Unit - 1 PDF

Chapter 1 (a) : Graphics Programming............................................................. 537 1.1 Introducing Swing..................................................................................... 538 1.2 Creating a Frame.............

Chapter 1 (a) : Graphics Programming............................................................. 537 1.1 Introducing Swing..................................................................................... 538 1.2 Creating a Frame...................................................................................... 543 1.3 Positioning a Frame.................................................................................. 546 1.3.1 Frame Properties........................................................................... 549 1.3.2 Determining a Good Frame Size.................................................. 549 1.4 Displaying Information in a Component.................................................... 554 1.5 Working with 2D Shapes.......................................................................... 560 1.6 Using Color............................................................................................... 569 1.7 Using Special Fonts for Text..................................................................... 573 1.8 Displaying Images.................................................................................... 582 This chapter starts you on the road to writing Java programs that use a graphical user interface (GUI). In particular, you will learn how to write programs that size and locate windows on the screen, display text with multiple fonts in a window, display images, and so on. 1.1 Introducing Swing When Java 1.0 was introduced, it contained a class library, which Sun called the Abstract Window Toolkit (AWT), for basic GUI programming. In theory, run on any of these platforms, with the “look-and-feel” of the target platform—hence Sun’s trademarked slogan: “Write Once, Run Anywhere.” Developers complained that they had to test their applications on each platform—a practice called “write once, debug everywhere.” In 1996, Netscape created a GUI library they called the IFC (Internet Foundation Classes) that used an entirely different approach. User interface elements, such as buttons, menus, and so on, were painted onto blank windows. Sun worked with Netscape to perfect this approach, creating a user interface library with the code name “Swing.” Swing was available as an extension to Java 1.1 and became a part of the standard library in Java SE 1.2. Swing is now the official name for the non-peer-based GUI toolkit. Swing is part of the Java Foundation Classes (JFC). Swing-based user interface elements will be somewhat slower to appear on the user’s screen than the peer- based components used by the AWT. On the other hand, the reasons to choose Swing are overwhelming: Swing has a rich and suitable set of user interface elements. Swing has few dependencies on the underlying platform; it is therefore less liable to platform-specific bugs. Swing gives a compatible user experience across platforms. Still, the third plus is also a potential drawback: If the user interface elements look the same on all platforms, they look different from the native controls, so users will be less familiar with them. 1.2 Creating a Frame A top-level window (that is, a window that is not contained inside another window) is called a frame in Java. The Abstract Window Toolkit (AWT) library has a class, called Frame, for this top level. The Swing version of this class is called JFrame and extends the Frame class. Thus, the decorations (buttons, title bar, icons, and so on) are drawn by the user’s windowing system, not by Swing. What is JFrame? JFrame is a class of javax.swing package extended by java.awt.frame, it adds support for JFC/SWING component architecture. It is the top level window, with border and a title bar. JFrame class has many methods which can be used to customize it. Creating a JFrame JFrame class has many constructors used to create a JFrame. Following is the description.  JFrame(): creates a frame which is invisible  JFrame(GraphicsConfiguration gc): creates a frame with a blank title and graphics configuration of screen device.  JFrame(String title): creates a JFrame with a title.  JFrame(String title, GraphicsConfiguration gc): creates a JFrame with specific Graphics configuration and specified title. Here is a simplest example just to create a JFrame. package Example; import java.awt.GraphicsConfiguration; import javax.swing.JFrame; public class JFrameExample { static GraphicsConfiguration gc; public static void main(String[] args){ JFrame frame= new JFrame(gc); frame.setVisible(true); } } Here is how it will display Change window size of a JFrame To resize a frame, JFrame provides a method JFrame.setSize(int width, int height), it takes two parameters width and height. Here is how code looks now package Example; import java.awt.GraphicsConfiguration; import javax.swing.JFrame; public class JFrameExample { static GraphicsConfiguration gc; public static void main(String[] args){ JFrame frame= new JFrame(gc); frame.setTitle("Welecome to Advance Java Programming"); frame.setSize(600, 400); frame.setVisible(true); } } Resize a JFrame After setting size of a JFrame you will notice still change it size by just simply putting the cursor at the corners and dragging it. Or if you press resize option next to close at the top right corner, it will maximize to the size of full screen. This happens because resize is set true by default. You can simply make false as JFrame.setResizable(false), now it will appear according to the dimensions you have given in code and will not resize by the graphical interface. Change position on the screen To change position of JFrame on screen JFrame provides a method JFrame.setlocation(int x, int y), it takes two paramters x represents position along x-axis and y represents position along y-axis. The top left corner of your screen is (0,0). Closing a JFrame You can easily close your JFrame by clicking on the X(cross) at the top left corner of JFrame. However JFrame.setDefaultCloseOperation(int) is