HOw can i assign a default action of Enter key after cell of jtable is edited to a Button???

Not sure this is what you want. Your question isn't very well explained.

public void actionPerformed(ActionEvent e) {

    if(e.getSource() == JTable()) {
        JButton.doClick();
    }
}

It seems that you are referring to a how to control the cell.

For this you will either have write your cell editor or override the DefaulCellEditor which is usually added to cells.

Add a keylistener to the editor component where you would be able to listen to the enterkey.

Try this out and if you are stuck midway would be happy to help :)