The JPasswordField
component is a child class of JTextField
and so has similar functionality, except that it masks the entered text with a character, the default
mask being '*'. Figure 12.9, “A Password Field Example” shows this example running. When the text is
entered (without being visible) the user can press the enter key and an ActionEvent
object will be generated. This ActionEvent
can be passed to the
actionPerformed()
method, where it can be identified and then the
password field can be interrogated using getPassword()
that returns an array
of char. The use of the char array is for security reasons and each
element of the array should be set to blank after the password has be validated. You can use the
setEchoChar('X')
to change the echo character to whatever is required.
The source code for this example is as below and as in
JPasswordFieldExample.java
1 2 3 // Swing JPasswordField Example - Derek Molloy 4 5 import javax.swing.*; 6 import java.awt.*; 7 import java.awt.event.*; 8 import javax.swing.border.*; 9 10 public class JPasswordFieldExample extends JFrame implements ActionListener 11 { 12 JLabel l1 = new JLabel("This is a Test Swing Application"); 13 JButton b1, b2; 14 JPasswordField pwd; 15 16 public JPasswordFieldExample() 17 { 18 super("JPassword Field Example"); 19 20 JPanel p = new JPanel(); 21 p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS)); 22 p.setBorder(new TitledBorder("Enter Your Password:")); 23 24 pwd = new JPasswordField(20); 25 pwd.addActionListener(this); 26 27 p.add(pwd); 28 this.getContentPane().add(p); 29 30 this.pack(); // set the size automatically 31 this.show(); // display the frame 32 } 33 34 public void actionPerformed(ActionEvent e) 35 { 36 if (e.getSource().equals(pwd)) 37 { 38 char[] thePassword = pwd.getPassword(); 39 String s = new String(thePassword); 40 System.out.println("Password is " + s); 41 } 42 } 43 44 public static void main(String[] args) 45 { 46 new JPasswordFieldExample(); 47 } 48 } 49 50
The JSlider
component is a replacement for the Scrollbar
AWT
component. It is mentioned here, because there is quite a range of new functionality available with this component.
For example if you look at the second JSlider
object from the top (the middle one)
in Figure 12.10, “A JSlider
Example”, you will see that it has a title, tick marks for intervals. The code
for this component is shown below:
1 2 3 // Code for the second slider from the top. 4 p = new JPanel(); 5 p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS)); 6 p.setBorder(new TitledBorder("Major Ticks")); 7 8 s = new JSlider(100, 1000, 400); 9 s.setPaintTicks(true); 10 s.setMajorTickSpacing(100); 11 s.getAccessibleContext().setAccessibleName("Major Ticks"); 12 s.getAccessibleContext().setAccessibleDescription("A slider showing major tick marks"); 13 s.addChangeListener(this); 14 p.add(s); 15 hp.add(p); 16 17
A JPanel
object is created for each JSlider
object. The
layout of this JPanel
object is set to BoxLayout
, which
allows multiple components to be laid out either vertically or horizontally, without wrapping. In this
case the components are laid out in BoxLayout.Y_AXIS
allowing the components to be laid
out vertically, and these components will remain vertical, even when the JFrame
is
resized. For a BoxLayout
you also have to pass the container that you wish to
lay out - in this case p
. TitleBorder
is another border that
you can use, that places a title around the border frame - in this case "Major Ticks"
.
The JSlider
object is then created with a minimum of 100, a maximum of 1000, and an
initial value of 400. The setPaintTicks()
enables/disables the tick lines below
the JSlider
component. The setMajorTickSpacing(100)
method
call sets spacing to 100, so we will have 10 ticks in this case.
The next two lines demonstrate the Accessibility API (part of the JFCs) that sets the Accessible name of this component to "Major Ticks" and the description to "A slider showing major tick marks", so that if the user has a visual disability that speech synthesis software would be capable of indentifying the reason for the component to allow that person to use it.
