Java Swing | extend AbstractTableModel and use it with JTable | several questions

Question

I followed Oracle's model for implementing an AbstractTableModel

http://download.oracle.com/javase/tutorial/uiswing/examples/components/TableDemoProject/src/components/TableDemo.java

I did this because my table has to contain 3 columns, and the first has to be a JCheckBox.

Here's my code:

public class FestplattenreinigerGraphicalUserInterfaceHomePagePanelTableModel extends AbstractTableModel {
private String[] columnNames = {"Auswahl",
                                    "Dateiname",
                                    "Pfad"};
    private Object[][] data = {
    {new Boolean(true), "datei.tmp",
     "/home/user/tmp"}
    };

    public int getColumnCount() {
        return columnNames.length;
    }

    public int getRowCount() {
        return data.length;
    }

    public String getColumnName(int col) {
        return columnNames[col];
    }

    public Object getValueAt(int row, int col) {
        return data[row][col];
    }

    public Class getColumnClass(int c) {
        return getValueAt(0, c).getClass();
    }

     public boolean isCellEditable(int row, int col) {
        if (col == 0) {
            return true;
        } else {
            return false;
        }
    }

     public void setValueAt(Object value, int row, int col) {            
        data[row][col] = value;
        fireTableCellUpdated(row, col);
    }

}

Here are my questions:

1. How does JTable ( new JTable(FestplattenreinigerGraphicalUserInterfaceHomePagePanelTableModel) ) know what the column names are and their values are? Since there's no contructor in my AbstractTableModel?! Is it becaue columnNames and data must be named like they are and JTable accesses them?
2. How can i put new Values in my JTable? Since columnNames and data are arrays. Can i replace them with vectors? If so, how do I init these vectors? In a constructor in myAbsTableModel?

I think it's very easy to get a solution but this Table handling isn't trivial to me, so thank u very much!

Answer 1

All Swing components come with default model implementations. I suggest you understand how to use them first before trying to create your own. For a JTable its called the DefaultTableModel. Read the API for methods to dynamically add/remove rows of data from the model. Here is a simple example to get you started:

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

public class TableBasic extends JPanel
{
    public TableBasic()
    {
        String[] columnNames = {"Date", "String", "Integer", "Boolean"};

        Object[][] data =
        {
            {new Date(), "A", new Double(1), Boolean.TRUE },
            {new Date(), "B", new Double(2), Boolean.FALSE},
            {new Date(), "C", new Double(9), Boolean.TRUE },
            {new Date(), "D", new Double(4), Boolean.FALSE}
        };

        JTable table = new JTable(data, columnNames)
        {
            //  Returning the Class of each column will allow different
            //  renderers and editors to be used based on Class

            public Class getColumnClass(int column)
            {
                for (int row = 0; row < getRowCount(); row++)
                {
                    Object o = getValueAt(row, column);

                    if (o != null)
                        return o.getClass();
                }

                return Object.class;
            }
        };
        table.setPreferredScrollableViewportSize(table.getPreferredSize());
        JScrollPane scrollPane = new JScrollPane( table );
        add( scrollPane );
    }

    private static void createAndShowUI()
    {
        JFrame frame = new JFrame("TableBasic");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new TableBasic() );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

Answer 2

First, I think you need to learn a bit more about Java, especially inheritance (I'm referencing your constructor problem.

Answers to your questions :

• define your column names via a private final static attribute, assuming your column names don't change.
• since your class extends AbstractTableModel , you can define a constructor for it, where you'll pass the data. Redefine the getValueAt method to allow the model to use the data you're passing.

Some more advice :

• don't do what you're doing in getColumnClass . Normally, all elements in a column will have the same class, so do a switch on the column index to get the classes.
• to add a JCheckBox in one of your columns, you'll have to use a custom TableCellRenderer

Answer 3

1. The JTable determines how many columns by calling getColumnCount() on your column model. It then iterates and calls getColumnName(idx) for each column. Your class tells it the column name -- look at your implementation of those methods.

2. You can store your data in whatever format you want. The JTable calls methods on your table model to retrieve that data. If you want to add new items to your model, you can implement an addItem(Object o) method to your model; just be sure to call fireTableRowsInserted() for each new item.