green Blue
  • 100. Java I--Copyright © 2000 Tom Hunter Color • Color methods: getRed() getGreen() getBlue() getColor() setColor() This method will return an integer between 0-255 with the amount of Red in the Graphics object. This method will return a Color object with the current color for the graphics context. This method takes a Color object argument and will set the current color for the graphics context.
  • 101. Java I--Copyright © 2000 Tom Hunter Color • You pass a Color object to the method setColor() Color col = new Color( 255, 0, 0 ); g.setColor( col ); Or, g.setColor( new Color( 255, 0, 0 ) );
  • 102. Java I--Copyright © 2000 Tom Hunter Color • You get a Color object from the method getColor() Color x = g.getColor(); Or, g.setColor( new Color( 255, 0, 0 ) ); The 256 x 256 x 256 = 16.7 million color possibilities.
  • 103. Java I--Copyright © 2000 Tom Hunter Color: JColorChooser • Swing offers a special class called a JColorChooser —something AWT never offered. • The JColorChooser opens a predefined color dialog. •This dialog lets you pass arguments that specify which object to change color, a text message and a color object.
  • 104. Java I--Copyright © 2000 Tom Hunter Font
  • 105. Java I--Copyright © 2000 Tom Hunter • The Constructor for class Font takes three arguments: —font name, —font style, and —font size. Font The font name is any one currently supported by the system the program is running on. The font style is any combination of the well-known alternatives Plain/Italic/Bold. Java supplies Class constants: Font.PLAIN Font.ITALIC Font.BOLD The size is measured in points. One point is 1/72nd of an inch.
  • 106. Java I--Copyright © 2000 Tom Hunter public class Fonts extends JFrame { public Fonts() { super( "Using fonts" ); setSize( 420, 125 ); show(); } public void paint( Graphics g ) { g.setFont( new Font( "Serif", Font.BOLD, 12 ) ); g.setFont( new Font( "Monospaced", Font.ITALIC, 24 ) ); } } This is the usual way. This fires the default constructor with the Font Name, the Font Style and the Font Size.
  • 107. Java I--Copyright © 2000 Tom Hunter Font • To display text, you must first select a font. • To select a font, you must first create an object of the class Font. • You specify a font by its font face name ( or font name for short), and its point size. Font cou = new Font( “Courier”, Font.BOLD, 24 ); 24 points (A point is 1/72nd of an inch )
  • 108. Java I--Copyright © 2000 Tom Hunter Font Metrics
  • 109. Java I--Copyright © 2000 Tom Hunter • In some cases, you must know the exact dimensions of the font. • For that end, you seek to know the Font Metrics: FontMetrics
  • 110. Java I--Copyright © 2000 Tom Hunter • The leading, is the space between lines. FontMetrics: Class FontMetrics xylgQ$ leading ascent baseline descent • Class FontMetrics offers methods to return all these metric values in points.
  • 111. Java I--Copyright © 2000 Tom Hunter Drawing Lines, Rectangles and Ovals
  • 112. Java I--Copyright © 2000 Tom Hunter Drawing Lines, Rectangles and Ovals • Class Graphics has a raft of methods that can be used to draw. Single line... drawLine( int x1, int y1, int x2, int y2 ) This will draw a line between the point defined by (x1,y1) and (x2,y2)
  • 113. Java I--Copyright © 2000 Tom Hunter Drawing Lines, Rectangles and Ovals • Draw Rectangles... drawRect( int x1, int y1, int width, int height ) This will draw a rectangle with the top- left-hand corner (x1,y1) with the width and height specified.
  • 114. Java I--Copyright © 2000 Tom Hunter Drawing Lines, Rectangles and Ovals • Draw a rectangle with a filled-in center... fillRect( int x1, int y1, int width, int height ) This will draw a filled rectangle with the top- left-hand corner (x1,y1) with the width and height specified.
  • 115. Java I--Copyright © 2000 Tom Hunter Drawing Lines, Rectangles and Ovals • Draw a rectangle with the same color as the background color... clearRect( int x1, int y1, int width, int height ) This will draw a filled rectangle with the top-left-hand corner (x1,y1) with the width and height specified, with the same color as the background color. Page 531
  • 116. Java I--Copyright © 2000 Tom Hunter Drawing Arcs
  • 117. Java I--Copyright © 2000 Tom Hunter Drawing Arcs • An arc is a portion of a circle. • An arc is drawn in an imaginary box, whose size we specify. • An arc has a degree that it starts from, and a number of degrees that it sweeps.
  • 118. Java I--Copyright © 2000 Tom Hunter Drawing Arcs • Contrary to intuition, a positive number of degrees for the sweep describes an arc that goes counter clockwise • Likewise, a negative number of degrees for the sweep describes an arc that goes clockwise.
