The Guidebook - Code Viewer

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

public class ComboBoxExample_Answer_1 implements   ActionListener{

    JComboBox colorChooser;
    // **** ANSWER ****
    // Instead of having 4 distinct panels
    // We create an array of them!
    JPanel [] panels = new JPanel[4];

    public JPanel createContentPane (){

        JPanel totalGUI = new JPanel();

        // To create a JComboBox, we need to pass in an array of Strings.
        // This gives the ComboBox the list of selections you can make.

        String colors[] = {"Red", "Blue", "Green", "Yellow"};

        colorChooser = new JComboBox(colors);
        colorChooser.setSelectedIndex(1);
        colorChooser.addActionListener(this);

        // Now we create a simple JPanel that displays our four coloured boxes.

        JPanel boxPanel = new JPanel(new GridLayout(2, 2, 20, 20));

        panels[0] = createSquareJPanel(Color.red, 50);
        panels[1] = createSquareJPanel(Color.blue, 50);
        panels[2] = createSquareJPanel(Color.green, 50);
        panels[3] = createSquareJPanel(Color.yellow, 50);

        // **** ANSWER ****
        // This sets all the panels to hidden, and adds them all to
        // the boxPanel using a for loop.
        // Then we set the blue panel to be shown.

        for(int i = 0; i < panels.length; i++)
        {
            panels[i].setVisible(false);
            boxPanel.add(panels[i]);
        }
        panels[1].setVisible(true);

        // This sets the widgets on the screen to be layed out in a
        // top to bottom fashion with spacers inbetween.

        JPanel bottomPanel = new JPanel();
        bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.PAGE_AXIS));

        bottomPanel.add(Box.createRigidArea(new Dimension(0,10)));
        bottomPanel.add(colorChooser);
        bottomPanel.add(Box.createRigidArea(new Dimension(0,20)));
        bottomPanel.add(boxPanel);
        bottomPanel.add(Box.createRigidArea(new Dimension(0,10)));

        totalGUI.add(bottomPanel);

        totalGUI.setOpaque(true);
        return totalGUI;
    }

    // In this method, we create a square JPanel of a colour and set size
    // specified by the arguments.

    private JPanel createSquareJPanel(Color color, int size) {
        JPanel tempPanel = new JPanel();
        tempPanel.setBackground(color);
        tempPanel.setMinimumSize(new Dimension(size, size));
        tempPanel.setMaximumSize(new Dimension(size, size));
        tempPanel.setPreferredSize(new Dimension(size, size));
        return tempPanel;
    }

    // This actionPerformed simply takes sets the visibility of each
    // coloured box depending on what is selected on the combo box.

    public void actionPerformed(ActionEvent e) {

        int temp;

        if(e.getSource() == colorChooser)
        {
            temp = colorChooser.getSelectedIndex();

            // **** ANSWER ****
            // Set all the panels to false
            // then the panel chosen to true!
            for(int i = 0; i < panels.length; i++)
            {
                panels[i].setVisible(false);
            }
            panels[temp].setVisible(true);   
        }
    }

    private static void createAndShowGUI() {

        JFrame.setDefaultLookAndFeelDecorated(true);
        JFrame frame = new JFrame("[=] JComboBox [=]");

        ComboBoxExample_Answer_1 demo = new ComboBoxExample_Answer_1();
        frame.setContentPane(demo.createContentPane());
        
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

// *************************************************************
// Name : ComboBoxExample_Answer_1.java
// Author : Stuart Davidson
// Date : 28/12/2006
// Description : Shows how an array can be used to store objects
// of the GUI to save time and space.
// *************************************************************