Activate JButton from selection in JTable and remove the initial focus from the table

To avoid automatic selection, you need to change the focus of the table when opening the window.

If your class inherits from JFrame :

this.requestFocus();

If you start a window from a variable:

meuFrame.requestFocus();

requestFocus() will change the focus to its main window, thus preventing JTable from appearing with the first line selected.

To activate the button only when there is a selection, try the below:

this.tabela.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
            @Override
            public void valueChanged(ListSelectionEvent e) {
                ListSelectionModel lsm = (ListSelectionModel) e.getSource();
                //altera os botoes para ativados somente se houver linha selecionada
                myButton.setEnabled(!lsm.isSelectionEmpty());
            }
        });

This way button activation is dependent on whether or not there is any selected field / row in the table.

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

class SelectTableExample
        extends     JFrame
        implements  ListSelectionListener
{
    // Instance attributes used in this example
   private  JPanel      topPanel;
   private  JTable      table;
   private  JScrollPane scrollPane;
   private  JButton     button;

    // Constructor of main frame
   public SelectTableExample()
   {
    // Set the frame characteristics
      setTitle( "Simple Table Application" );
      setSize( 300, 200 );
      setBackground( Color.gray );

    // Create a panel to hold all other components
      topPanel = new JPanel();
      topPanel.setLayout( new BorderLayout() );
      getContentPane().add( topPanel );

    // Create columns names
      String columnNames[] = { "Column 1", "Column 2", "Column 3" };

    // Create some data
      String dataValues[][] =
         {
         { "12", "234", "67" },
         { "-123", "43", "853" },
         { "93", "89.2", "109" },
         { "279", "9033", "3092" }
         };

    // Create a new table instance
      table = new JTable( dataValues, columnNames );

      // Block cell edition
      table.setModel(
            new DefaultTableModel(dataValues, columnNames) {
               public boolean isCellEditable(int row, int column) { 
                  return false;
               }
            });

        // Handle the listener
      ListSelectionModel selectionModel = table.getSelectionModel();
      selectionModel.addListSelectionListener( this );

    // Add the table to a scrolling pane
      scrollPane = new JScrollPane( table );
      topPanel.add( scrollPane, BorderLayout.CENTER );

      button = new JButton("continuar");
      button.setEnabled(false);
      topPanel.add( button, BorderLayout.SOUTH );
   }

    // Enable button for list selection changes
   public void valueChanged( ListSelectionEvent event )
   {
    // See if this is a valid table selection
      if( event.getSource() == table.getSelectionModel()
                    && event.getFirstIndex() >= 0 )
      {
         button.setEnabled(true);
      }
   }

    // Main entry point for this example
   public static void main( String args[] )
   {
    // Create an instance of the test application
      SelectTableExample mainFrame  = new SelectTableExample();
      mainFrame.setVisible( true );
   }
}