Adding Buttons inside cell of JTable along with data?

Yes, it is possible, although It won't be easy.

You have to write your own custom cell renderer and your own cell editor.

This is a sample I made in 5 minutes:

It is far from perfect, but shows the concept.

Here's the source code:

import java.awt.Component;
import java.awt.Font;
import javax.swing.*;
import javax.swing.table.*;
import java.awt.Dimension;

public class CustomCell {
    public static void main( String [] args ) { 
        Object [] columnNames = new Object[]{ "Id", "Quantity" };
        Object [][] data        = new Object[][]{ {"06", 1}, {"08", 2} };

        JTable table = new JTable( data, columnNames ) { 
            public TableCellRenderer getCellRenderer( int row, int column ) {
                return new PlusMinusCellRenderer();
            }
         };

        table.setRowHeight( 32 );
        showFrame( table );
    }

    private static void showFrame( JTable table ) {
        JFrame f = new JFrame("Custom Cell Renderer sample" );
        f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        f.add( new JScrollPane( table ) );
        f.pack();
        f.setVisible( true );
    }
}

class PlusMinusCellRenderer extends JPanel implements TableCellRenderer {
        public Component getTableCellRendererComponent(
                            final JTable table, Object value,
                            boolean isSelected, boolean hasFocus,
                            int row, int column) {
                this.add( new JTextField( value.toString()  ) );
                this.add( new JButton("+"));
                this.add( new JButton("-"));
                return this;
        }
}

Here's a thread that may be interesting and here.

As discussed in the tutorial you'll need both a renderer to display your value and an editor to detect events from the cell being edited. In this example, the Component is a JCheckBox. Note that this requires a custom DataModel that extends AbstractTableModel to supply the correct Class for a given column. Joonas' suggestion to use JSpinner is a good one that works well.

I think you need to create a custom cell renderer if you want to show anything else than text (or numbers) in the cell. The cell renderer's job is to paint whatever you need to show in the cell.

See Table Renderer documentation.

So in this case you could create a small JPane which contains the text field and the tiny + and - buttons - or a just a JSpinner component, if does what you need. A bit tricky, for sure, but should be possible.