a method provided by JFrame class, you can set the operation that will happen when user clicks on cross. If “0” is given as a parameter, JFrame will not close even after clicking on cross. The best practice is to use JFrame.EXIT_ON_CLOSE, it exits application (JFrame) and releases memory. JFrame.HIDE_ON_CLOSE: It does not close JFrame, simply hides it. JFrame.DISPOSE_ON_CLOSE: It dispose the frame off, but it keeps running and consumes memory. JFrame.DO_NOTHING_ON_CLOSE: It does nothing when user clicks on close. Here’s how the final code looks like package Example; import java.awt.GraphicsConfiguration; import javax.swing.JFrame; public class JFrameExample { static GraphicsConfiguration gc; public static void main(String[] args){ JFrame frame= new JFrame(gc); frame.setTitle("Welecome to Advance Java Programming"); frame.setSize(600, 400); frame.setLocation(200, 200); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setResizable(false); } } There are two technical issues that we need to address in every Swing program: First, all Swing components must be configured from the event dispatch thread, the thread of control that passes events such as mouse clicks and keystrokes to the user interface components. The following code fragment is used to execute statements in the event dispatch thread: EventQueue.invokeLater(() -> { statements }); Next, we define what should happen when the user closes the application’s frame. For this particular program, we want the program to exit. To select this behavior, we use the statement frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); In other programs with multiple frames, you would not want the program to exit just because the user closes one of the frames. By default, a frame is hidden when the user closes it, but the program does not terminate. 1.3 Positioning a Frame The JFrame class itself has only a few methods for changing how frames look. Here are some of the most important methods: The setLocation and setBounds methods for setting the position of the frame The setIconImage method, which tells the windowing system which icon to display in the title bar, task switcher window, and so on The setTitle method for changing the text in the title bar The setResizable method, which takes a boolean to determine if a frame will be resizeable by the user Figure 1.6 illustrates the inheritance hierarchy for the JFrame class. Figure 1.6 Inheritance hierarchy for the frame and component classes in AWT and Swing setLocation(x, y) where (0, 0) is the top left corner of the screen. Similarly, the setBounds method in Component lets you resize and relocate a component (in particular, a JFrame) in one step, as setBounds(x, y, width, height) Alternatively, you can give the windowing system control over window placement. If you call setLocationByPlatform(true); 1.3.1 Frame Properties Many methods of component classes come in getter/setter pairs, such as the following methods of the Frame class: public String getTitle() public void setTitle(String title) Such a getter/setter pair is called a property. For example, the following two methods define the locationByPlatform property: public boolean isLocationByPlatform() public void setLocationByPlatform(boolean b) 1.3.2 Determining a Good Frame Size To find out the screen size, use the following steps. Toolkit kit = Toolkit.getDefaultToolkit(); Dimension screenSize = kit.getScreenSize(); int screenWidth = screenSize.width; int screenHeight = screenSize.height; We use 50% of these values for the frame size, and tell the windowing system to position the frame: setSize(screenWidth / 2, screenHeight / 2); setLocationByPlatform(true); We also supply an icon. The ImageIcon class is convenient for loading images. Here is how you use it: Image img = new ImageIcon("icon.gif").getImage(); setIconImage(img); You can maximize a frame by calling frame.setExtendedState(Frame.MAXIMIZED_BOTH); Listing 1.2 sizedFrame/SizedFrameTest.java 1.4 Displaying Information in a Component In this section, we will show you how to display information inside a frame. For example, instead of displaying “Not a Hello World program” in text mode in a console window Figure 1.7 A frame that displays information When designing a frame, you add components into the content pane, using code such as the following: Container contentPane = frame.getContentPane(); Component c =...; contentPane.add(c);  Figure 1.8 Internal structure of a JFrame Up to Java Standard Edition (SE) 1.4, the add method of the JFrame class was defined to throw an exception with the message “Do not use JFrame.add(). Use JFrame.getContentPane().add() instead.” Thus, you can simply use the call frame.add(c); Here’s how to make a component onto which we can draw: class MyComponent extends JComponent { public void paintComponent(Graphics g) { code for drawing } } The paintComponent method takes one parameter of type Graphics. A Graphics object remembers a collection of settings for drawing images and text, such as the font you set or the current color. Displaying text is considered a special kind of drawing. The Graphics class has a drawString method that has the following syntax: g.drawString(text, x, y) In our case, we want to draw the string "Not a Hello World Program" in our original window, roughly one-quarter of the way across and halfway down. Thus, our paintComponent method looks like this: public class NotHelloWorldComponent extends JComponent { public static final int MESSAGE_X = 75; public static final int MESSAGE_Y = 100; public void paintComponent(Graphics g) { g.drawString("Not a Hello World program", MESSAGE_X, MESSAGE_Y); }... } Finally, a component should tell its users how big it would like to be. Override the getPreferredSize method and return an object of the Dimension class with the preferred width and height: public class NotHelloWorldComponent extends JComponent {  private static final int DEFAULT_WIDTH = 300; private static final int DEFAULT_HEIGHT = 200;... public Dimension getPreferredSize() { return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT); } } When you fill a frame with one or more components, and you simply want to use their preferred