Implementing GUIs in Java

1. Implementing GUIs in Java • The Java Foundation Classes (JFC) are a set of packages encompassing the following APIs: • Abstract Window Toolkit (AWT): native GUI components • Swing: lightweight GUI components • 2D: rendering two-dimensional shapes, text, and images • Accessibility: allowing compatibility with, for example, screen readers and screen magnifiers

2. Abstract Window Toolkit (AWT) • Provides basic UI components: • Buttons, lists, menus, textfields, etc • Event handling mechanism • Clipboard and data transfer • Image manipulation • Font manipulation • Graphics • Platform independence is achieved through peers, or native GUI components

3. AWT Packages java.awt Basic component functionality java.awt.accessibility Assistive technologies java.awt.color Colors and color spaces java.awt.datatransfer Clipboard and data transfer support java.awt.dnd Drag and drop java.awt.event Event classes and listeners java.awt.font 2D API font package java.awt.geom 2D API geometry package java.awt.im Input methods java.awt.image Fundamental image manipulation classes java.awt.peer Peer interfaces for component peers java.awt.print 2D API support for printing java.awt.swing Swing components

4. Peers and Platform Independence • The first AWT (Java 1.0) was rolled out in an incredible 6 weeks using peers • Thus an AWT menu on the Solaris platform, for example, actually creates a Motif menu object as its peer • UI components that have peers are called heavyweight because • they are rendered in their own (opaque) windows and thus are expensive to use, • they must be rectangular and cannot have transparent backgrounds, and • they are not amenable to being subclassed

5. Using Peers Java Program Java AWT Native Window System Peers A Java program creates and displays an AWT component, which creates and displays a native component, or peer.

6. Lightweight Components • AWT 1.1 introduced the notion of lightweight components which: • are contained within a heavyweight component's window • do not have peers • are rendered in their container's window rather than one of their own • do not incur performance penalties and can have transparent backgrounds • Almost all Swing components are lightweight ones that extend either java.awt.Component or java.awt.Container

7. Some AWT Components Object Component Container List Button JComponent Scrollbar Label Canvas Button

8. AWT vs. Swing • Swing does not replace the AWT; it is built on top of it • All 1.0 AWT components are heavyweight; corresponding Swing components are lightweight • Swing component names begin with ``J'': • Component (AWT) vs. JComponent (Swing) • Button (AWT) vs. JButton (Swing) • Always use Swing components; however, since Swing is built on top of AWT, you will need to know some AWT methods

9. Some Swing Components JComponent AbstractButton JLabel JButton JMenuItem JList JToggleButton JScrollBar JCheckBox JFileChooser

10. JComponents • Note that JComponents are containers • JComponents do not extend their AWT counterparts: • For example, the JButton class is not a subclass (direct or indirect) of Button • However, some Swing components are not JComponents • For example, some Swing containers are direct subclasses of their AWT counterparts

11. Some AWT Containers Container JComponent Panel ScrollPane Window Applet Dialog Frame

12. Swing Components That Are Not JComponents (in red) Container JComponent Panel ScrollPane Window Applet Dialog Frame JWindow JDialog JFrame JApplet

13. Some More Swing Components That Are JComponents JComponent JLayeredPane JPanel JScrollPane JDesktopPane JInternalFrame JTable JTree

14. Some AWT Component Methods • void setBackground(Color c) • void setForeground(Color c) • void setEnabled(boolean b) • void setVisible(boolean b) • void setFont(Font f) • void setSize(Dimension d) • void setLocation(int x, int y) All but setSize and setLocation are overridden by the JComponent class.

15. Example: A Simple Framed Window import java.awt.*; import javax.swing.*; public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); frame.setVisible(true); } }

16. Notes on the Example • setSize and setLocation require java.awt.*; the rest require javax.swing.* • The JFrame constructor argument is used as a title • The Dimension constructor takes an integer width and height, respectively • The setLocation method takes a pair of integer coordinates (x,y) where (0,0) is the upper left corner of the display • The visibility of a JFrame is set to false by default

17. Example Output Display • This window was managed by the K Desktop Environment (KDE) • Clicking the Close button (X) will cause the display to be hidden, but the program will continue since no listeners are set up yet • Can use ctl-C to kill the Java Virtual Machine

18. Color.magenta Color.orange Color.pink Color.red Color.white Color.yellow Adding Color The java.awt.Color class has the following static fields (data members): • Color.black • Color.blue • Color.cyan • Color.darkGray • Color.gray • Color.green • Color.lightGray

19. Changing Background Color import java.awt.*; import javax.swing.*; public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); contentPane.setBackground(Color.red); frame.setVisible(true); } }

20. Content Panes • Q: Why not just: frame.setBackground(Color.red); ? • A: In order to be lightweight, Swing's top-level window objects must be built on top of a lightweight AWT Container object introduced in version 1.1 • This container is called a content pane • Swing top-level window classes: • JWindow • JFrame • JApplet • JDialog • JInternalFrame

21. Adding a Label and Button import java.awt.*; import javax.swing.*; public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); JLabel label = new JLabel("HERE IS A LABEL"); contentPane.add(label, BorderLayout.NORTH); JButton button = new JButton("BUTTON"); contentPane.add(button, BorderLayout.SOUTH); frame.setVisible(true); } }

22. New Display Resized

23. Notes on the Code • Since the frame is a top-level Swing window, components must be added to its content pane • When components are added to a container, how they are placed is dependent upon the container's layout manager • The default layout manager for a JFrame is a BorderLayout manager (described later) • When adding to a container whose layout manager is BorderLayout, the second parameter should be a location defined in the BorderLayout class

