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What is a GUI ?• GUI – Graphical User Interface• The (visual) interface between humans and
computers• Ranging from command lines to ”Minority
Report” – style GUI• Why? Makes interfaces more intuitive – most
humans don’t like command lines…
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GUI Programming• Creating a proper GUI can be as important –
and large – a task as creating the logic• Quite a lot of topics in GUI programming
– Human perception– Task analysis– User analysis– Actual programming
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Elements in a GUI
• A GUI is usually composed by controls• A control can be a
– Text field (enabled, disabled)– Pushbutton (OK, Cancel,…)– List box (multiple items to choose from)– Check box (yes-or-no)– …
• Many types of GUI controls
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Starting simple…• For now, we will limit
ourselves to just a few GUI controls:– Text label– Text field– List– Check box– Pushbutton– Picture
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Text labels
• Probably the simplest control of all…• Usually just used for adding ”static” text – text
that does not change – to the GUI• Such texts will typically be ”helper text” for
other controls• No code needed!
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Text field
• Two common purposes:– Allow the user to enter data as text– Display text data to the user
• A text field can be ”enabled” or ”disabled”– Enabled: Data can be entered– Disabled: Data can only be displayed
• At some point we need to set or extract the text from the text field
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List box
• Essentially serves the same purpose as a text field – get text input from user
• However, in some situations we may only allow certain inputs, for instance members of a set of legal input
• When using a list control, the user can only select an item from the list
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Check box
• In some cases, the set of possible choices is limited to two options
• Often a case of either/or, or perhaps on/off• A Checkbox can only be in two states; checked
or unchecked• Nice fit for binary choices
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Pushbutton
• A pushbutton is usually used to start some kind of processing of data
• The ”input” is simply the user clicking on the pushbutton!
• Typical use: ”Now my input is ready, do something with it!”
• We all know the ”OK” button
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Picture
• Related to text labels – does not really have any functionality, but should be helpful for the user
• Increases ”recognisability” – the user can see that (s)he is at the right place
• When programming in NetBeans, a picture is just a special kind of text label…
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GUI construction
• In general, we have two options when constructing a GUI– Build it ”by hand” using Swing API– Use the NetBeans GUI Builder
• Using the GUI Builder is usually much easier than hand-coding the GUI
• Does not give you complete control, however…
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GUI construction
• Swing is a class library for creating GUIs in Java• Quite large…• API: See package javax.swing in the Java
documentation• Tutorial:
http://docs.oracle.com/javase/tutorial/uiswing/components/index.html
• Most classes begin with ”J”…
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GUI construction
• If you wish to construct a GUI manually using Swing, you usually begin by creating a JFrame
• A JFrame object is essentially an empty window, into which you can add containers for GUI controls
• Typically, you add a JPanel to the frame – the JPanel object contains the actual GUI controls
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GUI construction
public static void main(String[] args){JFrame theFrame = new JFrame();
theFrame.setBounds(200, 200, 720, 450);theFrame.setVisible(true);
JPanel thePanel = new JPanel();theFrame.add(thePanel);
}
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GUI construction
• On the JPanel object, various layout strategies can be used– Flow layout – left to right– Border layout – groups into areas– Grid layout – groups into a grid
• Border layout is default, and also most commonly used
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GUI construction
• Using border layout, the panel is divided into five areas– Center– North– South– East– West
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GUI construction
• If a control is put into an area, it will expand to fill out the area
• Good when resizing, but may look weird…• If you need a finer level of control, put a panel
inside a panel…• …or maybe consider a different layout
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GUI constructionpublic static void main(String[] args){
JFrame theFrame = new JFrame();theFrame.setBounds(200, 200, 240, 150);theFrame.setVisible(true);
JPanel thePanel = new JPanel();thePanel.setLayout(new BorderLayout());thePanel.add(new Button("Center"), BorderLayout.CENTER);theFrame.add(thePanel);
}
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Text field
• Two common purposes:– Allow the user to enter data as text– Display text data to the user
• A text field can be ”enabled” or ”disabled”– Enabled: Data can be entered– Disabled: Data can only be displayed
• At some point we need to set or extract the text from the text field
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Text fieldJFrame theFrame = new JFrame();theFrame.setBounds(200, 200, 300, 300); JPanel thePanel = new JPanel();thePanel.setLayout(new BorderLayout());
JTextField theTextField = new JTextField();thePanel.add(theTextField, BorderLayout.NORTH);
theFrame.add(thePanel);theFrame.setVisible(true);
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Text field
• Enabling a text fieldtheTextField.setEditable(true);
• Disabling a text fieldtheTextField.setEditable(false);
• Setting the text in a text fieldtheTextField.setText("Greeting
earthlings!");
• Getting the text from a text fieldString s = theTextField.getText();