size, call the pack method instead of the setSize method: class NotHelloWorldFrame extends JFrame { public NotHelloWorldFrame() { add(new NotHelloWorldComponent()); pack(); } } 1.5 Working with 2D Shapes Starting with Java 1.0, the Graphics class has methods to draw lines, rectangles, ellipses, and so on. For example, you cannot vary the line thickness and cannot rotate the shapes. Java SE 1.2 introduced the Java 2D library, which implements a powerful set of graphical operations. To draw shapes in the Java 2D library, you need to obtain an object of the Graphics2D class. This class is a subclass of the Graphics class. Ever since Java SE 2, methods such as paintComponent automatically receive an object of the Graphics2D class. Simply use a cast, as follows: public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g;... } The Java 2D library organizes geometric shapes in an object-oriented fashion. Line2D Rectangle2D Ellipse2D These classes all implement the Shape interface. To draw a shape, you first create an object of a class that implements the Shape interface and then call the draw method of the Graphics2D class. For example: Rectangle2D rect =...; g2.draw(rect); Using the Java 2D shape classes introduces some complexity. For example, consider the following statement: float f = 1.2; // Error This statement does not compile because the constant 1.2 has type double, and the compiler is nervous about loss of precision. The remedy is to add an F suffix to the floating-point constant: float f = 1.2F; // Ok Now consider this statement: Rectangle2D r =... float f = r.getWidth(); // Error This statement does not compile either, for the same reason. The getWidth method returns a double. This time, the remedy is to provide a cast: float f = (float) r.getWidth(); // OK These suffixes and casts are a bit of a pain, so the designers of the 2D library decided to supply two versions of each shape class: Figure 10.9 shows the inheritance diagram. Figure 10.9 2D rectangle classes It is best to ignore the fact that the two concrete classes are static inner classes: When you construct both : Rectangle2D.Float floatRect = new Rectangle2D.Float(10.0F, 25.0F, 22.5F, 20.0F); Rectangle2D.Double doubleRect = new Rectangle2D.Double(10.0, 25.0, 22.5, 20.0); It is extend the common Rectangle2D class and the methods in the subclasses simply override those in the Rectangle2D superclass, You can simply use Rectangle2D variables to hold the rectangle references. Rectangle2D floatRect = new Rectangle2D.Float(10.0F, 25.0F, 22.5F, 20.0F); Rectangle2D doubleRect = new Rectangle2D.Double(10.0, 25.0, 22.5, 20.0); Furthermore, there is a Point2D class with subclasses Point2D.Float and Point2D.Double. Here is how to make a point object: Point2D p = new Point2D.Double(10, 20); The classes Rectangle2D and Ellipse2D both inherit from the common superclass RectangularShape. Admittedly, ellipses are not rectangular, but they have a bounding rectangle (see Figure 10.10). Figure 10.10 The bounding rectangle of an ellipse Rectangle2D and Ellipse2D objects are simple to construct. You need to specify The x and y coordinates of the top left corner; and The width and height. For ellipses, these refer to the bounding rectangle. For example, Ellipse2D e = new Ellipse2D.Double(150, 200, 100, 50); constructs an ellipse that is bounded by a rectangle with the top left corner at (150, 200), width of 100, and height of 50. You can’t simply construct a rectangle as Rectangle2D rect = new Rectangle2D.Double(px, py, qx - px, qy - py); // Error In that case, first create a blank rectangle and use the setFrameFromDiagonal method, as follows: Rectangle2D rect = new Rectangle2D.Double(); rect.setFrameFromDiagonal(px, py, qx, qy); Or, even better, if you have the corner points as Point2D objects p and q, use Figure 10.11 Relationships between the shape classes rect.setFrameFromDiagonal(p, q); When constructing an ellipse, you usually know the center, width, and height, but not the corner points of the bounding rectangle (which don’t even lie on the ellipse). The setFrameFromCenter method uses the center point, but it still requires one of the four corner points. Thus, you will usually end up constructing an ellipse as follows: Ellipse2D ellipse = new Ellipse2D.Double(centerX - width / 2, centerY - height / 2, width, height); To construct a line, you supply the start and end points, either as Point2D objects or as pairs of numbers: Line2D line = new Line2D.Double(start, end); or Line2D line = new Line2D.Double(startX, startY, endX, endY); The program in Listing 10.4 draws a rectangle, the ellipse that is enclosed in the rectangle, a diagonal of the rectangle, and a circle that has the same center as the rectangle. Figure 10.12 shows the result.  Figure 10.12 Drawing geometric shapes (Page.566) 1.6 Using Color (page. 569) The setPaint method of the Graphics2D class lets you select a color that is used for all subsequent drawing operations on the graphics context. For example: g2.setPaint(Color.RED); g2.drawString("Warning!", 100, 100); You can fill the interiors of closed shapes (such as rectangles or ellipses) with a color. Simply call fill instead of draw: Rectangle2D rect =...; g2.setPaint(Color.RED); g2.fill(rect); // fills rect with red Define colors with the Color class. The java.awt.Color class offers predefined constants for the following 13 standard colors: BLACK, BLUE, CYAN, DARK_GRAY, GRAY, GREEN, LIGHT_GRAY, MAGENTA, ORANGE, PINK, RED, WHITE, YELLOW Using a scale of 0–255 (that is, one byte) for the redness, blueness, and greenness, call the Color constructor like this: Color(int redness, int greenness, int blueness) Here is an example of setting a custom color: g2.setPaint(new Color(0, 128, 128)); // a dull blue-green g2.drawString("Welcome!", 75, 125); To set the background color, use the setBackground method of the Component class, an ancestor of JComponent. MyComponent p = new MyComponent(); p.setBackground(Color.PINK); There is also a setForeground method. It specifies the default color that is used for drawing on the component.  p.setBackground(SystemColor.window) //default color of window Table 10.1 lists the system color names and their meanings. 