Graphical User Interface Programming

Transcription

1 Graphical User Interface Programming Michael Brockway January 14, 2015

2 Graphical User Interfaces Users interact with modern application programs using graphical components such as windows, buttons (plain, checkbox, radio buttons), text boxes, menus, etc. Early versions of Java used the abstract windowing toolkit (AWT) for programming these. These are little used now. Instead, we mostly use the Swing classes, aka the Java Foundation Classes. These are little used now; instead we use Swing aka Java Foundation Class components. Swing ships with all recent versions of the Java standard edition toolkit, and is the recommended library of classes for programming graphical user interfaces. This lecture contains a number of Java examples: the source files a available for you to experiment with, in a companion zip archive.

3 Graphical Components A graphical interface consists of graphical components, such as: windows buttons menus text fields drop-down lists A user interacts with the application by actions such as: clicking on a button to choose a program option. making a choice from a menu. entering text in a text field. dragging a scroll bar. clicking on a window s close button

4 Event-driven Programming When you perform an action on a graphical component you generate an event. In event-driven programming the program has functions that respond to events. The program responds to events that the user generates in interacting with GUI components. The order of events is controlled by the user.

5 Java event-driven GUI Programming In Java, you can get the GUI components you want merely by asking for them. Most of the work has already been done and is contained in the Swing package. Swing contains windows, frames, buttons, menus and other components. A user interacts with a GUI application by causing events. The application must respond to events in the order they arrive. Each time the user interacts with a component, an event is sent to the application. Different events are sent to different parts of the application. The application has to work correctly no matter what the user does. Usually an application ignores events that it is not programmed to respond to.

6 Three Parts GUI Program 1. Graphical Components that make up the Graphical User Interface. Swing objects. You either use then as they are defined or extend them to your own classes. 2. Listener methods that receive the events and respond to them. You write these functions. They are called by the event-handling mechanism. Normally they in turn call application methods. 3. Application methods that do useful work Receive data from GUI components. Output data to GUI components for display. Not themselves concerned with the user interface.

7 Container Classes A GUI program consists of a collection of graphical components that are all placed inside one or more windows. You think of most components as being contained by a particular window. A container is an object that can hold other GUI components. Visually, a container is an area of the screen and the objects it contains are shown as smaller areas within it. In Java terminology, a window is a container. The buttons, sliders, icons and other GUI components are contained (by the container).

8 The AWT Hierarchy Object...(many more classes)... Component Button Canvas Container JComponent JPanel (swing)... (many swing components) Window Frame JFrame (swing) Panel Applet JApplet (swing)...(many other AWT Components)......(many classes)...

9 JFrame; JComponent and its subclasses Class JFrame, derived from java.awt.frame, is the usual main container of a GUI. The class JComponent, derived from awt.container is one of the base classes of swing. Here are some of its subclasses: JComponent AbstractButton JButton JLabel JPanel JSlider JTextComponent...(many more classes)...

10 Frames In Java, a frame is an outside window... that has nice borders, various buttons along the top border, and other built-in things. What you usually call a window Java calls a frame. A frame is a container object: GUI components can be placed in it. GUI-based application programs are usually organized around one or more frames.

11 Elements of a Frame

12 Small GUI Example - TestFrame1.java import java.awt.*; import javax.swing.*; public class TestFrame1 { private JFrame frame; public TestFrame1() { makeframe(); private void makeframe() { frame = new JFrame("Test Frame 1"); frame.setsize(200,100); frame.setvisible( true );

13 Small GUI Example: Comments The AWT is imported since it defines many classes that GUIs use. Not strictly mecessary here but most GUI programs must do this. Events are encapsulated by classes in the AWT package java.awt.* The Swing package is imported since that is where JFrame is defined. Notice the x in javax.swing.*. A JFrame object is constructed. The reference variable frame refers to the JFrame object. The object s setsize() method sets its width and height in pixels. The object s setvisible() method makes it visible on the screen. A call to setvisible(false) makes the frame invisible, but does not destroy the software object

14 Another Example: Extending the Frame Class A common way of writing a GUI is to define your own class by extending the JFrame class In the following example The class MyFrame extends the class JFrame MyFrame objects will be automatically re-painted when needed. The standard parts of the frame the background, the borders, the controls are drawn automatically by the Java system.