  • 119. Java I--Copyright © 2000 Tom Hunter • There are two primary methods at work: drawArc( int x, int y, int width, int height, int startAngle, int arcAngle ) x, y Drawing Arcs Obviously, it doesn’t matter which way you draw the arc. You can start from 0 degrees and go negative, or start from 90 degrees and go positive. positive negative
  • 120. Java I--Copyright © 2000 Tom Hunter • You must set the color with a different method. fillArc( int x, int y, int width, int height, int startAngle, int arcAngle ) x, y Drawing Arcs
  • 121. Java I--Copyright © 2000 Tom Hunter Drawing Polygons and Polylines
  • 122. Java I--Copyright © 2000 Tom Hunter Drawing Polygons and Polylines • A polygon is a complex, multisided shape. • A polyline is a complex, multi-angled line.
  • 123. Java I--Copyright © 2000 Tom Hunter Drawing Polygons and Polylines • This draws a closed shape, even if the locations of the points do not make that occur. • So, no matter where you place the points, the shape is closed. drawPolygon( int xPoints[], int yPoints[], int points ) • drawPolygon also has a constructor that takes another polygon object drawPolygon( Polygon p ) fillPolygon( int xPoints[], int yPoints[], int points ) • For the fill, you have to issue a separate method call.
  • 124. Java I--Copyright © 2000 Tom Hunter Drawing Polygons and Polylines • This draws a series of lines that are connected. • In this case, if you do not make sure the last point coincides with the first, then the shape enclosed by the polylines is not closed. drawPolyline( int xPoints[], int yPoints[], int points ) If the number of points is less than the number of coordinates, no problem. If the number of points is greater than the number of coordinates, it throws an exception: ArrayIndexOutOfBoundsExcception
  • 125. Java I--Copyright © 2000 Tom Hunter Class Graphics versus Graphics2D
  • 126. Java I--Copyright © 2000 Tom Hunter • The awt graphics are used for basic html graphics and are not suitable for complex graphics. For example, Class: Graphics … lets you draw only a very few specific shapes: rectangles, ovals and polygons. Class Graphics versus Graphics2D
  • 127. Java I--Copyright © 2000 Tom Hunter • Class Graphics2D allows you to draw any shape. • Also, Graphics2D , in contrast to the awt package, allows you to decide the style of line you wish to draw, including its width and fill properties—known as a line’s texturetexture. Class Graphics versus Graphics2D
  • 128. Java I--Copyright © 2000 Tom Hunter • To start with, all these Geometric shapes are created starting with: interface Shape • Curves and arcs are created using the same interface. Class Graphics versus Graphics2D
  • 129. Java I--Copyright © 2000 Tom Hunter • To determine the fill style of an object, you use: interface Paint • To determine the pen style of an object, you use: interface Stroke Class Graphics versus Graphics2D
  • 130. Java I--Copyright © 2000 Tom Hunter • First of all, notice that class Graphics is the Superclass to Graphics2D. Class Graphics versus Graphics2D
  • 131. Java I--Copyright © 2000 Tom Hunter • Every time you have used this method: public void paint( Graphics g ) you have in fact been using a Graphics2D object. Class Graphics versus Graphics2D
  • 132. Java I--Copyright © 2000 Tom Hunter • Before you can access the Graphics2D capabilities, you must perform a downcast on the Graphics g reference passed to paint. • This is safe because—trust me—the object is actually of type Graphics2D: public void paint(Graphics g ) — familiar. { Graphics2D g2d = ( Graphics2D ) g; Class Graphics versus Graphics2D Normally, we would hesitate to cast a Superclass reference to a Subclass type, because we know the Subclass is likely to have many methods not present in the Superclass. However, this is safe merely because we know g is really a Subclass object.
  • 133. Java I--Copyright © 2000 Tom Hunter • AnytimeAnytime you wish to convert a Graphics reference into a Graphics2D reference, you must use this downcast. public void paint(Graphics g ) { Graphics2D g2d = ( Graphics2D ) g; Class Graphics versus Graphics2D
  • 134. Java I--Copyright © 2000 Tom Hunter Java2D Shapes
  • 135. Java I--Copyright © 2000 Tom Hunter Java2D Shapes • The following 2D classes come from package: java.awt.geom Ellipse2D.Double Rectangle2D.Double RoundRectangle2D.Double Arc2D.Double Line2D.Double Ellipse2D.Double Rectangle2D.Double RoundRectangle2D.Double Arc2D.Double Line2D.Double When you see the word .Double What does that tell you? First of all, the “.Double” tells us that Double is a static inner class. Each of these classes represent a shape with its dimensions specified as double- precision floating point values.
  • 136. Java I--Copyright © 2000 Tom Hunter Java2D Shapes • There are Float static inner classes in each of these classes. Ellipse2D.Float Rectangle2D.Float RoundRectangle2D.Float Arc2D.Float Line2D.Float
  • 137. Java I--Copyright © 2000 Tom Hunter