10.7 Using Special Fonts for Text To find out which fonts are available on a particular computer, call the getAvailableFontFamilyNames method of the GraphicsEnvironment class. The method returns an array of strings containing the names of all available fonts. To obtain an instance of the GraphicsEnvironment class that describes the graphics environment of the user’s system, use the static getLocalGraphicsEnvironment method. The following program prints the names of all fonts on your system: On one system, the list starts out like this: Abadi MT Condensed Light Arial Arial Black Arial Narrow Arioso Baskerville Binner Gothic... and goes on for another seventy or so fonts. Font face names can be trademarked, and font designs can be copyrighted in some jurisdictions. To draw characters in a font, you must first create an object of the class Font. Specify the font face name, the font style, and the point size. Here is an example of how you construct a Font object: Font sansbold14 = new Font("SansSerif", Font.BOLD, 14); Specify the style (plain, bold, italic, or bold italic) by setting the second Font constructor argument to one of the following values: Font.PLAIN Font.BOLD Font.ITALIC Font.BOLD + Font.ITALIC You can read font files in TrueType, OpenType, or PostScript Type 1 formats. You need an input stream for the font—typically from a file or URL. Then, call the static Font.createFont method: URL url = new URL("http://www.fonts.com/Wingbats.ttf"); InputStream in = url.openStream(); Font f1 = Font.createFont(Font.TRUETYPE_FONT, in); The font is plain with a font size of 1 point. Use the deriveFont method to get a font of the desired size: Font f = f1.deriveFont(14.0F); The Java fonts contain the usual ASCII characters as well as symbols. For example, if you print the character '\u2297' in the Dialog font, you get a (x) character. Here’s the code that displays the string “Hello, World!” in the standard sans serif font on your system, using 14-point bold type: Font sansbold14 = new Font("SansSerif", Font.BOLD, 14); g2.setFont(sansbold14); String message = "Hello, World!"; g2.drawString(message, 75, 100); We need to know the width and height of the string in pixels. These dimensions depend on three factors: The font used (in our case, sans serif, bold, 14 point); The string (in our case, “Hello, World!”); and The device on which the font is drawn (in our case, the user’s screen). To obtain an object that represents the font characteristics of the screen device, call the getFontRenderContext method of the Graphics2D class. It returns an object of the FontRenderContext class. Simply pass that object to the getStringBounds method of the Font class: FontRenderContext context = g2.getFontRenderContext(); Rectangle2D bounds = sansbold14..getStringBounds(message, context); The getStringBounds method returns a rectangle that encloses the string. Figure 10.13 Typesetting terms illustrated Thus, you can obtain string width, height, and ascent as follows: double stringWidth = bounds.getWidth(); double stringHeight = bounds.getHeight(); double ascent = -bounds.getY(); If you need to know the descent or leading, use the getLineMetrics method of the Font class. LineMetrics metrics = f.getLineMetrics(message, context); float descent = metrics.getDescent(); float leading = metrics.getLeading(); The following code uses all this information to center a string in its surrounding component: FontRenderContext context = g2.getFontRenderContext(); Rectangle2D bounds = f.getStringBounds(message, context); // (x,y) = top left corner of text double x = (getWidth() - bounds.getWidth()) / 2; double y = (getHeight() - bounds.getHeight()) / 2; // add ascent to y to reach the baseline double ascent = -bounds.getY(); double baseY = y + ascent; g2.drawString(message, (int) x, (int) baseY); To show that the positioning is accurate, the sample program also draws the baseline and the bounding rectangle. Figure 1.14 shows the screen display; Figure 1.14 Drawing the baseline and string bounds 1.8 Displaying Images Once images are stored in local files or someplace on the Internet, you can read them into a Java application and display them on Graphics objects. There are many ways of reading images. Here, we use the ImageIcon class that you already saw: Image image = new ImageIcon(filename).getImage(); Now the variable image contains a reference to an object that encapsulates the image data. You can display the image with the drawImage method of the Graphics class. public void paintComponent(Graphics g) {... g.drawImage(image, x, y, null); } Listing 10.6 takes this a little bit further and tiles the window with the graphics image. The result looks like the screen shown in Figure 10.15. We do the tiling in the paintComponent method. We first draw one copy of the image in the top left corner and then use the copyArea call to copy it into the entire window:  for (int i = 0; i * imageWidth { JFrame frame = new ButtonFrame(); frame.setTitle("Buttom Frame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); }); } } Java adapter classes provide the default implementation of listener interfaces. java.awt.event Adapter classes Adapter class Listener interface WindowAdapter WindowListener KeyAdapter KeyListener MouseAdapter MouseListener MouseMotionAdapter MouseMotionListener FocusAdapter FocusListener ComponentAdapter ComponentListener ContainerAdapter ContainerListener Java WindowAdapter Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class AdapterExample{ 4. Frame f; 5. AdapterExample(){ 6. f=new Frame("Window Adapter"); 7. f.addWindowListener(new WindowAdapter(){ 8. public void windowClosing(WindowEvent e) { 9. f.dispose(); 10. } 11. }); 12. 13. f.setSize(400,400); 14. f.setLayout(null); 15. f.setVisible(true); 16. } 17. public static void main(String[] args) { 18. new AdapterExample(); 19. } 20. } Java MouseAdapter Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class MouseAdapterExample extends MouseAdapter{ 4. Frame f; 5. MouseAdapterExample(){ 6. f=new Frame("Mouse Adapter"); 7. f.addMouseListener(this); 8. 