15 TestFrame2.java public class TestFrame2 extends JFrame { public TestFrame2() { super("test Frame 2"); makeframe(); private void makeframe() { setsize(200,100); setvisible( true );

16 Closing a Frame (Main Window) By default, when the user closes a frame with the close button, the frame is hidden. The frame is then invisible, the frame still exists and the program can make it visible again. If you want different behaviour, then you need to either register a window listener that handles window-closing events, or you need to specify default close behaviour using the setdefaultcloseoperation method:... public class TestFrame2 extends JFrame { //... (constructor as before) private void makeframe() { setsize(200,100); setvisible( true ); setdefaultcloseoperation(jframe.exit_on_close);

17 setdefaultcloseoperation(...); DO NOTHING ON CLOSE Don t do anything when the user requests that the window close. Instead, the program should probably use a window listener that performs some other action in its windowclosing method. HIDE ON CLOSE (the default for JDialog and JFrame) Hide the window when the user closes it. This removes the window from the screen but leaves it displayable. DISPOSE ON CLOSE (the default for JInternalFrame) Hide and dispose of the window when the user closes it. This removes the window from the screen and frees up any resources used by it. EXIT ON CLOSE (defined in the JFrame class) Exit the application, using System.exit(0).

18 Two special Java methods System.exit(int) causes program to finish a value 0 says no error mywindow.dispose() removes the window from the screen

19 Events and Event Handling When a GUI program is running, the user generates an event by interacting with a GUI component For a program to respond to an event there must be an event listener for it. The event listener object contains listener methods for various types of events If there is no listener for an event, the event is ignored.

20 Event Objects Events in Java are encapsulated in objects A WindowEvent object represents an event sent by a window (resize, close,...); An ActionEvent object represents an event sent by a button, text field, or menu; An ItemEvent object represents an event from a checkbox, choicebox, or list (choice of an item); A TextEvent represents an event from a text component An AdjustmentEvent represents an event from a scrollbar A KeyEvent represents an event from a key (press, release) A MouseEvent or MouseMotionEvent represents events a mouse (click, press, release, drag,...).

21 Event Listener Objects When an event is sent by the GUI component, a method in the listener is to be invoked. An event listener is an object in the program. In particular, for each event the program must respond to, the program must create an event listener object for the type of event. register the listener object with the GUI component that generates the event (or with a component that contains it.)

22 ButtonDemo1.java: A program with a button import java.awt.*; import java.awt.event.*; import javax.swing.*; public class ButtonDemo1 extends JFrame { private JButton bchange; public ButtonDemo1() { // constructor super("button Demo"); makeframe(); private void makeframe() { bchange = new JButton("Click Me!"); // construct a Button add( bchange ); // add it to frame setdefaultcloseoperation(jframe.exit_on_close); setsize(200, 150); setvisible(true);

23 Comments To construct a JButton object, use new. Then add the button to the frame s content pane. The JButton now will be displayed when the frame is displayed, and respond visually when the user clicks on it. Clicking on the button generates events, but so far, there is no event handling. Also the button fills the whole content pane. We shall deal with this first, then return to the event handling.

24 Layout Managers When you add() buttons (and other components) to a content pane, a layout manager automatically decides what size they will be and where they will go. convenient, because you can add components without worrying about the details. You say what components you want and the layout manager lays them out in the picture. The layout manager sometimes makes odd choices. There are several kinds of layout managers; each one has a different style of positioning components. They are all classes in java.awt.

25 Layout Managers FlowLayout Components are set to a reasonable preferred size then positioned within container in the order they are added starting from top left, working from left to right; When available width is used, next row is started. GridLayout Number of rows and number of columns is specified; Components are set to a reasonable preferred size then positioned down the first column, then down the second column, etc. BorderLayout Components are assigned to North, South, East, West and Center regions of the container; they are sized to fill the whole of their region.

26 Setting the Layout Manager The problem with the example is that the content pane of a JFrame has a BorderLayout by default The button expands to fill the whole content pane due to BorderLayout policy. We fix this by using setlayout(new FlowLayout()) to override the default. (See also ButtonDemo2.java in the example sources archive.)... private void makeframe() { setlayout(new FlowLayout()); //set the layout bchange = new JButton("Click Me!"); // construct a Button add( bchange ); // add it to frame setdefaultcloseoperation(jframe.exit_on_close); setsize(200, 150); setvisible(true);

27 Result with Flow Layout Manager Only one item has been added to the flow layout: it is centred in the first (top) row of the flow layout.

