Transcript Objects First With Java

GUI: Graphical User Interface
AWT/SWING:
Components
Drag and Drop in NetBeans
Events
Listeners
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Components
• GUIs are build using standard
components, for instance:
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–
–
–
–
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Windows (Frames in Java)
Menu bars
Text fields
List boxes
Buttons
Etc.
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Java.awt and javax.swing
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Some AWT and Swing Classes
java.lang.Object
java.awt.Component
java.awt.Container
Note the use
of inheritance
javax.swing.JComponent
java.awt.Window
javax.swing.JPanel
javax.swing.JFileChooser
java.awt.Frame
javax.swing.JPopupMenu
javax.swing.JToolbar
javax.swing.JFrame
javax.swing.JLabel
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Graphical User Interfaces
• A Graphical User Interface (GUI) is created
with at least three kinds of objects
– components
– events
– Listeners
• Java standard class library provides these
objects for us
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Components and Containers
• A GUI component defines a screen
element to display information or allow the
user to interact with the program
– buttons, text fields, labels, menus, etc.
• A container is a special component that
holds and organizes other components
– dialog boxes, applets, frames, panels, etc.
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Hello World Example
import javax.swing.*;
public class HelloWorldSwing {
public static void main(String[] args) {
JFrame frame = new JFrame("HelloWorldSwing");
JLabel label = new JLabel("Hello World");
frame.getContentPane().add(label);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200,200);
frame.setVisible(true);
}
}
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Frame
• The main component is a frame.
• Frame is the Java term for what is generally called a
‘window’.
• In Swing frames are realised by the class JFrame
• A frame is a rectangular area:
– title bar at the top
– The title bar contains buttons for closing, maximizing and
minimizing of the frame
– Below the title bare is an area at which further graphical
components can be placed
– This area is divided into two parts:
• space for a menu bar at the upper edge
• content pane below
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Elements of a JFrame
Title
Window controls
Menu bar
Content pane
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import java.awt.*;
import javax.swing.*;
Import
libraries
public class FirstFrame extends JFrame
{
public FirstFrame()
{
super("My First Frame");
setSize(200,200);
setVisible(true);
}
Inherit
JFrame
}
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import java.awt.*;
import javax.swing.*;
public class SecondFrame extends JFrame{
//Components neede to build the menubar
private JMenuBar menuBar;
private JMenu fileMenu, editMenu;
private JMenuItem openItem, quitItem;
public SecondFrame() {
super("My Second Frame");
buildMenu();
setSize(200,200);
setVisible(true);
}
private void buildMenu(){
menuBar = new JMenuBar();
fileMenu = new JMenu("File");
editMenu = new JMenu("Edit");
menuBar.add(fileMenu);
menuBar.add(editMenu);
openItem = new JMenuItem("Open");
quitItem = new JMenuItem("Quit");
fileMenu.add(openItem);
fileMenu.add(quitItem);
this.setJMenuBar(menuBar);
}
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private void buildInputpart(){
panelIO = new JPanel();
panelIO.setLayout(null);
labFirstName = new JLabel("First Name:");
labLastName = new JLabel("Last Name: ");
txtFirstName = new JTextField();
txtFirstName.setToolTipText("Input first name");
txtLastName = new JTextField();
txtLastName.setToolTipText("Input last name");
addComponent(panelIO, labFirstName, 20,20,70,20);
addComponent(panelIO, txtFirstName, 100,20,150,20);
addComponent(panelIO, labLastName, 20,45,70,20);
addComponent(panelIO, txtLastName, 100,45,150,20);
this.add(panelIO);
} void buildButtonpart(){
private
panelButton = new JPanel();
panelButton.setLayout(null);
submitBut = new JButton("Submit");
clearBut = new JButton("Clear");
addComponent(panelButton, submitBut, 20,80, 100,20);
addComponent(panelButton, clearBut, 130,80, 100,20);
this.add(panelButton);
}
private void addComponent(Container container,
Component c,int x,int y,int width,int height){
c.setBounds(x,y,width, height);
container.add(c);
}
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This is unbearable!
• Instead an IDE supporting Drag and Drop
• For instance NetBeans:
GUI Building in NetBeans IDE 5.0
or
http://www.netbeans.org/kb/55/quickstart-gui.html
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Creating a GUI Project
1. Choose File > New Project. Alternately, you can click the New Project icon
in the IDE toolbar.
2. In the Categories pane, select the General node and in the Projects pane,
choose Java Application. Click Next.
3. Enter ContactEditor in the Project Name field and specify the project
location.
4. Ensure that the Set as Main Project checkbox is selected and deselect
Create Main Class if it is selected.
5. Click Finish.
The IDE creates the ContactEditor folder on your system in the designated
location. This folder contains all of the project's associated files, including its
Ant script, folders for storing sources and tests, and a folder for projectspecific metadata. To view the project structure, use the IDE's Files window.
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Adding a Main Component
To create a JFrame container:
1. In the Projects window, right-click the ContactEditor node and
choose New > JFrame Form.
2. Enter ContactEditorUI as the Class Name.
3. Enter my.contacteditor as the package.
4. Click Finish. The IDE creates the ContactEditorUI form and the
ContactEditorUI class within the ContactEditorUI.java application
and opens the ContactEditorUI form in the GUI Builder. Notice that
the my.contacteditor package replaces the default package.
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Event Driven
• Programs with graphical user interfaces (GUIs)
are event driven:
– the program reacts to actions of the user
– these actions generate (‘fire’) events
– examples of events are:
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•
•
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pressing a key
moving the mouse
clicking on a button
selecting a menu item
– Components that reacts to events are called Listeners
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Eventhandling
Listener
React to the events
User interface
GUI Components fires the event
in response to being clicked
Java code
Components
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Hello World –
now with buttons!
Called when the
event occurs
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
jTextField1.setText("Hello World!");
}
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
System.exit(0);
}
We write the body of
the event handler
jButton1.setText("Say Hello");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
});
Listener
generated by
NetBeans
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Do it!
The tutorial: Adding Functionality to Buttons: A Beginners Guide
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