The content below discusses material not explicitly covered in the above reference.
Few people code GUI's by hand these days--it's just too complicated. Typically, one would use a "GUI builder" to drag-and-drop GUI components onto a design canvas, greatly simplifying and speeding up the GUI creation process. But it is very helpful to know the basics of how to build a GUI by hand because one often needs to go in an manually tweak the GUI code even when using a sophisticated GUI builder tool.
Basic structure of a simple GUI application:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class MyGUIApp extends JFrame {
// Use fields for GUI components that need to be referenced outside of the GUI initialization process (initGUI)
/**
* Constructor for the GUI.
*/
public MyGUIApp() {
// initialize fields here. Surrounding your code in a protective try-catch is recommended.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Causes the application to end if the GUI frame is closed.
initGUI(); // initialize the GUI components
}
/**
* Actually start the GUI
*/
public void start() {
// Do any last second initializations, if needed.
setVisible(true); // Make the GUI visible
}
/**
* Initialize the GUI components
*/
private void initGUI() {
Container contentPane = getContentPane(); // all GUI components are added to the frame's ContentPane.
// You can also just call the accessor each time as well and not use a local variable.
// instantiate, initialize and connect all the GUI's components here.
// Don't forget to add them to the container that holds them, e.g. the ContentPane.
}
/**
* Main method that starts the app.
* In general, this would not be in this class but rather in a separate "controller" class
* with slightly different coding (as required for a true Model-View-Controller system).
* We put it here for now, for simplicity's sake only.
*/
public static void main(String[] args) {
// initialize and start the GUI on the GUI thread.
SwingUtilities.invokeLater(new Runnable() {
public void run() {
MyGUIApp view = new MyGUIApp(); // instantiate the GUI but don't show it yet.
// Model classes would be instantiated here plus any other required objects.
view.start(); // Start the application by making the GUI visible.
}
});
}
}
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Set title and size of the frame:
setTitle("My Incredible GUI App"); // set the frame's title
setSize(400, 300); // set frame size to 400x300
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Panels in main frame:
JPanel controlPnl = new JPanel(); controlPnl.setBackground(Color.BLUE); // Set panel color to blue contentPane.add(controlPnl, BorderLayout.NORTH); // Fixed-size panel for control components, e.g. buttons, textfields, etc, at the top of the frame. JPanel displayPnl = new JPanel(); contentPane.add(displayPnl, BorderLayout.CENTER); // Adjustable-size panel for display components, e.g. text areas, etc, in the middle of the frame. |
A Button with a listener on the control panel:
JButton runBtn = new JButton("Run!");
runBtn.addActionListener(new ActionListener() {
/**
* This method runs when the button is clicked.
*/
public void actionPerformed(ActionEvent evt) {
// Do stuff here. Generally, delegate to a non-GUI object (the "model").
}
});
controlPnl.add(runBtn);
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A Label and a TextField with a listener on the control panel:
JLabel infoLbl = new JLabel();
infoLbl.setText("Enter text here:");
controlPnl.add(infoLbl);
final JTextField infoTF = new JTextField("default text"); // don't need "final" below if this line was defining a field instead of a local variable.
infoTF.setPreferredSize(new java.awt.Dimension(75, 23)); // set default text field size to 75x23 pixels.
infoTF.addActionListener(new ActionListener() {
/**
* This method runs when "Enter" is pressed after entering text into the text field.
*/
public void actionPerformed(ActionEvent evt) {
String text = infoTF.getText(); // the text of the text field.
// Do stuff here. Generally, delegate to a non-GUI object (the "model").
}
});
controlPnl.add(infoTF);
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A text area with scroll bars in the center of the frame:
JScrollPane scrollPn = new JScrollPane();
contentPane.add(scrollPn, BorderLayout.CENTER); // No center panel needed. ScrollPane added directly to frame.
JTextArea displayTA = new JTextArea("initial text");
scrollPn.setViewportView(displayTA); // put the text area in the scroll pane
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A very common compiler warning to receive is the following for your frame class and other customized GUI components:
The serializable class XXX does not declare a static final serialVersionUID field of type long |
If you do, add the following field to the class:
private static final long serialVersionUID = 42L; // Use a random, unique integer value here |
For more information, see this web page .