28 Action Listener Back to the job of handling the event of a click on the button. We need an ActionListener object. This is a class which implements the java.awt.event.actionlistener interface. Interface ActionListener declares the single method: public void actionperformed( ActionEvent evt) ; The ActionEvent parameter it expects is a java.awt.event.actionevent object that represents an event (a button click). It contains information that can be used in responding to the event. Since ActionListener is an interface, you use it with a class that will implement the actionperformed() method. It is common to implement the interface in the same class that contains the button(s):

29 Button Example with Action Listener (1 of 2) ButtonDemo2.java import java.awt.*; import java.awt.event.*; //need this for ActionListener import javax.swing.*; public class ButtonDemo2 extends JFrame implements ActionListener { private JButton bchange; public ButtonDemo2() { super("button Demo"); makeframe(); // constructor

30 Button Example with Action Listener (2 of 2) private void makeframe() { setlayout(new FlowLayout()); // set the flow layout bchange = new JButton("Click Me!"); // construct a Button add( bchange ); // add it to frame bchange.addactionlistener(this); // Register listener setdefaultcloseoperation(jframe.exit_on_close); setsize(200, 150); setvisible(true); // Method to handle the button click // (required by implments contract) public void actionperformed(actionevent evt) { getcontentpane().setbackground(color.blue);

31 Result with ActionEvent Handling Before: After:

32 Summary so far General form of actionperformed: public void actionperformed(actionevent evt) { //look at data in ActionEvent: this may be useful //send reults to GUI components (invoke methods on them) General structure for GUI code: Declare widget Define attributes of widget Text, Colour, Editable?, Size,... Add to container Register an action listener Click on an ActionEvent source (eg button) creates an ActionEvent object which is sent to the actionperformed() methods of all ActionListeners registered with it.

33 A Further Example Develop a new program: A frame will hold two buttons, one labelled Red, the other Green. Use a FlowLayout layout manager so the buttons will be nicely positioned in the frame. When the button marked Red is clicked, the background will turn red. When the button marked Green is clicked, the background will turn green. There will be an event listener that listens to the clicks from both buttons. When the close button of the frame is clicked, the application will quit.

34 Questions to consider How many frames are there? What GUI components will it/they contain? What objects generate events? What objects receive events?

35 Questions to consider Just one frame, contining the Red button and the Green button. Both buttons send ActionEvents. The frame sends a WindowEvent (handled by default close operation).

36 TwoButtons.java (1 of 3) import java.awt.*; import java.awt.event.*; import javax.swing.*; public class TwoButtons extends JFrame implements ActionListener { private JButton redbutton, grnbutton; public TwoButtons() { super ("Two Buttons"); makeframe();

37 Two Buttons: (2 of 3) private void makeframe() { redbutton = new JButton("Red"); grnbutton = new JButton("Green"); setlayout(new FlowLayout()); add(redbutton); add(grnbutton); redbutton.addactionlistener(this); grnbutton.addactionlistener(this); setdefaultcloseoperation( JFrame.EXIT_ON_CLOSE); setsize( 200, 150 ); setvisible(true);

38 Two Buttons: (3 of 3) public void actionperformed( ActionEvent evt) { // check which command has been sent if (evt.getactioncommand().equals("red")) getcontentpane().setbackground(color.red); else if (evt.getactioncommand().equals("green" )) getcontentpane().setbackground(color.green); Method getactioncommand() returns a string. In case of a button this is by default the label on the button.

39 An Alternative actionperformed Method ActionEvents have a method getsource() which returns an Object: the GUI component which sent the event. The actionperformed method can use getsource() to decide which button was clicked. public void actionperformed( ActionEvent evt) { // check which button sent the event if (evt.getsource() == redbutton) getcontentpane().setbackground(color.red); else if (evt.getsource() == grnbutton) getcontentpane().setbackground(color.green);

40 Output

41 Swing components JTextField and JLabel A JTextField is a box that contains text. The user can type text into the box and the program can get it and then use it as data. The program can write the results of a calculation to a JTextField Constructors JTextField() JTextField(String text) JTextField(int columns) JTextField(String text, int columns) A JTextField is used for input: when ENTER is typed, it issues an ActionEvent. A JLabel object simply displays text Constructor JLabel(String text) Useful for labelling other components: sych as JTextFields!

42 JTextField and JLabel Example (1 of 3) CharCounter.java User types text into upper text field and types ENTER Character count is then calculated and displayed in lower text field.

