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C13b, AWT cont.

This guide provides an overview of essential Java GUI components including Panels, ScrollPanes, Dialogs, and MenuBars. Panels act as containers for other components and can incorporate scroll bars when necessary. ScrollPanes automatically provide scroll functionality for larger components. Modal and non-modal Dialogs are explored for user interactions and notifications. Finally, we will delve into MenuBars, which manage application menus attached to frames, allowing for structured actions like quitting the application. Discover how to implement these components with practical examples.

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C13b, AWT cont.

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  1. C13b, AWT cont.

  2. Panel • Container that acts like a Component • Can be added into other components (like Frames, other Panels) private Panel makeScrollBars() { Panel p = new Panel(); p.setLayout(new BorderLayout()); p.add(“West”,redBar); p.add(“Center”,greenBar); p.add(“East”,blueBar); return p; }

  3. ScrollPane • Can hold exactly one other component ( no LayoutManager) • Automatic scrollbars if Component larger than ScrollPane class BigCanvas extends Frame { public static void main(String[] args) { BigCanvas w = new BigCanvas(); w.show(); } private Polygon poly = new Polygon(); private Canvas cv = new Canvas(); …

  4. public BigCanvas() { setSize(300,300); setTitle(“Scroll Pane Test”); cv.setSize(1000,1000); cv.addMouseListener(new MouseKeeper()); ScrollPane sp = new ScrollPane(); sp.add(cv); add(“Center”,sp); } public void paint(Graphics g) { Graphics gr = cv.getGraphics(); gr.drawPolygon(poly); } private class MouseKeeper extends MouseAdapter { public void mousePressed(MouseEvent e) { poly.addPoint(e.getX(),e.getY()); repaint(); }}}

  5. Case study: Color display private class BrightenButton extends Button implements ActionListener { private int index; public BrightenButton(int i) { super( i == 0 ? “brighter” : “darker”); index = i; addActionListener(this); } public void actionPerformed(ActionEvent e) { setFromColor(index == 0 ? current.brighter(): current.darker()); } }

  6. Dialogs • Special purpose window displayed shortly • To notify, or ask simple questions • Always attached to a Frame • Modal: demands user response, prevents further actions; show() won’t return until dismissed,  setVisible(false) • Nonmodal: actions often placed into separate Thread Dialog dig = new Dialog(this,false);

  7. class Dialog extends Frame { static public void main(String[] args) { DialogTest w = new DialogTest(); w.show();} private TextArea d = new TextArea(); private Checkbox cb = new Checkbox(“Modal Dialog?”); public DialogTest() { setTitle(“Dialog Test Program”); setSize(300,220); add(“West”,cb); add(“East”, new MakeButton()); add(“South”,d); } private class MakeButton extends ButtonAdapter { public MakeButton() { super(“Make Dialog”); } public void pressed() { makeDialog(cb.getState());} }

  8. private void makeDialog(boolean modalFlag) { final Dialog dlg = new Dialog(this,modalFlag); dlg.setSize(100,100); dlg.add(“North”,new CountButton(1)); dlg.add(“West”,new CountButton(2)); dlg.add(“East”,new CountButton(3)); dlg.add(“South”, new ButtonAdapter(“Hide”) { public void pressed() {dlg.setVisible(false);}}); dlg.show(); } private class CountButton extends ButtonAdapter { public CountButton(int val) {super(“” + val);} public void pressed() {d.append(“Button “ + getLabel() + “ pressed\n”); }}}

  9. MenuBar • Not subclass of component, but graphical! • Attached to Frame by setMenuBar(): MenuBar bar = new MenuBar(); setMenuBar(bar); • Add menus: Menu HelpMenu = new Menu(“Help”); bar.add(helpMenu); • Add menu items: MenuItem quitItem = new MenuItem(“Quit”); quitItem.addActionListener(new QuitListener()); helpMenu.add(quitItem);

  10. class QuitItem implements ActionListener { private void m1(MenuItem mItem) { mItem.addActionListener(this); } private void m2(Menu menu) { MenuItem mItem = new MenuItem(“Quit”); m1(mItem); menu.add(mItem); } private void m3(MenuBar mBar) { Menu menu = new Menu(“Quit”); mBar.add(menu); m2(menu); } private void m4(Frame application) { MenuBar mBar = new MenuBar(); application.setMenuBar(mBar); m3(mBar); }

  11. public QuitItem(Frame application) {m4(application);} public QuitItem(MenuBar mBar) {m3(mBar);} public QuitItem(Menu menu) {m2(menu);} public QuitItem(MenuItem mItem) {m1(mItem);} public void actionPerformed(ActionEvent e) {System.exit(0);} • Use like in: class ColorTest extends Frame { … public ColorTest() { … new QuitItem(this); … }}

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