DefaultTableModel model=(DefaultTableModel)dbTbl.getModel();
try{
    Class.forName("com.mysql.jdbc.Driver");
    Connection con=DriverManager.getConnection("jdbc:mysql//localhost/:3306","root","password");
    Statement stmt=con.createStatement();
    ResultSet rs=stmt.executeQuery("show databases;");
    while(rs.next())
   {
    String db=rs.getString(1);
    model.addRow(new Object[] {db});
   }
    rs.close();
    stmt.close();
    con.close();
}
catch(Exception e)
{
    JOptionPane.showMessageDialog(null,"nahi chalda");
}

DefaultTableModel model = (DefaultTableModel) dbTbl.getModel();
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/:3306","root","password");
DatabaseMetaData meta = con.getMetaData();
ResultSet res = meta.getCatalogs();
while (res.next()) {
   String db = res.getString("TABLE_CAT");
   model.addRow(new Object[] {db});
}
res.close();

Connection con=DriverManager.getConnection("jdbc:mysql://localhost/:3306","root","password");