9. f.setSize(300,300); 10. f.setLayout(null); 11. f.setVisible(true); 12. } 13. public void mouseClicked(MouseEvent e) { 14. Graphics g=f.getGraphics(); 15. g.setColor(Color.BLUE); 16. g.fillOval(e.getX(),e.getY(),30,30); 17. } 18. 19. public static void main(String[] args) { 20. new MouseAdapterExample(); 21. } 22. } Java MouseMotionAdapter Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class MouseMotionAdapterExample extends MouseMotionAdapter{ 4. Frame f; 5. MouseMotionAdapterExample(){ 6. f=new Frame("Mouse Motion Adapter"); 7. f.addMouseMotionListener(this); 8. 9. f.setSize(300,300); 10. f.setLayout(null); 11. f.setVisible(true); 12. } 13. public void mouseDragged(MouseEvent e) { 14. Graphics g=f.getGraphics(); 15. g.setColor(Color.ORANGE); 16. g.fillOval(e.getX(),e.getY(),20,20); 17. } 18. public static void main(String[] args) { 19. new MouseMotionAdapterExample(); 20. } 21. } Java KeyAdapter Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class KeyAdapterExample extends KeyAdapter{ 4. Label l; 5. TextArea area; 6. Frame f; 7. KeyAdapterExample(){ 8. f=new Frame("Key Adapter"); 9. l=new Label(); 10. l.setBounds(20,50,200,20); 11. area=new TextArea(); 12. area.setBounds(20,80,300, 300); 13. area.addKeyListener(this); 14. 15. f.add(l);f.add(area); 16. f.setSize(400,400); 17. f.setLayout(null); 18. f.setVisible(true); 19. } 20. public void keyReleased(KeyEvent e) { 21. String text=area.getText();  22. String words[]=text.split("\\s"); 23. l.setText("Words: "+words.length+" Characters:"+text.length()); 24. } 25. 26. public static void main(String[] args) { 27. new KeyAdapterExample(); 28. } 29. } 1.1.c Swing and the Model-View-Controller Design Pattern At first we discuss the concept of design patterns and then look at the “model-view-controller” pattern that has greatly influenced the design of the Swing framework. 1.1.1 Design Patterns When solving a problem, you don’t usually figure out a solution from first principles. Instead, you are likely to be guided by your past experience, or you may ask other experts for advice on what has worked for them. Design patterns are a method for presenting this expertise in a structured way. 1.1.2 The Model-View-Controller Pattern A user interface component such as a button, a checkbox, a text field, or a sophisticated tree control. Every component has three characteristics: Its content, such as the state of a button (pushed in or not), or the text in a text field Its visual appearance (color, size, and so on) Its behavior (reaction to events) Obviously, the visual appearance of a button depends on the look-and-feel. To do this, the Swing designers turned to a well-known design pattern: the model- view- controller pattern. The model-viewcontroller (MVC) design pattern teaches how to accomplish this. Implement three separate classes: The model, which stores the content The view, which displays the content The controller, which handles user input Figure. Model and view of a text field For example, an HTML editor can offer two simultaneous views of the same content: a WYSIWYG view and a “raw tag” view. The controller handles the user-input events, such as mouse clicks and keystrokes. It then decides whether to translate these events into changes in the model or the view. What You See Is What You Get Figure. Two separate views of the same model Figure. Interactions among model, view, and controller objects 1.1.3 A Model-View-Controller Analysis of Swing Buttons Still, buttons are about the simplest user interface elements, so they are a good place to get comfortable with the model-view-controller pattern. We will encounter similar kinds of classes and interfaces for the more sophisticated Swing components. For most components, the model class implements an interface whose name ends in Model; in this case, the interface is called ButtonModel. Swing library contains a single class, called DefaultButtonModel, that implements this interface. The Sort of data maintained by a button model by looking at the properties of the ButtonModel interface—see Table 1.1. Table 1.1 Properties of the ButtonModel Interface Each JButton object stores a button model object which you can retrieve. JButton button = new JButton("Blue"); ButtonModel model = button.getModel(); 1.2 Introduction to Layout Management In general, components are placed inside containers, and a layout manager determines the positions and sizes of components in a container. Buttons, text fields, and other user interface elements extend the class Component. Components can be placed inside containers, such as panels. Containers can themselves be put inside other containers, so the class Container extends Component. Figure 1.8 shows the inheritance hierarchy for Component. Each container has a default layout manager, but we can always set our own. For example, the statement uses the GridLayout class to lay out the components in four rows and four columns. panel.setLayout(new GridLayout(4, 4)); 1.2.1 Border Layout The border layout manager is the default layout manager of the content pane of every JFrame. We can choose to place the component in the center, north, south, east, or west of the content pane (see Figure 1.9). Figure 1.9 Border layout For example: frame.add(component, BorderLayout.SOUTH); If we don’t supply any value, CENTER is assumed. Unlike the flow layout, the border layout grows all components to fill the available space. (The flow layout leaves each component at its preferred size.) This is a problem when you add a button: frame.add(yellowButton, BorderLayout.SOUTH); // don't Figure 1.10 A single button managed by a border layout To solve this problem, use additional panels. For example, look at Figure 1.11. The three buttons at the bottom of the screen are all contained in a panel. The panel is put into the southern region of the content pane.  