Using Objects Instead of Strings

• Though this method works, it is not ideal.
• We have a lot of logic that simply relates the Strings back to their original objects.
• Let's add the objects themselves instead.
• The list will display the results of the toString() method of the object.  (Corrected 4/23/2002. Changed the word return to display in the previous sentence for clarity.  The JList will return the object(s) themselves when getSelectedValues() is called, but will display, in the GUI, whatever the toString() method of that object returns.  Also made similar clarifications on the bullet point below.)
• By default, toString() returns the object name and attribute values.  It's not very intuitive.
• So, we'll need to override toString() with a more user-friendly implementation.
• Then, instead of sending the JList an array of Strings, we can send it an array of buildings.
• The look and feel is the same, only the source code has changed.
• Building
• Added the toString() overridden method that returns type, noted in green.

/**
 *
 * @author  default
 */
public class Building {

    String name;
    String function;

    /** Creates a new instance of Building */
    public Building(String name, String function) {
        this.name = name;
        this.function = function;

    }

    public void setName(String name) {
        this.name = name;
    }

    public void setFunction(String function) {
        this.function = function;
    }

    public String getFunction() {
        return function;
    }

    public String getName() {
        return name;
    }

    public String toString() {
        return name;
    }

}
 

• JListString is now JListObject.  Again, changed text noted in green.
• Note, I used Forte's GUI editor  to help me create this JFrame object and its components.  I did not do this by hand, and I recommend you use the GUI editor as well.

import javax.swing.*;

/**
 *
 * @author  default
 */
public class JListObject extends javax.swing.JFrame {

    Building[] buildings;

    /** Creates new form JListString */
    public JListObject() {
        initComponents();

        // Create a Buildings array.
        buildings = new Building[8];

        // Populate the array.
        buildings[0] = new Building("Sander", "CECE Computer Labs");
        buildings[1] = new Building("French", "CECE Administration");
        buildings[2] = new Building("Langsam", "Library");
        buildings[3] = new Building("Lindner", "College of Business Administration");
        buildings[4] = new Building("Tangeman", "Old University Center");
        buildings[5] = new Building("Tent City", "New University Center");
        buildings[6] = new Building("Shoemaker", "Arena");
        buildings[7] = new Building("Edwards", "Administration Center");

        // Send the buildings array to populate the JList, instead of the String array created earlier.
        lstBuildings.setListData(buildings);
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    private void initComponents() {
        scrBuildingList = new javax.swing.JScrollPane();
        lstBuildings = new javax.swing.JList();
        pnlButtons = new javax.swing.JPanel();
        btnShow = new javax.swing.JButton();
        lblTitle = new javax.swing.JLabel();

        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                exitForm(evt);
            }
        });

        scrBuildingList.setViewportView(lstBuildings);

        getContentPane().add(scrBuildingList, java.awt.BorderLayout.CENTER);

        btnShow.setText("Show");
        btnShow.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnShowActionPerformed(evt);
            }
        });

        pnlButtons.add(btnShow);

        getContentPane().add(pnlButtons, java.awt.BorderLayout.SOUTH);

        lblTitle.setText("Where have you been?");
        getContentPane().add(lblTitle, java.awt.BorderLayout.NORTH);

        pack();
    }

    private void btnShowActionPerformed(java.awt.event.ActionEvent evt) {

        //  get the selected buildings from the JList.
        Object[] selectedBuildings = lstBuildings.getSelectedValues();

        // Create a String that we will use to display an informative message to the user.
        String message = "Today you have been to the ";

        for (int i = 0; i < selectedBuildings.length; i++){
            if (i > 0) { message += ", "; }

            // Eliminate the for loop and if test.
            // Just get the Building object directly from the JList.
            Building building = (Building) selectedBuildings[i];
            message += building.getFunction();
        }

        JOptionPane.showMessageDialog(this, message, "Buildings Visited", JOptionPane.INFORMATION_MESSAGE);

    }

    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit(0);
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        new JListObject().show();
    }
 

    // Variables declaration - do not modify
    private javax.swing.JLabel lblTitle;
    private javax.swing.JList lstBuildings;
    private javax.swing.JPanel pnlButtons;
    private javax.swing.JScrollPane scrBuildingList;
    private javax.swing.JButton btnShow;
    // End of variables declaration

}
 

• This works fine for static lists.  But what about lists that change?  We need to look at ListModels.

Created by:  Brandan Jones December 17, 2001