How to center in JTable cell a value?

You need to customize the renderer. To center the first column you can do:

DefaultTableCellRenderer centerRenderer = new DefaultTableCellRenderer();
centerRenderer.setHorizontalAlignment( JLabel.CENTER );
table.getColumnModel().getColumn(0).setCellRenderer( centerRenderer );

To center all columns with String data you can do:

DefaultTableCellRenderer centerRenderer = new DefaultTableCellRenderer();
centerRenderer.setHorizontalAlignment( JLabel.CENTER );
table.setDefaultRenderer(String.class, centerRenderer);