43 JTextField and JLabel Example (2 of 3) import java.awt.*; import java.awt.event.*; import javax.swing.*; public class CharCounter extends JFrame implements ActionListener { private JLabel inlabel = new JLabel("Enter text:"); private TextField intext = new TextField(15); private JLabel outlabel = new JLabel("Character count:"); private TextField outtext = new TextField(8);

44 JTextField and JLabel Example (3 of 3) public CharCounter() { //constructor super("character Counter"); setlayout(new FlowLayout()); add(inlabel); add(intext); add(outlabel); add(outtext) ; intext.addactionlistener(this); outtext.seteditable(false); setdefaultcloseoperation( JFrame.EXIT_ON_CLOSE); setsize(300, 120); setvisible(true); public void actionperformed(actionevent evt) { String stg = intext.gettext(); outtext.settext(""+stg.length());

45 seteditable() Notice outtext.seteditable(false); above. Use this JTextField method to prevent the user from entering text into the text field: The seteditable() method has one boolean parameter: true field can be edited by user false field cannot be edited by user In summary, common JTextField methods are String gettext() void settext(string s) seteditable(boolean b) boolean iseditable() void setbackground(color c) void addactionlister(actionlistener l)

46 JTextArea Similar to text field, but allows multiple lines Does not generate ActionEvent on ENTER, so not suitable for input Constructors JTextArea() JTextArea(String text) JTextArea(int rows, int columns) JTextArea(String text, int rows, int columns) Common methods String gettext() void settext(string s) append(string s) seteditable(boolean b) boolean iseditable() void setbackground(color c) void setlinewrap(boolean b) - enable/disable wrapping void setwrapstyleword(boolean b) - wrapping on complete words only

47 JTextArea Default behavior is to expand width-wise as text fills the area. setlinewrap(true) to make it wrap text to the following line. setwrapstyleword(true) to make it wrapping on whole words. With these settings the text area does not expand with-wise but does expand length-wise when it fills. You can also give the text area scroll-bars by adding it to the container inside a JScrollPane a research exercise for you!

48 JTextArea Example (1 of 3): TextAppender.java User types text into upper text field and types ENTER The text is appended to the text in the lower text area. The text in the text area wraps on whole words.

49 JTextArea Example (2 of 3) import java.awt.*; import java.awt.event.*; import javax.swing.*; public class TextAppender extends JFrame implements ActionListener { private JLabel inlabel = new JLabel("Enter text:"); private TextField intext = new TextField(15); private JLabel outlabel = new JLabel("Accumulated text:"); private JTextArea outtext = new JTextArea(10, 15); public TextAppender() { //constructor super("text Appender"); setlayout(new FlowLayout()); add(inlabel); add(intext); add(outlabel); add(outtext) ; intext.addactionlistener(this);...

50 JTextArea Example (3 of 3) outtext.seteditable(false); outtext.setlinewrap(true); outtext.setwrapstyleword(true); setdefaultcloseoperation( JFrame.EXIT_ON_CLOSE); setsize(300, 300); setvisible(true); public void actionperformed(actionevent evt) { String stg = intext.gettext(); intext.settext(""); if (outtext.gettext().length() == 0) outtext.settext(stg); else outtext.append("; "+stg);

51 Design of an Application Design and implement a GUI application that converts a temperature expressed in Fahrenheit into Celsius. There are three parts to the design: 1. The Graphical User Interface. 2. Listener methods. 3. Application methods. First look at the application methods. The formula for converting Fahrenheit into Celsius is this: C = (F 32) 5/9

52 Program Architecture We shall have two classes: 1. a temperature class 2. a GUI class The temperature class FTemperature.java models the data: public class FTemperature { private double ftemp; public FTemperature() { //constructors public FTemperature(double ft) { ftemp = ft; public void setftemp(double ft) { ftemp = ft; public double getftemp() { return ftemp; public double convftoc() { return ((ftemp-32.0) * 5.0) / 9.0;

53 The GUI: 1 of 3 FToCGUI.java: preliminary version The user enters text (a String) into the Fahrenheit text field. The string will be converted into double format. The GUI consists of JLabels and JTextFields placed into a JFrame

54 The GUI: 2 of 3 import java.awt.*; import java.awt.event.*; import javax.swing.* ; import java.text.*; public class FToCGUI extends JFrame implements ActionListener { private JLabel title = new JLabel("Convert temp F to C"); private JLabel inlabel = new JLabel("Fahrenheit"); private JLabel outlabel = new JLabel("Celsius"); private JTextField infahr = new JTextField(7); private JTextField outcel = new JTextField(7);...

