CS 240 Week 9

1. CS 240Week 9

2. EventQueue.invokeLater • In Swing, all user interface operations must occur on the “UI thread” • All components should be created on the UI thread • All method calls on UI components should happen on the UI thread • EventQueue.invokeLater runs the specified code on the UI thread • The main method for Swing programs should call EventQueue.invokeLater to create the UI • The main thread exits immediately after calling EventQueue.invokeLater, but the UI thread keeps the program running • EXAMPLE: EmptyFrame

3. JFrame • Use JFrame class to create top-level windows • setTitle method sets the window’s title • setDefaultCloseOperation method specifies what should happen when the user clicks the window’s close icon • setLocation method sets the window’s location on the desktop • setVisible method shows or hides the window • setSize method sets the window’s size • EXAMPLE: EmptyFrame

4. JFrame • add method adds a new subcomponent to the window • pack method sets the window’s size according to the preferred size and layout of the window’s subcomponents • EXAMPLE: SimpleFrame

5. JComponent • User interface components are subclasses of JComponent that provide custom drawing and event handling functionality • getSize and setSize methods get and set component’s width and height • getWidth and getHeight methods return component’s width and height individually • setBackground method is used to set the component’s background color • setPreferredSize, setMinimumSize, setMaximumSize methods are used to express the components preferred, min, and max sizes • paintComponent method draws the contents of the component • Graphics2D class is used to perform drawing operations in a component • EXAMPLE: Drawing

6. Drawing • Color • Red, Green, Blue, Alpha (transparency) components • new Color(210, 180, 140, 192) • Graphics.setColor method sets the current drawing color • Drawing origin is the component’s top-left corner. X values increase as you move right. Y values increase as you move down. • Representing points • Point2D superclass • Point2D.Float and Point2D.Double subclasses (nested inside Point2D) • Point2D.Double pt = new Point2D.Double(x, y)

7. Drawing Rectangles • Rectangles • Graphics.drawRect(x, y, width, height) • Graphics.fillRect(x, y, width, height) • OR • Rectangle2D superclass • Rectangle2D.Float and Rectangle2D.Double subclasses (nested inside Rectangle2D) • Rectangle2D rect = new Rectangle2D.Double(x, y, w, h) • Graphics2D.draw(rect) • Graphics2D.fill(rect) • EXAMPLE: Drawing

8. Drawing Ellipses • Ellipses • Graphics.drawOval(x, y, width, height) • Graphics.fillOval(x, y, width, height) • OR • Ellipse2D superclass • Ellipse2D.Float and Ellipse2D.Double subclasses (nested inside Ellipse2D) • Ellipse2D ellipse = new Ellipse2D.Double(x, y, w, h) • Graphics2D.draw(ellipse) • Graphics2D.fill(ellipse)

9. Drawing Lines • Lines • Graphics.drawLine(x, y, width, height) • OR • Line2D superclass • Line2D.Float and Line2D.Double subclasses (nested inside Line2D) • Line2D line = new Line2D.Double(x1, y1, x2, y2) • Graphics2D.setStroke method sets the line thickness and style • g2d.setStroke(new BasicStroke(5)); // line 5 pixels wide • Graphics2D.draw(line) • EXAMPLE: Drawing

10. Drawing Text • Font class represents fonts • Font font = new Font(name, style, size) • Font font = new Font(“SansSerif”, Font.PLAIN, 72); • Graphics.setFont method sets the current font • g2d.setFont(font); • Graphics2D.drawString(string, x, y) • (x, y) is location of text’s baseline • g2d.drawString(“Hi There”, 100, 200); • EXAMPLE: Drawing

11. Drawing Text • Calculating text metrics (width, height, etc.) • FontRenderContext context = g2d.getFontRenderContext(); • Rectangle2D bounds = font.getStringBounds(message, context); • double stringWidth = bounds.getWidth(); • doublestringHeight = bounds.getHeight(); • double ascent = -bounds.getY(); • If you need descent and leading • LineMetrics metrics = font.getLineMetrics(message, context); • float descent = metrics.getDescent(); • float leading = metrics.getLeading();

