Giving names to the columns in a JTable

Question

Hi,
I am using JTable(int numRows, int numColumns) constructor to create a JTable. After I built my application I came to knw that I cannot change the column names. The JTable in my GUI will keep on changing and the no. of rows,columns and even the column names may also change. I just wanted to know what constructor I should shift to.
Thanks,
Adhiraj

Answer 1

I would use something like the following:
DefaultTableModel model = new DefaultTableModel(columnNames, rowCount);
JTable table = new JTable( model );
The following code gives some examples on using the DefaultTableModel to add rows and columns:
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.table.*;
public class TableRowColumn extends JFrame
     private final static String LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
     JTable table;
     DefaultTableModel model;
     JPanel buttonPanel;
     JButton button;
     public TableRowColumn()
          //  Create table
          Object[][] data = { {"1", "A"}, {"2", "B"}, {"3", "C"} };
          String[] columnNames = {"Number","Letter"};
          model = new DefaultTableModel(data, columnNames);
          table = new JTable(model);
          table.putClientProperty("terminateEditOnFocusLost", Boolean.TRUE);
          //  Add table and a Button panel to the frame
          JScrollPane scrollPane = new JScrollPane( table );
          getContentPane().add( scrollPane );
          buttonPanel = new JPanel();
          getContentPane().add( buttonPanel, BorderLayout.SOUTH );
          button = new JButton( "Add Row" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    model.addRow( createRow() );
                    int row = table.getRowCount() - 1;
                    table.changeSelection(row, 0, false, false);
                    table.requestFocusInWindow();
          button = new JButton( "Insert Row" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    model.insertRow( 0, createRow() );
                    table.changeSelection(0, 0, false, false);
                    table.requestFocusInWindow();
          button = new JButton( "Empty Row" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    model.setRowCount( model.getRowCount() + 1 );
                    int row = table.getRowCount() - 1;
                    table.changeSelection(row, 0, false, false);
                    table.requestFocusInWindow();
          button = new JButton( "Add Column" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    String header = "Col" + (table.getColumnCount() + 1);
                    model.addColumn( header );
                    table.requestFocusInWindow();
          button = new JButton( "Add Column & Data" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    String header = "Col" + (table.getColumnCount() + 1);
                    int rows = table.getRowCount();
                    String[] values = new String[rows];
                    for (int j = 0; j < rows; j++)
                         values[j] = Integer.toString(j);
                    model.addColumn( header, values );
                    table.requestFocusInWindow();
          button = new JButton( "Add Column - No Reordering" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    //  Use this method when you don't want existing columns
                    //  to be rebuilt from the model.
                    //  (ie. moved columns will not be reordered)
                    table.setAutoCreateColumnsFromModel( false );
                    String header = "Col" + (table.getColumnCount() + 1);
                    model.addColumn( header );
                    //  AutoCreate is turned off so create table column here
                    TableColumn column = new TableColumn( table.getColumnCount() );
                    column.setHeaderValue( header );
                    table.addColumn( column );
                    // These won't work once setAutoCreate... has been set to false
                    buttonPanel.getComponent(3).setEnabled( false );
                    buttonPanel.getComponent(4).setEnabled( false );
                    table.requestFocusInWindow();
          button = new JButton( "Remove Last Column" );
          buttonPanel.add( button );
          button.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    int columns = model.getColumnCount();
                    if (columns > 0)
                         if (!table.getAutoCreateColumnsFromModel())
                              int view =
                                   table.convertColumnIndexToView(columns - 1);
                              TableColumn column =
                                   table.getColumnModel().getColumn(view);
                              table.getColumnModel().removeColumn( column );
                         model.setColumnCount(columns - 1);
                    table.requestFocusInWindow();
     private Object[] createRow()
          Object[] newRow = new Object[2];
          int row = table.getRowCount() + 1;
          newRow[0] = Integer.toString( row );
          newRow[1] = LETTERS.substring(row-1, row);
          return newRow;
     public static void main(String[] args)
          TableRowColumn frame = new TableRowColumn();
          frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
          frame.pack();
          frame.setLocationRelativeTo( null );
          frame.setVisible(true);
}