55 The GUI: 3 of 3 public FToCGUI() { //constructor super("f To C"); setlayout( new FlowLayout() ); add(title); add(inlabel); add(outlabel); add(infahr); add(outcel); infahr.addactionlistener(this); outcel.seteditable(false); setdefaultcloseoperation(jframe.exit_on_close); setsize(180, 150); setvisible(true); public void actionperformed( ActionEvent evt) { String userinput = infahr.gettext() ; double ft = Double.parseDouble(userInput); FTemperature temp = new FTemperature(ft); outcel.settext(string.format("%5.2f", temp.convftoc()));

56 Notes The FTemperature class knows nothing about the programs input, output. The FToCGUI needs to know about the FTemperature class: its actionperformed method constructs an instance and sends messages to it. NB the String.format() function: uses C-style formatting to make a display string with 5 digits and 2-place rounding. There is a problem with the prelminary version of FToCGUI: when the user resizes the window, the layout goes awry, the labels becoming separated from their text boxes. We need panels to fix this.

57 Panels, JPanel and Layout A panel is a container for components that does not create a window of its own. A logical rectangle on the screen. to help organise layout add components to a panel nested them: add components, panels to bigger panels or frame a panel is both a component and a container. JPanel is the swing version of a panel. Components added to a panel become inseparable. A panel corresponds to a rectangular section of the screen. Each panel has its own layout manager that lays out the components inside the panel. The default layout manager of JPanel is flow The content pane s layout manager arranges the panels as if each one were a single component. Panels do not have visible edges.

58 JPanel Example: FToCGUI.java Here is another version of the FToCGUI constructor: public FToCGUI() { //constructor super("f To C"); JPanel p1 = new JPanel(); p1.setlayout(new GridLayout(2,1)); JPanel p2 = new JPanel(); p2.setlayout(new GridLayout(2,1)); p1.add(inlabel); p2.add(outlabel); p1.add(infahr); p2.add(outcel); JPanel p3 = new JPanel(); //default layout = flow p3.add(p1); p3.add(p2); setlayout(new GridLayout(2,1)); add(title); add(p3); infahr.addactionlistener(this); outcel.seteditable(false); setdefaultcloseoperation(jframe.exit_on_close); setsize(180, 150); setvisible(true);

59 JPanel Comments The panel p1 uses a grid layout to hold the input box underneath its label; The panel p2 uses a grid layout to hold the output box underneath its label; These two compound components are added to panel p3 side by side, since default layout is flow; The title and p3 are added to the frame using grid layout. The point of all this is that the layout is more robust against resizing by the user. Compare the resizing behaviour of this with the earlier version.

60 Radio Buttons - JRadioButton Radio buttons generate action events just as do push buttons. Use addactionlistener(actionevent). Use setactioncommand(string) if you want your code to use getactioncommand() to recognise a paticular JRadioButton. Normally radio buttons are placed in groups in two ways: in a JPanel, to control how they are displayed, and also in a javax.swing.buttongroup, to control which buttons may be active simultaneously. Clicking a radio button deselects all other buttons in the group A button group is an object which must be constructed. Radio buttons are then added to it. Use boolean rbtn.isselected() to tell whether JRadioButton rbtn is selected.

61 JRadioButton Example: RadioButtons.java A simple calculator adds, substract, multiplies integers; Input is via two JTextFields; output is to a non-editable JTextField. You choose operation using three JRadioButtons in a ButtonGroup. Displays answer in decimal or hex: choose using two JRadioButtons in a ButtonGroup. See RadioButtons.java in example sources bundle.

62 JRadioButton Example ctd Look at constructor: Operation choice radio buttons are added to a JPanel for display at top; Display format choice radio buttons are added to a JPanel for display at bottom; The text boxes are each put in a JPanel with their label; The five JPanels are put in the frame (using another JPanel!) All JTextFields and JRadioButtons assigned an ActionListener. Look at the actionperformed method: ENTER in a text box, click on a radio button all trigger the same action (otherwise we could use getactioncommand() or getsource() to decide what to do); isselected() is used to see which operation is chosen; isselected() is used to see which output format is active;

63 Border Layout: BorderLayoutEx.java Default for JFrame s ContentPane; Organises window into 5 regions: BorderLayout.NORTH, BorderLayout.SOUTH, BorderLayout.EAST, BorderLayout.WEST, BorderLayout.CENTER Each region holds only one item, but it can be a JPanel or other container holding several components.