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List box / Combo box
• A list (or combo) box enables the user to choose an option between many alternatives
• List box: User can only choose between specified alternatives
• Combo box: User can choose between specified alternatives, or specify choice manually (type it in)
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List box / Combo box
Object[] choices = {"One", "Two", "Three", "Four"};
JComboBox theBox = new JComboBox(choices);theBox.setEditable(true);thePanel.add(theBox, BorderLayout.NORTH);
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List box / Combo box
• Enabling a Combo boxtheBox.setEditable(true);
• Disabling a Combo boxtheBox.setEditable(false);
• Setting the selection in a Combo boxtheBox.setSelectedItem(”Three");
• Getting the selection from a Combo boxString s = (String)theBox.getSelectedItem();
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Check boxes
• In some cases, the set of possible choices is limited to two options
• Often a case of either/or, or perhaps on/off• A Check box can only be in two states;
checked or unchecked• Nice fit for binary choices
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Check boxes
JCheckBox theBBox = new JCheckBox("Bold");JCheckBox theIBox = new JCheckBox("Italic");JCheckBox theUBox = new JCheckBox("Underline");
thePanel.add(theBBox,BorderLayout.WEST);thePanel.add(theIBox,BorderLayout.NORTH);thePanel.add(theUBox,BorderLayout.EAST);
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Check boxes
• Enabling a Check boxtheCBox.setEnabled(true);
• Disabling a Check boxtheCBox.setEnabled(false);
• Setting the selection in a Check boxtheCBox.setSelected(isSelected);
• Getting the selection from a Check boxboolean isSelected = theCBox.isSelected();
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Radio buttons
• If the number of choices is few, and they are mutually exclusive, use a group of Radio buttons
• Only one button in a group of Radio buttons can be selected
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Radio buttonsJRadioButton small = new JRadioButton("Small");JRadioButton medium = new JRadioButton("Medium");JRadioButton large = new JRadioButton("Large");
ButtonGroup theGroup = new ButtonGroup();theGroup.add(small);theGroup.add(medium);theGroup.add(large);
JPanel theRadioPanel = new JPanel();theRadioPanel.setLayout(new FlowLayout());
theRadioPanel.add(small);theRadioPanel.add(medium);theRadioPanel.add(large);
thePanel.add(theRadioPanel, BorderLayout.NORTH);
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Radio buttons
• Enabling a Radio buttontheRB.setEnabled(true);
• Disabling a Radio buttontheRB.setEnabled(false);
• Setting the selection in a Radio buttontheRB.setSelected(isSelected);
• Getting the selection from a Radio buttonboolean isSelected = theRB.isSelected();
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Radio buttons
• Note that even though only one Radio button in a group can be selected, we must call isSelected() until we find it…
• Putting Radio buttons in a group does not make them appear grouped visually
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Menus
• Pull-down menu is a classic choice for choosing between options that have a hierarchical structure – menus form a hierarchy
• Usually only one main menu in an application; possible choices may vary depending on current circumstances
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Menus
• Swing menu classes: • JMenuBar – the actual menu bar, attached to
a frame window• JMenu – an element in the menu bar, with
other menus or menu items in it.• JMenuItem – a specific choice, with no sub-
choices
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Menus
• ”A menu bar contains menus”
• ”A menu contains other menus and menu items”
• ”A menu item just contains itself”
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Menus
• How to create a menu bar– Create a JMenuBar object
• JMenuBar theMenuBar = new JMenuBar();
– Add all relevant menus to the menu bar– Attach the menu bar to the main frame of the
application• frame.setJMenuBar(theMenuBar);
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Menus
• How to add menus to the menu bar– Create relevant menus, like
• JMenu borrowerMenu = new JMenu(”Borrower”);
– Add other menus or menu item to the menu– Add the menu to the menu bar
• theMenuBar.add(borrowerMenu);
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Menus
• How to add other (sub)menus to a menu– Create relevant menus, like
• JMenu borrowerManageMenu = new JMenu(”Manage Borrower”);
– Add other menus or menu item to the menu– Add the menu to the relevant menu
• borrowerMenu.add(borrowerManageMenu);
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Menus
• How to add menu items to a menu– Create relevant menu items, like
• JMenuItem borrowerDeleteMenuItem = new JMenuItem(”Delete Borrower”);
– Add the menu item to the relevant menu• borrowerManageMenu.add(borrowerDeleteMenuItem);
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Menus
• You can do some more ”fun” – and maybe even useful – things with menus:– Add images– Define accelerator keys– Use controls in menus (radio buttons, check boxes,
…)• Explore the documentation, but only use
features that are indeed useful…
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The concept of events
• On the inside (code), GUI code has a very different structure than ”usual” code
• Usual code is driven by con-ditions and various control structures (if, while,…)
• GUI code is driven by events
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The concept of events
• Execution of GUI code is much more unpredictable than for usual code
• We cannot predict – or dictate – what the user does, so we must always handle any possible action the user can do
• A user action related to the GUI is called an event
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The concept of events
• Almost all actions the user performs will ”trigger” an event for us to handle– Moving the mouse– Clicking on a button– Writing text in a text box– ….and so on
• There are hundreds of possible events!
