• Components/Widgets:
  • The parts of a GUI (e.g., buttons, sliders, text fields)
• Containers:
  • "Screen real estate" that contains components/widgets

• JFrame :
  • A main "window" most commonly used by an application
• JDialog :
  • A "child" window that is usually used for input/output

javaexamples/gui/JFrameDriver.java

import java.awt.*;
import javax.swing.*;


/**
 * An example that uses a JFrame
 *
 * @version 1.0
 * @author  Prof. David Bernstein, James Madison Univeristy
 */
public class JFrameDriver
{

    /**
     * The entry point of the example
     *
     * @param args   The command line arguments
     */
    public static void main(String[] args)
    {
        JFrame   f;


        f = new JFrame();
        f.setSize(400,400);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        
        f.setVisible(true);
    }
}
        

• The JRootPane :
  • RootPaneContainer objects have a JRootPane that manages layers (if any), menus (if any), and content
  • Generally should not be used
• The Content Pane:
  • A JRootPane has a Container called the content pane that manages all of the usable "screen real estate"
  • Accessed using the getContentPane() method

• JButton :
  • 
• JCheckBox /JRadioButton :
  • 
• JTextField /JTextArea :
  • 
• JComboBox :
  • 
• JSlider :
  • 

• Organizing GUI components
• Grouping GUI components
• Positioning GUI components

The null LayoutManager

javaexamples/layout/NullLayoutDriver.java

import java.awt.*;
import javax.swing.*;


/**
 * An example of absolute layout with the null layout manager
 *
 * @version 1.0
 * @author  Prof. David Bernstein, James Madison Univeristy
 */
public class NullLayoutDriver
{

    /**
     * The entry point of the example
     *
     * @param args   The command line arguments
     */
    public static void main(String[] args)
    {
        Container   contentPane;
        JButton     cancelButton, okButton;
        JFrame      frame;        
        JLabel      titleLabel;

        frame = new JFrame("A Really Amazing Window!");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       
        contentPane = frame.getContentPane();
        contentPane.setLayout(null);

        titleLabel = new JLabel("An Example of Absolute Layout");
        contentPane.add(titleLabel);
        titleLabel.setBounds(60,20,290,30);

        okButton = new JButton("OK");
        contentPane.add(okButton);
        okButton.setBounds(190,210,60,30);

        cancelButton = new JButton("Cancel");
        contentPane.add(cancelButton);
        cancelButton.setBounds(260,210,90,30);

        
        frame.setSize(400,400);
        frame.setVisible(true);
    }
}
        

• Relative Layout:
  • Components are positioned relative to each other, rather than an absolute position
• Template Layout:
  • Divide the container into sections and place one component in each section
• Hierarchical Template Layout:
  • Subdivide the sections in a template layout
• Constrained Template Layout:
  • Add constraints (e.g., doesn't expand) to sections of a template

1. Determine what events the component generates
2. Identify the interfaces that needs to be implemented
3. Create a class that implements that interfaces
4. Add "application logic" to the appropriate methods

• The Event(s):
  • ActionEvent
• The Interface(s):
  • ActionListener
• The Method(s)/Message(s):
  • void actionPerformed(ActionEvent event)

javaexamples/usinggui/ButtonHandler.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/**
 * An example that uses buttons
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class ButtonHandler implements ActionListener
{
    private JLabel outputLabel;
    

    /**
     * Ecplicit Value Constructor.
     */
    public ButtonHandler(JLabel outputLabel)
    {
        this.outputLabel = outputLabel;
    }


    /**
     * Handle actionPerformed message (required by ActionListener)
     *
     * @param event   The ActionEvent that generatedt his message
     */
    public void actionPerformed(ActionEvent event)
    {
       String       command;
       
       command = event.getActionCommand();
       if (command.equals("No"))
       {
          outputLabel.setText("Don't disagree with me!");
       }
       else if (command.equals("Yes"))
       {
          outputLabel.setText("I really respect your opinion.");
       }
    }
    
}
        

• JMenuBar:
  • Construct an empty JMenuBar object and then call its void add(JMenuItem item) method
  • JFrame has a void setJMenuBar(JMenuBar bar) method
• Parts of a Menu:
  • 

• The Idea:
  • Use a "viewport" to make only a portion of their total area visible at a time
  • Enable the visible portion to change (i.e., appear to scroll)
• In Java:
  • The Scrollable interface
  • A JScrollPane controls a Scrollable

• The Concept:
  • A container that can be repositioned
• In Java:
  • JToolBar

• Motivation:
  • Visually group components (e.g., a group of RadioButton objects)
• In Java:
  • A Border can be applied to any JComponent
  • Because a large number are used they should be created using a BorderFactory

• Use the same "screen real estate" for multiple purposes
• Put the different purposes on top of each other and provide a mechanism for moving between them
• In Java use the JTabbedPane