Java swing

Editor's Notes

• #4: JFC is Swing, AWT, Accessibility, 2D graphics and Drag and Drop The Swing pacakges are accessibility, swing, swing.border, swing.colorchooser, swing.event, swing.filechooser, swing.plaf, swing.table, swing.text, swing.text.html. swing.text.html.parser, swing.text.rtf, swing.tree and swing.undo MFC was Microsoft Foundation Classes, the set of C++ classes representing GUI components.
• #5: The AWT components are 'heavyweight', in the sense that the correspond to an underlying OS element. For example a Frame in MS Windows is a Window as far as the OS is concerned. Most Swing components are 'lightweight', in the sense that they are coded in Java and do not correspond to OS things. They therefore do not have all the data linked to an OS GUI object (much of which is not needed) so is faster with less memory.
• #6: Threads run at the same time. Problems arise if one thread alters things in another thread, without them being synchronised. In this situation a typical issue is when code in one thread alters a component attribute (say the colour of a button) while another thread is drawing the component - the result is unpredictable, depending on the exact timing (called a race condition). The (pretty obscure) solution used in these examples follows what is suggested by Sun in their Swing tutorial.
• #7: All teh code to set up and start the GUI is placed in the static method createAndShowGUI
• #8: First we construct a JFrame (a GUI window) with a title. The .setDefaultCloseOperation sets what will happen when the frame is closed - the application exits. Then we construct a label. .getContentpane() gets hold of the 'front drawing part' of the frame. The label is added to this. frame.pack() adjusts the size of the frame to fit what is inside it. A frame is by default not visible, and setVisible(true) makes it visible.
• #10: frame.setLayout(null); means that we will detrmine the size and position of components. frame.setBounds gives the screen co-ordinates of the top left corner (20,30) and the width (300) and height(100) of the frame. Then we make a button, add it, then setBounds fixes its position and size.
• #11: When a button is clicked, an Event object is constructed (actually a subclass of Event). The Event is passed to an object which has been designated as the Listener of the button. The Event is received as a parameter by a method of the listener. In the case of a button, the method is called actionPerformed Different components produce different events, which must be handled by different methds. The set of methods is the appropriate interface. A JButton, for example, produces ActionEvents, which are handled by teh method in the ActionListener interface.
• #14: We need an object to listen to the button. We also need to remember the number of clicks. We do this by instantiating an application object ( Main app = new Main(); ). We set this as the object which listens to the button is butt.addActionListener(app); This means that Main must implement the ActionListener interface. The label is an application object field - that way the actionPerformed method can refer to it. In a static context (in createAndShowGUI) qwe must refer to it as app.label Source code is: import javax.swing.*; import java.awt.event.*; public class Main implements ActionListener { private static void createAndShowGUI() { // make frame.. JFrame frame = new JFrame("I am a JFrame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,300,100); frame.getContentPane().setLayout(null); // make a button JButton butt=new JButton("Click me"); frame.getContentPane().add(butt); butt.setBounds(20, 20, 200,20); // instantiate an application object Main app = new Main(); // make the label app.label = new JLabel("0 clicks"); app.label.setBounds(20,40, 200,20); frame.getContentPane().add(app.label); // set the application object to be the thing which // listens to the button butt.addActionListener(app); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { // this executes when button is clicked clickCount++; label.setText("Clicks = "+clickCount); } public static void main(String[] args) { // start off.. SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields int clickCount=0; JLabel label; }
• #16: Change the last example to hav e2 buttons. The 2 buttons must be application object fields, not local to the static method createAndShowGUI
• #17: plaf = pluggable look and feels display windows and components with differing appearance.
• #18: See next slide for how to determine choices of a laf
• #20: Results in the fancy border and title area as shown. Call this before the JFrame is constructed.
• #21: Well I think 451 is a lot.
• #22: The top level containers are not contained in anything else (although normally an applet is inside a browser window). The others can be nested. So you can have a panel in a frame, and in turn a panel in a panel.