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The concept of events
• Fortunately, is it optional to respond to an event
• We only need to do so, if we want any special action to happen
• If that is the case, we must write an event handler for that particular event
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Relevant events
• Unless we need more sophisticated behavior, we only need to handle two types of events– Choosing a menu item– Clicking on a push button
• In both cases, we must create an object which can listen for events from the control in question
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Relevant events
• An event listener class must implement a …Listener interface (there are several)
• From pushbuttons and menu items, we get ”action events”, so a listener class must implement the ActionListener interface
• This interface has a single method: actionPerformed
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Relevant eventspublic class MyListener implements ActionListener{
public void actionPerformed(ActionEvent event){
System.out.println("Button clicked");}
}
private ActionListener theListener;theListener = new MyListener();...JButton theButton = new JButton("Click Me!");theButton.addActionListener(theListener);
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Relevant events
• A very common dialog construction:– Add an ”OK” button– In the event listener for the button
• Retrieve data from the relevant controls• Process the data• Close the dialog (maybe)
• Pressing ”OK” means: ”Now my input is ready, do something with it!”
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GUI Development in NetBeans
• Manual GUI programming is somewhat difficult and tedious
• Unless you need something special, use the NetBeans GUI Builder!
• Enables you to ”drag-and-drop” controls into a pane, create event handler methods almost automatically, etc.
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GUI Development in NetBeans
• We will often start out by creating a ”main” frame for the application
• This frame could be called e.g. AppFrame• This frame will only contain a menu, to open
other – use-case specific – frames• Could e.g. also contain a logo, but should not
contain controls as such
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GUI Development in NetBeans
• Looks somewhat confusing at first…• Good news is: You can literaly drag controls
onto the frame, move them around, adjust their size, alignment, etc.
• Code that implements your ”design” is automatically generated!
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GUI Development in NetBeans
• Once we add a control, we can– Give the variable representing the control a
suitable name– Graphically move, resize, etc. the control– Set various properties for the control– Also, we can add event handlers to a control
• While all this goes on, Java code is being generated for us
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GUI Development in NetBeans
• Once we add the event handler, it cannot be removed!
• However, we can always change the code• In a sense, the event handler is always there;
we just make it visible…• In general, we are not allowed to change the
automatically generated code
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GUI Development in NetBeans• Simplistic GUIs often work as follows:
– Fill in data in the controls– Press the OK button– Data is ”dealt with” (sent to a handler, etc.)
• The only code we need to write is the event handler for pressing the OK button
• In the event handler, data is retrieved from the other controls
RHS – SOC 82
GUI Development in NetBeansprivate void jButtonDoneActionPerformed(
java.awt.event.ActionEvent evt) { String name = jTextFieldName.getText(); String job = jListJob.getSelectedValue().toString(); boolean isMale = jCheckBoxMale.isSelected();
String gender; if (isMale) gender = "Male"; else gender = "Female";
String announce = name + " , " + gender + " , " + job; JOptionPane.showMessageDialog(null, announce);}
GUI Development guide
• No two applications will need the same GUI…
• ..but a typical 1. or 2.semester application will usually follow a certain pattern
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GUI Development guide
• What should the application be able to do…?– Probably some generic tasks (Quit, Help,…)– General data management (Load, Save,…)– Implement use cases!– Uses cases often fall in groups according to their
purposes (maybe a Customer-related group, a Boat-related group, etc.)
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GUI Development guide
• The set of tasks can be used to outline a menu structure, like e.g.– File (Load, Save, Quit,…)– Customer (Register, Delete, View All, …)– Boat (Register, Delete, View All)– Rental (Create, Delete, View All,…)
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GUI Development guide
• Create a main frame for the application, and add a menu bar with proper menus
• Do this using the Net-Beans GUI builder
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GUI Development guide
• Create an event handler for each menu item, create and display the proper frame in the event handler
private void jMenuItemRegisterBoatActionPerformed(java.awt.event.ActionEvent evt) { JFrame theRegBoatFrame = new RegisterBoatFrame(); theRegBoatFrame.setVisible(true);}
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GUI Development guide
• Create frames with controls for each of the Use Cases, again using the GUI builder
• Remember to give the control variables proper names
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GUI Development guide
• In each Use Case – specific frame, retrieve data from controls, do e.g. conversions and validation if needed, and forward data to business logic
• The above is usually done when the user clicks an ”OK”/”Register”/”Done” button
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GUI Development guide
• Create an event handler for the button, and do data retrieval, conversion, validation and forwarding in the event handler
private void jButtonRegisterBoatActionPerformed(java.awt.event.ActionEvent evt) { // Retrieve data from controls, etc..}
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GUI Development guide
• Remember that even though the code for a frame is auto-generated, you can still e.g. add instance fields to the class and parameters to the constructor
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GUI Development guide
• Typical use: Give a reference to the ”System” class to the frame in its constructor, so it can be used for calling a proper method in the ”System” class with the retrieved data
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GUI Development guide// Code in red added manuallypublic class RegisterBoatFrame extends javax.swing.JFrame { private BoatRentalSystem theSystem;
public RegisterBoatFrame(BoatRentalSystem theSystem) { this.theSystem = theSystem; initComponents(); }
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