Figure 1.11 Panel placed at the southern region of the frame To achieve this configuration, first create a new JPanel object, then add the individual buttons to the panel. Finally, add the panel to the content pane of the frame. JPanel panel = new JPanel(); panel.add(yellowButton); panel.add(blueButton); panel.add(redButton); frame.add(panel, BorderLayout.SOUTH); 1.2.2 Grid Layout The grid layout arranges all components in rows and columns like a spreadsheet. All components are given the same size. The calculator program in Figure 1.12 Figure 1.12 A calculator In the constructor of the grid layout object, you specify how many rows and columns you need. panel.setLayout(new GridLayout(4, 4)); Add the components, starting with the first entry in the first row, then the second entry in the first row, and so on. panel.add(new JButton("1")); panel.add(new JButton("2")); Listing 12.1 calculator/CalculatorPanel.java Page: 109 12.3 Text Input You can use the JTextField and JTextArea components for text input. A text field can accept only one line of text; a text area can accept multiple lines of text. AJPasswordField accepts one line of text without showing the contents. All three of these classes inherit from a class called JTextComponent. 12.3.1 Text Fields The usual way to add a text field to a window is to add it to a panel or other container—just as we would add a button: JPanel panel = new JPanel(); JTextField textField = new JTextField("Default input", 20); panel.add(textField); This code adds a text field and initializes it by placing the string "Default input" inside it. The second parameter of this constructor sets the width. In this case, the width is 20 “columns.” To make a blank text field, just leave out the string as a parameter for the JTextField constructor: JTextField textField = new JTextField(20); textField.setText("Hello!"); String text = textField.getText().trim(); To change the font in which the user text appears, use the setFont method. 12.3.2 Labels and Labeling Components Labels are components that hold text. You can use a label to identify components. To label a component that does not itself come with an identifier: 1. Construct a JLabel component with the correct text. 2. Place it close enough to the component you want to identify so that the user can see that the label identifies the correct component. That interface defines a number of useful constants such as LEFT, RIGHT, CENTER, NORTH, EAST, and so on. The JLabel class is one of several Swing classes that implement this interface. Therefore, you can specify a right-aligned label either as JLabel label = new JLabel("User name: ", SwingConstants.RIGHT); or JLabel label = new JLabel("User name: ", JLabel.RIGHT); The setText and setIcon methods let you set the text and icon of the label at runtime. 12.3.3 Password Fields Password fields are a special kind of text field. Each typed character is represented by an echo character, typically an asterisk (*).Swing supplies a JPasswordField class that implements such a text field. 12.3.4 Text Areas  textArea = new JTextArea(8, 40); // 8 lines of 40 columns each textArea.setLineWrap(true); // long lines are wrapped 12.3.5 Scroll Panes In Swing, a text area does not have scrollbars. If you want scrollbars, you have to place the text area inside a scroll pane. textArea = new JTextArea(8, 40); JScrollPane scrollPane = new JScrollPane(textArea); 12.4 Choice Components 12.4.1 Checkboxes: If you want to collect just a “yes” or “no” input, use a checkbox component. Checkboxes need a label next to them to identify their purpose. Give the label text in the constructor: bold = new JCheckBox("Bold"); Use the setSelected method to turn a checkbox on or off. For example: bold.setSelected(true); The isSelected method then retrieves the current state of each checkbox. It is false if unchecked, true if checked. In our program, the two checkboxes share the same action listener. ActionListener listener =... bold.addActionListener(listener); italic.addActionListener(listener); The listener queries the state of the bold and italic checkboxes and sets the font of the panel to plain, bold, italic, or both bold and italic. ActionListener listener = event -> { int mode = 0; if (bold.isSelected()) mode += Font.BOLD; if (italic.isSelected()) mode += Font.ITALIC; label.setFont(new Font(Font.SERIF, mode, FONTSIZE)); }; 12.4.2 Radio Buttons In many cases, we want the user to check only one of several boxes. When another box is checked, the previous box is automatically unchecked. Such a group of boxes is often called a radio button group because the buttons work like the station selector buttons on a radio. When you push in one button, the previously depressed button pops out. The button group object is reponsible for turning off the previously set button when a new button is clicked. ButtonGroup group = new ButtonGroup(); JRadioButton smallButton = new JRadioButton("Small", false); group.add(smallButton); JRadioButton mediumButton = new JRadioButton("Medium", true); group.add(mediumButton); In our example program, we define an action listener that sets the font size to a particular value: ActionListener listener = event -> label.setFont(new Font("Serif", Font.PLAIN, size)); We could have a single listener that computes the size as follows: if (smallButton.isSelected()) size = 8; else if (mediumButton.isSelected()) size = 12;... However, we prefer to use separate action listener objects because they tie the size values more closely to the buttons. 12.4.3 Borders If we have multiple groups of radio buttons in a window, We want to visually indicate which buttons are grouped. Swing provides a set of useful borders for this purpose. We can apply a border to any component that extends JComponent. We can choose from quite a few borders, but We need to follow the same steps for all of them. 1. Call a static method of the BorderFactory to create a border. We can choose among the following styles (see Figure 12.16): Lowered bevel Raised bevel Etched Line Matte Empty (just to create some blank space around the component) 2. If We like, add a title to your border by passing your border to BorderFactory.createTitledBorder. 3. If We really want to go all out, combine several borders with a call to BorderFactory.createCompoundBorder. 