• #23: A frame has a default rootpane o which you can display things - get this by making the thing, then saying frame.getContentPane.add(thing); In this example we are making our red panel to be the 'front' of the window by using setContentPane
• #24: In other words all the JComponents can have a border and a tooltip - and lots other things. See the API spec of JComponent
• #25: The tooltip appears on the mouse cursor when held over it for a second or 2. Useful to tell users what a button will do before they click it.
• #27: Putting panels in teh left and right part of a splitpane
• #28: Start with last example. The right panel must be an application object field, so you can refer to them in actionPerformed Add 3 buttons to the left panel (they also must be application object fields) In actionPerformed you must find out which button was pressed, and change the panel colour accordingly.
• #30: An ActionPerformed event is produced when the user hits Enter on the text field. Source code: import javax.swing.*; import java.awt.event.*; import java.awt.*; public class Main implements ActionListener { private static void createAndShowGUI() { Main app=new Main(); // make frame.. JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("I am a JFrame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,300,120); frame.setLayout(null); // make a panel JPanel myPanel = new JPanel(); // make a text field app.textField = new JTextField("Type here",20); myPanel.add(app.textField); // set up action listener app.textField.addActionListener(app); // make and add label app.label = new JLabel("Result"); myPanel.add(app.label); frame.setContentPane(myPanel); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { // this happens when Enter hit on the text field label.setText(textField.getText()); } public static void main(String[] args) { // start off.. try { UIManager.setLookAndFeel( "javax.swing.plaf.metal.MetalLookAndFeel" ); } catch (Exception e) { System.out.println("Cant get laf"); } SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JLabel label; JTextField textField; }
• #32: In the AWT some components could have scroll bars. In Swing a ScrollPane can be created as a 'viewport' onto any component, so in effect anything can have scrollbars. You tell the scroll pane what to 'look at' by supplying it as an argument to the constructor. By default, scroll bars appear when they are needed.
• #33: The textarea will need to be an application oject field
• #34: There are 3 Timer classes in J2SE - this is javax.swing.Timer A timer object fires an ActionPerformed event at regular intervals once started. The constructor is given the object to listen to these events, together with the delay in milliseconds.
• #35: The second argument to the constructor is an 'alt text' for accessibility software.
• #36: A scrollbar has a 'value' which is the setting of teh slider. The arguments to the JScrollBar constructor are: whether it is horizontal or vertical the initial value the step change minimum value maximum value When the user moves a scrollbar, an AdjustmentEvent is contructed, which goes through the AdjustmentListener interface, with just one method as show. import javax.swing.*; import java.awt.event.*; public class Main implements AdjustmentListener { private static void createAndShowGUI() { // make frame.. JFrame frame = new JFrame("JScrollBar"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,200,200); frame.getContentPane().setLayout(null); Main app = new Main(); app.sbar = new JScrollBar(java.awt.Adjustable.VERTICAL, 127, 1,0,255); app.sbar.setBounds(20,20, 20, 200); app.sbar.addAdjustmentListener(app); frame.getContentPane().add(app.sbar); app.label = new JLabel(); app.label.setBounds(50,20,100,20); frame.getContentPane().add(app.label); frame.setVisible(true); } public void adjustmentValueChanged(AdjustmentEvent e) { label.setText("Value = "+e.getValue()); } public static void main(String[] args) { // start off.. SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JScrollBar sbar; JLabel label; }
• #37: Start with the last example. Just do the red slider first, then add the other two. Use the setBackground() methdo to change the colour of the scrollbar.