Other constructors that can be used with JSlider
are:
JSlider()
Creates a horizontal slider with the range 0 to 100 and an initial value of 50.JSlider(BoundedRangeModel brm)
Creates a horizontal slider using the specifiedBoundedRangeModel
. ABoundedRangeModel
defines the data model used by components like sliders and progressBars, four interrelated integer properties: minimum, maximum, extent and value. These four integers define two nested ranges like this: minimum <= value <= value+extent <= maximumJSlider(int orientation)
Creates a slider using the specified orientation with the range 0 to 100 and an initial value of 50.JSlider(int min, int max)
Creates a horizontal slider using the specified min and max with an initial value equal to the average of the min plus max.JSlider(int min, int max, int value)
Creates a horizontal slider using the specified min, max and value. The one used here.JSlider(int orientation, int min, int max, int value)
Creates a slider with the specified orientation and the specified minimum, maximum, and initial values.
The Full code for this example can be seen in
JSliderExample.java
A JProgressBar
component displays an Integer
value
within a bounded interval. A progress bar typically communicates the progress of an event by
displaying its percentage of completion and possibly also provides a textual description. See
Figure 12.11, “A JProgressBar
Example” for a basic example.
The code for this is in
JProgressBarExample.java
There are several constructors for JProgressBar
:
JProgressBar()
Creates a horizontal progress bar that displays a border but no progress string.JProgressBar(BoundedRangeModel newModel)
Creates a horizontal progress bar that uses the specified model to hold the progress bar's data.JProgressBar(int orient)
Creates a progress bar with the specified orientation, which can be either JProgressBar.VERTICAL or JProgressBar.HORIZONTAL.JProgressBar(int min, int max)
Creates a horizontal progress bar with the specified minimum and maximum.JProgressBar(int orient, int min, int max)
Creates a progress bar using the specified orientation, minimum, and maximum.
You can set the value of the progress bar by using the setValue(int)
method and you
can get the value by using the getValue()
method.
The JToggleButton
component is very similar to a checkbox, in that it can
be selected or not selected. Figure 12.12, “The JToggleButton
component example (a) selected (b) not selected.” shows a selected
JToggleButton
object and a non-selected component. It is very similar to the
JButton
class except that it can have two states.
The code for this example is in
JToggleButtonExample.java
There are several constructors for a JToggleButton
:
JToggleButton()
Creates an initially unselected toggle button without setting the text or image.JToggleButton(Action a)
Creates a toggle button where properties are taken from the Action supplied.JToggleButton(Icon icon)
Creates an initially unselected toggle button with the specified image but no text.JToggleButton(Icon icon, boolean selected)
Creates a toggle button with the specified image and selection state, but no text.JToggleButton(String text)
Creates an unselected toggle button with the specified text.JToggleButton(String text, boolean selected)
Creates a toggle button with the specified text and selection state.JToggleButton(String text, Icon icon)
Creates a toggle button that has the specified text and image, and that is initially unselected.JToggleButton(String text, Icon icon, boolean selected)
Creates a toggle button with the specified text, image, and selection state.
If you wish to find the current state of the JToggleButton
object using the
isSelected()
method that returns a boolean value.
Task: Write an egg timer Swing application that counts to two minutes (well
for runny eggs), updating the time as a progress bar and playing a sound when it is finished. You
should be able to stop the timer at any stage using the "stop" button. My version is in
Figure 12.13, “The Egg Timer Exercise”. You can use this sound
ready.wav
if you
wish.
Hints: Don't set the delay to 1 second until you have finished, otherwise you will have to wait a full two minutes every time you are debugging your application. To load a sound clip in an application you have to use something like:
1 2 3 File f = new File("ready.wav"); 4 AudioClip theSound; 5 try { 6 theSound = Applet.newAudioClip(f.toURL()); 7 } 8 catch (java.net.MalformedURLException e) { 9 theSound = null; 10 System.out.println("Exception " + e.toString()); 11 } 12 if (this.theSound != null) { 13 this.theSound.play(); 14 } 15 16
And this involves importing the java.applet.*
package and the
java.io.*
package. You may also (depending on the way you write your
code) have to add a sleep call after you call the play()
method of the
AudioClip
as the application/function may finish before the sound clip has
played completely.
Solution: My solution is here -
EggTimerApplication.java
.
Once again have a good attempt at the exercise before reading my solution (as yours may be better!).
© 2006
Dr. Derek Molloy
(DCU).