64 Border Layout in RadioButtons.java The simple calculator example uses BorderLayout: look again at its constructor. EAST, WEST not used; they shrink to a small (zero!) size. The operation choice radio button panel is NORTH. The output format choice radio button panel is SOUTH. The three text boxe panels are in an outer JPanel in the CENTER.

65 Mouse Event Handling Java provides two event listener interfaces for dealing with mouse events java.awt.event.mouselistener listens for MouseEvents generated when the mouse has a button pressed, released, or clicked, or when it enters or exits the bounds of the component. java.awt.event.mousemotionlistener listens for MouseEvents generated when the mouse is dragged or moved across the component. (Dragged = moved with a button down) MouseListener methods mouseentered(mouseevent evt); mouseexited(mouseevent evt) mousepressed(mouseevent evt) mousereleased(mouseevent evt) mouseclicked(mouseevent evt) MouseMotionListener methods mousemoved(mouseevent evt); mousedragged(mouseevent evt) java.awt.event.mouseevent has methods to report mouse coordinates and button state: refer to API documentation.

66 Example - MouseTracker.java A simple example: implements all mouse methods and report mouse position and button status on console: import java.awt.*; import java.awt.event.*; import javax.swing.*; public class MouseTracker extends JFrame implements MouseListener, MouseMotionListener { public MouseTracker () { super("demonstration of Mouse Events"); addmouselistener (this); addmousemotionlistener(this); setdefaultcloseoperation(exit_on_close); setsize(400, 300); setvisible(true);...

67 Example - continued //helper public void smsg(string legend, MouseEvent evt) { System.out.printf("%s at [%d, %d]; button state = %d\n", legend, evt.getx(), evt.gety(), evt.getbutton()); //MouseListener methods... public void mouseclicked(mouseevent e) {smsg("clicked", e); public void mousepressed(mouseevent e) {smsg("pressed", e); public void mousereleased(mouseevent e) {smsg("released",e); public void mouseentered(mouseevent e) {smsg("entered", e); public void mouseexited (MouseEvent e) {smsg("exited", e); //MouseMotionListener methods public void mousedragged (MouseEvent e) {smsg("dragged", e); public void mousemoved (MouseEvent e) {smsg("moved", e);

68 Another Example; with low-level Graphics A slightly more amusing example is ClickMe.java

69 ClickMe Example ctd A simple reaction-timing game The game window is a single JPanel, in CENTER, plus a status display, SOUTH A string Click me is displayed in a random position on the game window and the time elapsed until a mouse click lands near it is displayed in the status display. A JPanel can be painted on using the low-level graphics methods of the java.awt.graphics object associated with the JPanel. Provide a method PaintComponent(Graphics g) in the game class, which extends the JPanel. It starts with super.paintcomponent(g) to paint the underlying JPanel, then does game-specific painting. Do not usually call super.paintcomponent() directly; rather, call JPanel s repaint() method to queue a repaint of the window.

70 PaintComponent(Graphics) In ClickMe.java... public void paintcomponent(graphics g) { super.paintcomponent(g); if (newpos) { //If target moved, g.setcolor(getbackground()); // erase it g.drawstring("click me!", x, y); x = rng.nextint(getwidth()-60); // new random y = 20+rng.nextInt(getHeight()-25); // coordinates reftime = System.currentTimeMillis(); newpos = false; if (x >=0 && y >=0) { //except for initial paint, g.setcolor(color.red); // show tgt at current g.drawstring("click me!", x, y); // position

71 Dialogues Displayed to give information or solicit input Modal dialogues block all other interaction until dismissed Non-modal dialogues allow other interaction; may be undesirable javax.swing.joptionpane provides some standard dialogues Message dialogue: message text plus an OK button. Confirm dialogue has yes/no/cancel options Input dialogue has a prompt and an input field; OK/cancel buttons

72 Message Dialogue: Dialogues.java... JOptionPane.showMessageDialog(frame, "The message", "Title", JOptionPane.INFORMATION_MESSAGE);... The last parameter chooses the information icon.

73 Confirm Dialogue: Dialogues.java... int cnf = JOptionPane.showConfirmDialog(frame, "Question?"); System.out.printf("The result was %d\n", cnf);... YES 0, NO 1, CANCEL 2

74 Input Dialogue: Dialogues.java... String inp = JOptionPane.showInputDialog(frame, "Input your data", "Input Dialogue", JOptionPane.QUESTION_MESSAGE); System.out.printf("The input was %s \n", inp);... The last parameter chooses the question icon. The return value on OK is the input string; CANCEL null