• #38: The isSelected method tells you whether it is checked or not. Source code: import javax.swing.*; import java.awt.event.*; import java.awt.*; public class Main implements ActionListener { private static void createAndShowGUI() { // make frame.. JFrame frame = new JFrame(".."); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,70,150); frame.getContentPane().setLayout(null); Main app = new Main(); app.checkBox = new JCheckBox("Black?"); app.checkBox.setBounds(10,20,100,20); frame.getContentPane().add(app.checkBox); app.checkBox.addActionListener(app); app.panel = new JPanel(); app.panel.setBounds(10,50,50,50); app.panel.setBackground(new Color(255,255,255)); frame.getContentPane().add(app.panel); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { if (checkBox.isSelected()) panel.setBackground(new Color(0,0,0)); else panel.setBackground(new Color(255,255,255)); } public static void main(String[] args) { // start off.. SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JCheckBox checkBox; JPanel panel; }
• #40: A ButtonGroup object is not visible. Instead it controls the behaviour of teh radio buttons which have been added to it - so that only one out of that group can be 'on'. Source code: import javax.swing.*; import java.awt.event.*; import java.awt.*; public class Main implements ActionListener { private static void createAndShowGUI() { // make frame.. JFrame frame = new JFrame(".."); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,70,150); frame.getContentPane().setLayout(null); Main app = new Main(); app.panel = new JPanel(); app.panel.setBounds(10, 60, 100,100); app.panel.setBackground(Color.red); frame.getContentPane().add(app.panel); app.choice1 = new JRadioButton("Black"); app.choice2 = new JRadioButton("White"); app.choice1.addActionListener(app); app.choice2.addActionListener(app); ButtonGroup group = new ButtonGroup(); group.add(app.choice1); group.add(app.choice2); frame.getContentPane().add(app.choice1); frame.getContentPane().add(app.choice2); app.choice1.setBounds(10,10,100,20); app.choice2.setBounds(10,40, 100,20); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { if (choice1.isSelected()) panel.setBackground(new Color(0,0,0)); if (choice2.isSelected()) panel.setBackground(new Color(255,255,255)); } public static void main(String[] args) { // start off.. SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JRadioButton choice1, choice2; JPanel panel; }
• #42: A ButtonGroup is not visible, so usually a visual clue is needed to show the user which are the alternative choices. The solution shown here is to have a panel with a border, and add the radio buttons to the panel.
• #43: Swing components have a 'model-view-controller' architecture. Usuallu you can ignore this, but for a list box it helps. The model holds the data in the component - eg the text in a text field The view controls what it looks like on screen. The controller controls the behaviour of the compenent eg what happens when you click a radio button. For a listbox, the model involves storing the listbox data in an array (or a Vector - see next example) The listbox needs to be put into a scrollpane if you want scroll bars. .getSelectedIndices returns an array of which items are selected. In the state shown on teh slide, this array would have elements 1,3 since these are the ones selected (starts at 0). .getModel() gets the array which holds the data, and getElementAt gets an element from that. Source code import javax.swing.*; import java.awt.event.*; import java.awt.*; public class Main implements ActionListener { private static void createAndShowGUI() { Main app=new Main(); // make frame.. JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("Demo JList"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,300,200); frame.getContentPane().setLayout(null); // make array to hold values.. String listContents[] = {"One", "Two", "Three","Four","Five","Six"}; // make a ListBox using this data app.myList = new JList(listContents); app.myList.setBounds(0,0,100,100); // make a scrollpane using this listbow JScrollPane myScrollPane = new JScrollPane(app.myList); myScrollPane.setBounds(10,10, 140, 80); frame.getContentPane().add(myScrollPane); //add button JButton myButton= new JButton("Show first"); myButton.setBounds(10, 100, 100,20); frame.getContentPane().add(myButton); myButton.addActionListener(app); // add label app.myLabel = new JLabel("First shown here"); app.myLabel.setBounds(130,100,100, 20); frame.getContentPane().add(app.myLabel); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { // get array of which items are selected // get indices, not the actual items int select[] = myList.getSelectedIndices(); if (select.length>0) // if anything selected myLabel.setText((String)myList.getModel().getElementAt(select[0])); else myLabel.setText("No selection"); } public static void main(String[] args) { // start off.. try { UIManager.setLookAndFeel( "javax.swing.plaf.metal.MetalLookAndFeel" ); } catch (Exception e) { System.out.println("Cant get laf"); } SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JLabel myLabel; JList myList; }
