Question

我在我的java程序中创建了以下单例设计模式

      private int OwnerId;
    private String OwnerName;
    private String OwnerNic;
    private String OwnerAddress;
    private int OwnerTele;
    private String OwnerEmail;
    private String OwnerDate;


   private static OwnerML instance = new OwnerML();


    // make the coosntructor private so that this class cannot be instantiated
    private OwnerML(){}
     // get the only object available

   public static OwnerML getInstance() {
        return instance;
    }



    public int getOwnerId() {
        return OwnerId;
    }

    public void setOwnerId(int OwnerId) {
        this.OwnerId = OwnerId;
    }

我使用了一个单独的方法来调用view方法

   public ArrayList<OwnerML> SelectOwnerData()
{

    ArrayList<OwnerML> OwnerList = new ArrayList<OwnerML>();
   try {
       Connection con = DB.connect();
       String selectQ = "select * from owners";
       PreparedStatement ps2 = con.prepareStatement(selectQ);
       ResultSet rs = ps2.executeQuery();


        while (rs.next()) 
        {
            OwnerML OwnerData =OwnerML.getInstance();
            OwnerData.setOwnerId(rs.getInt(1));
            OwnerData.setOwnerName(rs.getString(2));
            OwnerData.setOwnerNic(rs.getString(3));
            OwnerData.setOwnerAddress(rs.getString(4));
            OwnerData.setOwnerTele(rs.getInt(5));     
            OwnerData.setOwnerEmail(rs.getString(6));  
            OwnerList.add(OwnerData);

        }
        rs.close();
       ps2.close();
       con.close();

通过使用以下方法，我在我的界面中调用它

 ArrayList<OwnerML> ownerList = new OwnerCL().SelectOwnerData();

    Object obj[][] = new Object[ownerList.size()][6];
    int x = 0;
    for (OwnerML t : ownerList) {

        obj[x][0] = t.getOwnerId();
        obj[x][1] = t.getOwnerName();
        obj[x][2] = t.getOwnerNic();
        obj[x][3] = t.getOwnerAddress();
        obj[x][4] = t.getOwnerTele();
        obj[x][5] = t.getOwnerEmail();
        x++;
    }
        ownerTbl.setModel(new javax.swing.table.DefaultTableModel(obj,new Object[]{

        "OwneID", "Name", "Nic", "Address", "Tele", "Email", "Date", "VehicleID", "Type", "Model", "Year", "RegNumber"
    }));

我目前面临的问题是它总是重复最后一行中的数据。如果有人能帮助我，我会非常感激。

Answer 1

您的设计中存在一个市长缺陷。我猜OwnerML类应该是数据的容器。将它作为Singleton实现是没有意义的。

每当您使用数据库中的结果填充OwnerML.getInstance()列表时调用OwnerList，您就会引用相同的类＆＃39;实例（这是Singleton的本质）因此，您将始终拥有一个列表，其中包含对同一对象的多个引用（单例）。

您应该忘记使用Singleton作为数据容器（让我们称之为数据传输对象 - DTO）。事实上，Singleton很少用于任何事情（特别是例外：日志子系统，单一硬件资源的处理程序，也许是Spring-ish bean工厂）。

简而言之：将OwnerML构造函数设为public，然后替换为 OwnerML OwnerData =OwnerML.getInstance();
与
OwnerML OwnerData = new OwnerML();

=== EDIT ===

@Anton的评论是第一次，他是对的。我下次应该打字更快：）

使用Java中的单一模式填充表

1 个答案: