This program shows you how to select some columns in the JTable programmatically. Below we demonstrates how to select columns using the setColumnSelectionInterval() method, remove or clear column selection using removeColumnSelectionInterval() method and use the addColumnSelectionInterval() to add more columns to the previously selected columns.

package org.kodejava.swing;

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

public class JTableColumnSelectProgrammatically extends JPanel {
    public JTableColumnSelectProgrammatically() {
        initializePanel();
    }

    public static void showFrame() {
        JPanel panel = new JTableColumnSelectProgrammatically();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTable Column Selection");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(JTableColumnSelectProgrammatically::showFrame);
    }

    private void initializePanel() {
        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(500, 500));

        final JTable table = new JTable(new MyTableModel());
        table.setFillsViewportHeight(true);
        JScrollPane pane = new JScrollPane(table);

        JLabel label1 = new JLabel("From col: ");
        final JTextField field1 = new JTextField(3);
        JLabel label2 = new JLabel("To col: ");
        final JTextField field2 = new JTextField(3);
        JButton select = new JButton("Select");
        JButton clear = new JButton("Clear");
        JButton add = new JButton("Add another one");

        // Enables column selection mode and disable row
        // selection mode.
        table.setColumnSelectionAllowed(true);
        table.setRowSelectionAllowed(false);

        // Select columns based on the input.
        select.addActionListener(event -> {
            int index1 = 0;
            int index2 = 0;
            try {
                index1 = Integer.parseInt(field1.getText());
                index2 = Integer.parseInt(field2.getText());
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }

            if (index1 <= 0 || index2 <= 0 ||
                    index1 > table.getColumnCount() ||
                    index2 > table.getColumnCount()) {
                JOptionPane.showMessageDialog(table, "Selection out of range!");
            } else {
                table.setColumnSelectionInterval(index1 - 1, index2 - 1);
            }
        });

        // Clears column selection
        clear.addActionListener(e -> {
            table.removeColumnSelectionInterval(0, table.getColumnCount() - 1);
            field1.setText("");
            field2.setText("");
        });

        // Add one more column after the last selected column.
        add.addActionListener(event -> {
            int index2 = 0;
            try {
                index2 = Integer.parseInt(field2.getText());
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }

            index2 = index2 + 1;
            if (index2 <= table.getColumnCount()) {
                table.addColumnSelectionInterval(index2 - 1, index2 - 1);
                field2.setText(String.valueOf(index2));
            }
        });

        JPanel command = new JPanel(new FlowLayout());
        command.add(label1);
        command.add(field1);
        command.add(label2);
        command.add(field2);
        command.add(select);
        command.add(clear);
        command.add(add);

        add(pane, BorderLayout.CENTER);
        add(command, BorderLayout.SOUTH);
    }

    public static class MyTableModel extends AbstractTableModel {
        private final String[] columns = {"ID", "NAME", "AGE", "A STUDENT?"};
        private final Object[][] data = {
                {1, "Alice", 20, Boolean.FALSE},
                {2, "Bob", 10, Boolean.TRUE},
                {3, "Carol", 15, Boolean.TRUE},
                {4, "Mallory", 25, Boolean.FALSE}
        };

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

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

        public Object getValueAt(int rowIndex, int columnIndex) {
            return data[rowIndex][columnIndex];
        }

        @Override
        public String getColumnName(int column) {
            return columns[column];
        }

        // This method is used by the JTable to define the default
        // renderer or editor for each cell. For example if you have
        // a boolean data it will be rendered as a checkbox. A
        // number value is right aligned.
        @Override
        public Class<?> getColumnClass(int columnIndex) {
            return data[0][columnIndex].getClass();
        }
    }

}

Below is the screen capture of the program.

Programmatically Select JTable Column

To right-align numbers type of data in JTable cells we need to implements a TableModel. The TableModel‘s interface getColumnClass(int index) implementation return the class of the cell values, this information is used by JTable component to setup a default renderer and editor for the column.

package org.kodejava.swing;

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

public class JTableNumberRightAlign extends JPanel {
    public JTableNumberRightAlign() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new JTableNumberRightAlign();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTable Number Align");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(JTableNumberRightAlign::showFrame);
    }

    private void initializeUI() {
        setLayout(new BorderLayout());
        setPreferredSize(new Dimension(500, 500));

        JTable table = new JTable(new NumberTableModel());
        table.setFillsViewportHeight(true);

        JScrollPane pane = new JScrollPane(table);
        add(pane, BorderLayout.CENTER);
    }

    static class NumberTableModel extends AbstractTableModel {
        String[] columns = {"STUDENT ID", "NAME", "YEARS", "SCORE"};
        Object[][] data = {
                {"S001", "ALICE", 10, 8.75},
                {"S002", "BOB", 10, 7.50},
                {"S003", "CAROL", 10, 9.00},
                {"S004", "MALLORY", 10, 8.50}
        };

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

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

        @Override
        public String getColumnName(int column) {
            return columns[column];
        }

        public Object getValueAt(int rowIndex, int columnIndex) {
            return data[rowIndex][columnIndex];
        }

        // This method is used by the JTable to define the default
        // renderer or editor for each cell. For example if you have
        // a boolean data it will be rendered as a checkbox. A
        // number value is right aligned.
        @Override
        public Class<?> getColumnClass(int columnIndex) {
            return data[0][columnIndex].getClass();
        }
    }
}

Here is the result of the program:

JTable Number Right Align