• #44: A Vector ( in java.util ) is like an array, except that its size can be altered at run-time. This is convenient here when we want to insert new things into a listbox. A Vector is declared to hold Object type. So when you get something out of a Vector, you have to typecast it to the actual type (which here is String). Source code: import javax.swing.*; import java.awt.event.*; import java.awt.*; import java.util.*; public class Main implements ActionListener { private static void createAndShowGUI() { Main app=new Main(); // make frame.. JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("Demo JList"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,400,200); frame.getContentPane().setLayout(null); // make vactors.. app.listContents= new Vector(); app.vector2 = new Vector(); // make a ListBox app.myList1 = new JList(app.listContents); app.myList1.setBounds(0,0,100,100); app.myList1.setBackground(Color.yellow); app.myList1.setSelectionBackground(Color.blue); app.myList1.setSelectionForeground(Color.white); // make a scrollpane using this listbox JScrollPane myScrollPane = new JScrollPane(app.myList1); myScrollPane.setBounds(10,10, 140, 80); frame.getContentPane().add(myScrollPane); // second listbox app.myList2 = new JList(); app.myList2.setBounds(0,0,100,100); // make a scrollpane using this listbow JScrollPane myScrollPane2 = new JScrollPane(app.myList2); myScrollPane2.setBounds(230,10, 140, 80); frame.getContentPane().add(myScrollPane2); //add button app.addButton= new JButton("Add"); app.addButton.setBounds(10, 100, 100,20); frame.getContentPane().add(app.addButton); app.addButton.addActionListener(app); // add text field app.addText = new JTextField("Item to add"); app.addText.setBounds(130,100,100, 20); frame.getContentPane().add(app.addText); //delete button app.delButton= new JButton("Remove"); app.delButton.setBounds(10, 130, 100,20); frame.getContentPane().add(app.delButton); app.delButton.addActionListener(app); //copy button app.copyButton= new JButton(">>>"); app.copyButton.setBounds(160, 40, 60,20); frame.getContentPane().add(app.copyButton); app.copyButton.addActionListener(app); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { if (e.getSource()==addButton) { //copy text from text field and add to vector listContents.add(addText.getText()); myList1.setListData(listContents); } if (e.getSource()==delButton) { // get the indices of selected items int select[] = myList1.getSelectedIndices(); // copy these into a temporary vector Vector v = new Vector(); for (int i = 0; i<select.length; i++) { v.add((String)(myList1.getModel().getElementAt(select[i]))); } // remove from original vector for (int i=0; i<v.size(); i++) listContents.remove(v.elementAt(i)); // reset vector as list source myList1.setListData(listContents); } if (e.getSource()==copyButton) { // get the indices of selected items int select[] = myList1.getSelectedIndices(); // copy these into other vector vector2.clear(); // first empty it for (int i = 0; i<select.length; i++) { vector2.add((String)(myList1.getModel().getElementAt(select[i]))); } // reset data source myList2.setListData(vector2); } } public static void main(String[] args) { // start off.. try { UIManager.setLookAndFeel( "javax.swing.plaf.metal.MetalLookAndFeel" ); } catch (Exception e) { System.out.println("Cant get laf"); } SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JList myList1; JList myList2; JTextField addText; Vector listContents; Vector vector2; JButton addButton; JButton delButton; JButton copyButton; }
• #46: See next slide for examples
• #47: There are others - these are some common ones. Arguments for using layout managers are 1. Less code to write usually 2. Deals with the problem of differing screen resolutions meaning pixels vary in size 3. Deals with user resizing the window (layout manager rearranges things accordingly) Only problem is that it sometimes takes some ingenuity to get the layout you want.
• #48: Note there is no frame.setBounds to size the frame. Instead frame.pack() calculates the frame size to fit. FlowLayout just puts things in a row. If it runs out of room, it starts another row.
• #49: A BorderLayout divides the container into 5 parts - top bottom left right and center. Components are added to one of these parts, only one component per part. Panels default to borderlayout, so there is no .setLayout
• #50: A GridLayout is a rectangular array of locations. Items are added (by default) into top-down left-right order. In the GridLayout constructor - 1. The third and fourth arguments are gaps between cells. These default to 0 2. The first and second are rows and columns. Usually you supply just one of these (the other is zero). So if you had 0,3 you would get 3 columns, and the number of rows is determined by how many items are added. If you supply both, teh rows takes precedence.