24. Adding a List of Options import java.awt.*; import javax.swing.*; public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); JLabel label = new JLabel("HERE IS A LABEL"); contentPane.add(label, BorderLayout.NORTH); JButton button = new JButton("BUTTON"); contentPane.add(button, BorderLayout.SOUTH); String[] options = {"Option 1", "Option 2", "Option 3"}; JList list = new JList(options); contentPane.add(list, BorderLayout.CENTER); frame.setVisible(true); } }

25. New Display Note that "Option 3" has been selected.

26. Adding a Check Box and Slider public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(400,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); JLabel label = new JLabel("HERE IS A LABEL"); contentPane.add(label, BorderLayout.NORTH); JButton button = new JButton("BUTTON"); contentPane.add(button, BorderLayout.SOUTH); String[] options = {"Option 1", "Option 2", "Option 3"}; JList list = new JList(options); contentPane.add(list, BorderLayout.CENTER); JCheckBox cbox = new JCheckBox("Check"); contentPane.add(cbox, BorderLayout.WEST); JSlider slider = new JSlider(); contentPane.add(slider, BorderLayout.EAST); frame.setVisible(true); } }

27. New Display

28. Layout Management • A layout manager determines the location and size of components placed into a container • Different layout managers use different algorithms for determining size and location: • BorderLayout: places at compass locations and center • FlowLayout: places components in rows, left to right • GridLayout: places in rectangular grid • BoxLayout: places in a single row or column

29. Changing the Layout public class SwingTest { public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); contentPane.setLayout(new FlowLayout()); JLabel label = new JLabel("HERE IS A LABEL"); JButton button = new JButton("BUTTON"); String[] options = {"Option 1", "Option 2", "Option 3"}; JList list = new JList(options); JCheckBox cbox = new JCheckBox("Check"); JSlider slider = new JSlider(); contentPane.add(label); contentPane.add(button); contentPane.add(list); contentPane.add(cbox); contentPane.add(slider); frame.setVisible(true); } }

30. New Display Resized

31. Default Layout Managers • The default layout manager for content panes is BorderLayout. Recall that the following Swing components have content panes: • JWindow • JFrame • JDialog • JApplet • JInternalFrame • The other Swing container is the JPanel, whose default layout manager is FlowLayout.

32. JPanels • A JPanel object can be used for grouping components into a container, which can then be added to another container • The JPanel constructor with no arguments creates a panel with a FlowLayout manager • Another JPanel constructor takes any layout manager as an argument • A JPanel can also be used a a blank area for drawing custom graphics

33. JPanel Example JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); JLabel label = new JLabel("HERE ARE SOME BUTTONS", SwingConstants.CENTER); JButton button1 = new JButton("BUTTON1"); JButton button2 = new JButton("BUTTON2"); JButton button3 = new JButton("BUTTON3"); JPanel panel = new JPanel(); panel.add(button1); panel.add(button2); panel.add(button3); contentPane.add(label, BorderLayout.NORTH); contentPane.add(panel, BorderLayout.CENTER); frame.setVisible(true);

34. JPanel Example Output Note use of SwingConstants.CENTER argument in JLabel constructor.

35. Changing JPanel Layout JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); JLabel label = new JLabel("HERE ARE SOME BUTTONS", SwingConstants.CENTER); JButton button1 = new JButton("BUTTON1"); JButton button2 = new JButton("BUTTON2"); JButton button3 = new JButton("BUTTON3"); JPanel panel = new JPanel(); panel.setLayout (new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(button1); panel.add(button2); panel.add(button3); contentPane.add(label, BorderLayout.NORTH); contentPane.add(panel, BorderLayout.CENTER); frame.setVisible(true);

36. New Output • The button panel is to the west because no other component was placed there • The BoxLayout constructor requires both the component being laid out and either: • BoxLayout.X_AXIS • BoxLayout.Y_AXIS

37. Tweaking Layouts • Some layout constructors allow hgap and vgap, integers specifying the number of pixels separating components horizontally and vertically • FlowLayout allows the specification of whether the line of components should be left-justified, right-justified, or centered new FlowLayout(int align) new FlowLayout(int align, int hgap, int vgap) new BorderLayout(int hgap, int vgap) new GridLayout(int rows, int cols) new GridLayout(int rows, int cols, int hgap, int vgap)

38. Tweaking Example JFrame frame = new JFrame("Test Frame"); frame.setSize(new Dimension(300,200)); frame.setLocation(100,100); Container contentPane = frame.getContentPane(); LayoutManager lm = contentPane.getLayout(); ((BorderLayout)lm).setHgap(25); JLabel label = new JLabel("HERE ARE SOME BUTTONS", SwingConstants.CENTER); JButton button1 = new JButton("BUTTON1"); JButton button2 = new JButton("BUTTON2"); JButton button3 = new JButton("BUTTON3"); JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); panel.add(button1); panel.add(button2); panel.add(button3); contentPane.add(label, BorderLayout.NORTH); contentPane.add(panel, BorderLayout.CENTER); frame.setVisible(true);

39. Tweaking Example Output • The LayoutManager returned by getLayout() is an interface type that the BorderLayout class implements • The setHgap method we want is in the BorderLayout class • So we must cast the LayoutManager to BorderLayout in order to use setHgap

40. Sizing Hints • Layout managers often need to resize their components to make things fit • For example, the widths and heights of components in a BoxLayout are adjusted according to both preferred and maximum heights and widths • If you don't like the size of the components a layout manager comes up with, you may have to give sizing hints using the following methods from the JComponent class: • void setMinimumSize(Dimension d) • void setPreferredSize(Dimension d) • void setMaximumSize(Dimension d)