4. Add the resulting border to our component by calling the setBorder method of the JComponent class. For example, here is how you add an etched border with a title to a panel: Border etched = BorderFactory.createEtchedBorder(); Border titled = BorderFactory.createTitledBorder(etched, "A Title"); panel.setBorder(titled); 12.4.4 Combo Boxes If you have more than a handful of alternatives, radio buttons are not a good choice because they take up too much screen space. Instead, you can use a combo box. When the user clicks on this component, a list of choices drops down, and the user can then select one of them (see Figure 12.17). If the drop-down list box is set to be editable, you can edit the current selection as if it were a text field. For that reason, this component is called a combo box. As of Java SE 7, the JComboBox class is a generic class. For example, a JComboBox holds objects of type String, and a JComboBox holds integers. Call the setEditable method to make the combo box editable. Note that editing affects only the selected item. It does not change the list of choices in any way. If your combo box isn’t editable, you are better off calling combo.getItemAt(combo.getSelectedIndex()) which gives you the selected item with the correct type. In the example program, the user can choose a font style from a list of styles (Serif, SansSerif, Monospaced, etc.). The user can also type in another font. Add the choice items with the addItem method. In our program, addItem is called only in the constructor, but you can call it any time. JComboBox faceCombo = new JComboBox(); faceCombo.addItem("Serif"); faceCombo.addItem("SansSerif");... This method adds the string to the end of the list. You can add new items anywhere in the list with the insertItemAt method: faceCombo.insertItemAt("Monospaced", 0); // add at the beginning If you need to remove items at runtime, use the removeItem or removeItemAt method, depending on whether you supply the item to be removed or its position. faceCombo.removeItem("Monospaced"); faceCombo.removeItemAt(0); // remove first item The removeAllItems method removes all items at once. ActionListener listener = event -> label.setFont(new Font( faceCombo.getItemAt(faceCombo.setSelectedIndex()), Font.PLAIN, DEFAULT_SIZE)); 12.4.5 Sliders Sliders offer a choice from a continuum of values—for example, any number between 1 and 100. The most common way of constructing a slider is as follows: JSlider slider = new JSlider(min, max, initialValue); If we omit the minimum, maximum, and initial values, they are initialized with 0, 100, and 50, respectively. Or if we want the slider to be vertical, use the following constructor call: JSlider slider = new JSlider(SwingConstants.VERTICAL, min, max, initialValue); These constructors create a plain slider, such as the top slider in Figure 12.18. You will see presently how to add decorations to a slider. ChangeListener listener = event -> { JSlider slider = (JSlider) event.getSource(); int value = slider.getValue();... }; For example, in the sample program, the second slider uses the following settings: slider.setMajorTickSpacing(20); slider.setMinorTickSpacing(5); These instructions only set the units for the tick marks. To actually have the tick marks appear, call slider.setPaintTicks(true); we can force the slider to snap to ticks. slider.setSnapToTicks(true); We can display tick mark labels for the major tick marks by calling slider.setPaintLabels(true); We need to fill a hash table with keys of type Integer and values of type Component. Hashtable labelTable = new Hashtable(); labelTable.put(0, new JLabel("A")); labelTable.put(20, new JLabel("B"));... labelTable.put(100, new JLabel("F")); slider.setLabelTable(labelTable); The fourth slider in Figure 12.18 has no track. To suppress the “track” in which the slider moves, call slider.setPaintTrack(false); The fifth slider has its direction reversed by a call to slider.setInverted(true); 12.5 Menus: 12.5 Menus 12.5.1 Menu Building 12.5.2 Icons in Menu Items 12.5.3 Checkbox and Radio Button Menu Items 12.5.4 Pop-Up Menus 12.5.5 Keyboard Mnemonics and Accelerators 12.5.6 Enabling and Disabling Menu Items 12.5.7 Toolbars 12.5.8 Tooltips Swing also supports another type of user interface element—pull-down menus that are familiar from GUI applications. A menu bar at the top of a window contains the names of the pull-down menus. Clicking on a name opens the menu containing menu items and submenus. When the user clicks on a menu item, all menus are closed and a message is sent to the program. Figure 12.19 shows a typical menu with a submenu. 12.5.1 Menu Building Building menus is straightforward. First, create a menu bar: JMenuBar menuBar = new JMenuBar(); Normally, We want it to appear at the top of a frame. We can add it there with the setJMenuBar method:  frame.setJMenuBar(menuBar); For each menu, We create a menu object: JMenu editMenu = new JMenu("Edit"); Add the top-level menus to the menu bar: menuBar.add(editMenu); Add menu items, separators, and submenus to the menu object: JMenuItem pasteItem = new JMenuItem("Paste"); editMenu.add(pasteItem); editMenu.addSeparator(); JMenu optionsMenu =...; // a submenu editMenu.add(optionsMenu); When the user selects a menu, an action event is triggered. we need to install an action listener for each menu item: ActionListener listener =...; pasteItem.addActionListener(listener); The method JMenu.add(String s) conveniently adds a menu item to the end of a menu. For example: editMenu.add("Paste"); The add method returns the created menu item, so you can capture it and add the listener, as follows: JMenuItem pasteItem = editMenu.add("Paste"); pasteItem.addActionListener(listener); We can define a class that implements the Action interface, usually by extending the AbstractAction convenience class, specify the menu item label in the constructor of the AbstractAction object, and override the actionPerformed method to hold the menu action handler. For example: Action exitAction = new AbstractAction("Exit") // menu item text goes here { public void actionPerformed(ActionEvent event) { // action code goes here System.exit(0); } }; You can then add the action to the menu: JMenuItem exitItem = fileMenu.add(exitAction); This is just a convenient shortcut for JMenuItem exitItem = new JMenuItem(exitAction); fileMenu.add(exitItem); 12.5.2 Icons in Menu Items Menu items are very similar to buttons. In fact, the JMenuItem class extends the AbstractButton class. We can specify the