• #51: Usually you would need to divide the main frame into several areas with different layoutmanagers. This is an example. Only the digit buttons do anything - I did not want to obscure using a layoumanager with the logic of writing a claculator. Font is a class. The constructor has 3 arguments - the font name, the style, and the point size. Source code import javax.swing.*; import java.awt.event.*; import java.awt.*; import java.util.*; public class Main implements ActionListener { private static void createAndShowGUI() { Main app = new Main(); JFrame.setDefaultLookAndFeelDecorated(true); // make frame JFrame frame = new JFrame("Calc"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().setLayout(null); frame.setBounds(50,50,190,170); // create top panel JPanel topPanel=new JPanel(); topPanel.setBounds(0,0, 200,28); topPanel.setLayout(null); // add display to it app.display.setBounds(0,0, 200,28); app.display.setBackground(Color.black); app.display.setForeground(Color.green); app.display.setFont(new Font("Palatino",Font.PLAIN,14)); topPanel.add(app.display); // show top panel frame.getContentPane().add(topPanel); // make lower panel JPanel lowerPanel=new JPanel(); frame.getContentPane().add(lowerPanel); lowerPanel.setBounds(0,32, 180,100); lowerPanel.setLayout(new GridLayout(0,4,2,2)); // add buttons to it app.add = new JButton("+"); lowerPanel.add(app.add); app.sub = new JButton("-"); lowerPanel.add(app.sub); app.mul = new JButton("X"); lowerPanel.add(app.mul); app.div = new JButton("/"); lowerPanel.add(app.div); for (int i=0; i<10; i++) { app.digits[i] = new JButton(""+i); app.digits[i].addActionListener(app); lowerPanel.add(app.digits[i]); } app.point = new JButton("."); lowerPanel.add(app.point); app.point.addActionListener(app); app.equals = new JButton("="); lowerPanel.add(app.equals); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { for (int i = 0; i<10; i++) { if (e.getSource()==digits[i]) current+=""+i; } if (e.getSource()==point) current+="."; display.setText(current); } public static void main(String[] args) { // start off.. try { UIManager.setLookAndFeel( "javax.swing.plaf.metal.MetalLookAndFeel" ); } catch (Exception e) { System.out.println("Cant get laf"); } SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields JButton add,sub, mul, div; JButton point, equals; JButton[] digits = new JButton[10]; String current = new String(); JTextField display = new JTextField(); }
• #52: So you make a menubar Make a menu (usually several) and add it to the bar Make menuitems and add them to a menu
• #53: MenuItems are like buttons and they use the ActionListener
• #54: This shows - 1. Menu item with an icon - in the constructor 2. A checkbox type item 3. A submenu added to a menu Source code import javax.swing.*; import java.awt.event.*; import java.awt.*; import java.util.*; public class Main implements ActionListener { private static void createAndShowGUI() { Main app = new Main(); JFrame.setDefaultLookAndFeelDecorated(true); // make frame JFrame frame = new JFrame("Menu things"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().setLayout(null); frame.setBounds(50,50,300,300); JMenuBar myMenuBar = new JMenuBar(); JMenu menu1 = new JMenu("File"); // item with an image JMenuItem itemgif = new JMenuItem("Gif option",new ImageIcon("icon.gif")); menu1.add(itemgif); // checkbox JCheckBoxMenuItem itemCheck = new JCheckBoxMenuItem("A check box menu item"); menu1.add(itemCheck); // submenu .. first make submenu JMenu subMenu = new JMenu("Sub..."); // add an item to it JMenuItem subMenuItem = new JMenuItem("An option"); subMenu.add(subMenuItem); // add it to main menu menu1.add(subMenu); JMenuItem item = new JMenuItem("Exit"); item.addActionListener(app); menu1.add(item); myMenuBar.add(menu1); frame.setJMenuBar(myMenuBar); frame.setVisible(true); } public void actionPerformed(ActionEvent e) { System.exit(0); } public static void main(String[] args) { // start off.. try { UIManager.setLookAndFeel( "javax.swing.plaf.metal.MetalLookAndFeel" ); } catch (Exception e) { System.out.println("Cant get laf"); } SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // application object fields }
• #55: A JToolBar holds a set of buttons - here all icons but could be text. If it is added to a container which is BorderLayout, it can be docked on a side, or left floating.