12. Drawing Images • The BufferedImage class can be used to store and manipulate images in memory. You can: • Load an existing image into a BufferedImage • Modify an image by changing the pixel values in a BufferedImage • Create a new image by creating an empty BufferedImage and modifying its pixel values • Save a BufferedImage to a file

13. Drawing Images • The ImageIO class can be used to load images from disk or the web, and to save images to disk • Load image from disk: • String filename = "..."; • Imageimage = ImageIO.read(new File(filename)); • EXAMPLE: Drawing • Load image from URL: • String urlname = "..."; • Imageimage = ImageIO.read(new URL(urlname));

14. Drawing Images • Graphics.drawImage(image, destX1, destY1, destX2, destY2, srcX1, srcY1, srcX2, srcY2) • “dest” is the destination rectangle where the image should be drawn in the component • “src” is the source rectangle in the image to be drawn • Can be only part of the image • “dest” and “src” do not have to be the same size. The drawImage method will scale the source image to fit in the destination rectangle. • This is one way to scale an image • EXAMPLE: Drawing

15. Event Handling • User actions are called “events” • Low-level window events • Window changes • Low-level component events • Mouse events, Keyboard events, Component changes • High-level component-specific events • Button events, Menu events, List events, etc. • Events are handled by attaching “event listeners” to windows and components • Swing defines a “listener interface” for each category of events • Examples: WindowListener, MouseListener, MenuListener

16. Event Handling • A “listener” is an object that implements a listener interface • Listeners are attached to windows and components by calling the appropriate “addXXXListener” methods • addWindowListener, addMouseListener, addMenuListener, etc. • The window or component will notify all attached listeners about all relevant events • windowActivated, mouseClicked, menuSelected, etc. • Listener methods accept an EventObject parameter that describes the event that occurred • WindowEvent, MouseEvent, MenuEvent, etc. • The EventObject.getSourcemethod returns the window or component that generated the event

17. Event Handling • Listeners are typically implemented as inner classes • Named inner class • class MyMouseHandler implements MouseListener { … } • this.addMouseListener(new MyMouseHandler()); • Anonymous inner class • this.addMouseListener(new MouseListener() { … });

18. Event Handling • Event Adapter classes • Frequently, a program only wants to handle a few of the events defined by a listener interface • However, implementing the listener interface requires implementations for all event methods • Swing provides Adapter superclasses that provide empty implementations of all methods in a listener interface • WindowAdapter, MouseAdapter, KeyAdapter, etc. • This allows a program to create a listener by subclassing an adapter class, and overriding only the event methods it cares about • Some adapter classes implement multiple listener interfaces • EXAMPLE: MouseAdapter implements MouseListener, MouseMotionListener, and MouseWheelListener

19. Mouse Events • MouseListener interface • MouseMotionListener interface • MouseWheelListener interface • MouseAdapter class • EXAMPLE: Dragging and scrolling shapes in Drawing

20. Component Events • ComponentListener interface • ComponentAdapter class • EXAMPLE: Updating width and height in text shapes in Drawing

21. Window Events • WindowListener interface • WindowStateListener interface • WindowAdapter class • EXAMPLE: Frame window in Drawing

22. Keyboard Events • Keyboard Focus • When the user types a key, which component gets the key event? • The component with the “keyboard focus” • Only one window has the keyboard focus at a time • Within that window, only one component has the keyboard focus at a time • A component can request the keyboard focus by calling Component.requestFocus or Component.requestFocusInWindow • EXAMPLE: A text field requests the keyboard focus when the user clicks on it so it will receive key events

23. Keyboard Events • When a window receives or loses the keyboard focus, it generates “gained focus” and “lost focus” events • WindowFocusListener interface • When a component receives or loses the keyboard focus, it generates “gained focus” and “lost focus” events • FocusListener interface • EXAMPLE: In Drawing, when the frame window receives keyboard focus, DrawingFrame calls requestFocusInWindow on the DrawingComponent so it will receive keyboard events

24. Keyboard Events • KeyListener interface • KeyAdapter class • EXAMPLE: Moving shapes with arrow keys in Drawing