icon with the JMenuItem(String, Icon) or JMenuItem(Icon) constructor, or We can set it with the setIcon method that the JMenuItem class inherits from the AbstractButton class. Here is an example: JMenuItem cutItem = new JMenuItem("Cut", new ImageIcon("cut.gif")); cutItem.setHorizontalTextPosition(SwingConstants.LEFT); moves the menu item text to the left of the icon. We can also add an icon to an action:  cutAction.putValue(Action.SMALL_ICON, new ImageIcon("cut.gif")); Alternatively, We can set the icon in the AbstractAction constructor: cutAction = new AbstractAction("Cut", new ImageIcon("cut.gif")) { public void actionPerformed(ActionEvent event) {... } }; 12.5.3 Checkbox and Radio Button Menu Items Apart from the button decoration, treat these menu items just as We would any others. For example, here is how We create a checkbox menu item: JCheckBoxMenuItem readonlyItem = new JCheckBoxMenuItem("Read-only"); optionsMenu.add(readonlyItem); The radio button menu items work just like regular radio buttons. We must add them to a button group. When one of the buttons in a group is selected, all others are automatically deselected. ButtonGroup group = new ButtonGroup(); JRadioButtonMenuItem insertItem = new JRadioButtonMenuItem("Insert"); insertItem.setSelected(true); JRadioButtonMenuItem overtypeItem = new JRadioButtonMenuItem("Overtype"); group.add(insertItem); group.add(overtypeItem); optionsMenu.add(insertItem); optionsMenu.add(overtypeItem); 12.5.4 Pop-Up Menus Apop-up menu is a menu that is not attached to a menu bar but floats somewhere. Create a pop-up menu just as you create a regular menu, except that a pop-up menu has no title. JPopupMenu popup = new JPopupMenu(); Then, add your menu items as usual: JMenuItem item = new JMenuItem("Cut"); item.addActionListener(listener); popup.add(item); For example: popup.show(panel, x, y); Usually, you want to pop up a menu when the user clicks a particular mouse button—the so-called pop-up trigger. To pop up a menu when the user clicks on a component, using the pop-up trigger, simply call the method component.setComponentPopupMenu(popup); The child component can inherit the parent component’s pop-up menu by calling child.setInheritsPopupMenu(true); 12.5.5 Keyboard Mnemonics and Accelerators It is a real convenience for the experienced user to select menu items by keyboard mnemonics. We can create a keyboard mnemonic for a menu item by specifying a mnemonic letter in the menu item constructor: JMenuItem aboutItem = new JMenuItem("About", 'A'); For example, if We have a mnemonic “A” for the menu item “Save As,” then it makes more sense to underline the second “A” (Save As). We can specify which character you want to have underlined by calling the setDisplayedMnemonicIndex method. If We have an Action object, We can add the mnemonic as the value of the Action.MNEMONIC_KEY key, as follows: cutAction.putValue(Action.MNEMONIC_KEY, new Integer('A')); To attach a mnemonic to a menu, call the setMnemonic method: JMenu helpMenu = new JMenu("Help"); helpMenu.setMnemonic('H'); For example, the following call attaches the accelerator Ctrl+O to the openItem menu item: openItem.setAccelerator(KeyStroke.getKeyStroke("ctrl O")); 12.5.6 Enabling and Disabling Menu Items Occasionally, a particular menu item should be selected only in certain contexts. For example, when a document is opened in read-only mode, the Save menu item is not meaningful. A deactivated menu item is shown in gray, and it cannot be selected (see Figure 12.23). To enable or disable a menu item, use the setEnabled method: saveItem.setEnabled(false); There are two strategies for enabling and disabling menu items. the Save and Save As menu items and disable them. Alternatively, We can disable items just before displaying the menu. To do this, you must register a listener for the “menu selected” event. The javax.swing.event package defines a MenuListener interface with three methods: void menuSelected(MenuEvent event) void menuDeselected(MenuEvent event) void menuCanceled(MenuEvent event) The menuSelected method is called before the menu is displayed. The following code shows how to disable the Save and Save As actions whenever the Read Only checkbox menu item is selected: public void menuSelected(MenuEvent event) { saveAction.setEnabled(!readonlyItem.isSelected()); saveAsAction.setEnabled(!readonlyItem.isSelected()); } 12.5.7 Toolbars A toolbar is a button bar that gives quick access to the most commonly used commands in a program (see Figure 12.24) Toolbars are straightforward to program. Add components into the toolbar: JToolBar bar = new JToolBar(); bar.add(blueButton); The JToolBar class also has a method to add an Action object. Simply populate the toolbar with Action objects, like this: bar.add(blueAction); We can separate groups of buttons with a separator: bar.addSeparator(); Then, add the toolbar to the frame: add(bar, BorderLayout.NORTH); We can also specify a title for the toolbar that appears when the toolbar is undocked: bar = new JToolBar(titleString); By default, toolbars are initially horizontal. To have a toolbar start out vertical, use bar = new JToolBar(SwingConstants.VERTICAL) or bar = new JToolBar(titleString, SwingConstants.VERTICAL) 12.5.8 Tooltips A disadvantage of toolbars is that users are often mystified by the meanings of the tiny icons in toolbars. To solve this problem, user interface designers invented tooltips. In Swing, you can add tooltips to any JComponent simply by calling the setToolTipText method: exitButton.setToolTipText("Exit"); Alternatively, if you use Action objects, you associate the tooltip with the SHORT_DESCRIPTION key: exitAction.putValue(Action.SHORT_DESCRIPTION, "Exit"); 11.3 Text Input 11.3.1 Text Fields 11.3.2 Labels and Labeling Components 11.3.3 Password Fields 11.3.4 Text Areas 11.3.5 Scroll Panes 11.4 Choice Components 11.4.1 Checkboxes 11.4.2 Radio Buttons 11.4.3 Borders 11.4.4 Combo Boxes 11.4.5 Sliders 11.5 Menus 11.5.1 Menu Building 11.5.2 Icons in Menu Items 11.5.3 Checkbox and Radio Button Menu Items 11.5.4 Pop-Up Menus 11.5.5 Keyboard Mnemonics and Accelerators 11.5.6 Enabling and Disabling Menu Items 11.5.7 Toolbars 11.5.8 Tooltips