Question

（我不确定标题，因为我不知道如何清楚地表达我的想法）。

我有一个JTable。每次用户想要改变它的一些数据时，我都希望将旧数据保存在List中。然后我想做一些sql更新的东西，所以我想知道发生了更改的确切行。因此，我决定使用特定行作为键创建一个Map，使用旧数据创建一个列表（Map＆gt;）。

下面是我的代码

public class MapListsInJtable extends JFrame{
  private final Object[][] rowdata = { {"one",1}, {"two",2}, {"three",3}};
  private final Object[] colnames = {"col1", "col2", "col3"};
  private final List<Object> oldValues; //for updated list
  private final Map<Integer,List<Object>> updatedList;
  private DefaultTableModel model;
  private JTable table;
  private JScrollPane scrollPane;

  public MapListsInJtable(){
    this.updatedList = new Hashtable<>();
    this.oldValues = new ArrayList<>();
    initializeTable();
  }

  private void initializeTable(){
    model = new DefaultTableModel(rowdata,colnames);
    table = new JTable(model){

        @Override
        public void changeSelection(int rowIndex, int columnIndex, boolean toggle, boolean extend) {
            super.changeSelection(rowIndex, columnIndex, toggle, extend);
            if(toggle){
                //user gathers rows in order to delete them by holding ctrl
                System.out.println("toggling...");
                for(int i = 0; i < model.getColumnCount(); i++)
                    oldValues.add(table.getValueAt(rowIndex, i));
            }
            else{
                //user presses left mouse button and selects multiple rows
                if(extend){
                    System.out.println("extends...");
                    for(int i = 0; i < model.getColumnCount(); i++)
                        oldValues.add(table.getValueAt(rowIndex, i));
                }
                else{
                    oldValues.clear();
                }
            }
        }
    };
    //to see if there has been change in table data
    ListSelectionHandler handler = new ListSelectionHandler(this);
    table.getSelectionModel().addListSelectionListener(handler);

    table.setCellSelectionEnabled(false);
    table.setCellSelectionEnabled(false);
    table.setColumnSelectionAllowed(false);
    table.setRowSelectionAllowed(true);
    //resize columns and use horizontal scroll bar to view data
    table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
    //disable column dragging
    table.getTableHeader().setReorderingAllowed(false);
    scrollPane = new javax.swing.JScrollPane(table, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
}

protected DefaultTableModel getModel(){return model;}
public JTable getTable(){return table;}
public List<Object> getOldValues(){return this.oldValues;}
public Map<Integer,List<Object>> getUpdatedList(){return this.updatedList;}

public void initializeUI(){
    getContentPane().add(scrollPane);
    setSize(300,150);
    setVisible(true);
    setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
}

private class ListSelectionHandler implements ListSelectionListener{
    private final MapListsInJtable m;

    public ListSelectionHandler(MapListsInJtable m){this.m = m;}

    @Override
    public void valueChanged(ListSelectionEvent e) {
        //in order not valueChanged to be called twice
        boolean hasBeenAdjusted = e.getValueIsAdjusting();
        if(hasBeenAdjusted == true){
            int selectedRow = m.getTable().getSelectedRow();
            //put data in updatedList
            for(int i = 0; i < m.getModel().getColumnCount(); i++)
                m.getOldValues().add(m.getTable().getValueAt(selectedRow, i));
            m.getUpdatedList().put(selectedRow, m.getOldValues());
            System.out.println("updatedList: " + m.getUpdatedList());
          }
      }
  }

  public static void main(String[] af){
    MapListsInJtable m = new MapListsInJtable();
    m.initializeUI();
  }
}

当我选择一行时，数据通常放在updatedList中。

输出：

updatedList: {0=[`one, 1, null`]}

但是当我选择另一行时，我在updatedList中有2个位置和新行的数据。之前的所有数据都已消失。

输出：

updatedList: {1=[`two, 2, null`], 0=[`two, 2, null`]}

有人可以解释一下，为什么会这样？我该怎么办呢？提前谢谢

Answer 1

我认为这段代码就是问题：

  int selectedRow = m.getTable().getSelectedRow();
                //put data in updatedList
                for(int i = 0; i < m.getModel().getColumnCount(); i++)
                    m.getOldValues().add(m.getTable().getValueAt(selectedRow, i));
                m.getUpdatedList().put(selectedRow, m.getOldValues());
                System.out.println("updatedList: " + m.getUpdatedList());
              }

所以，试试这个：

  int selectedRow = m.getTable().getSelectedRow();
                //put data in updatedList
                for(int i = 0; i < m.getModel().getColumnCount(); i++)
                m.getOldValues().add(m.getTable().getValueAt(selectedRow, i));
                List oldvalue = ((List) ((ArrayList) m.getOldValues()).clone());
                m.getUpdatedList().put(selectedRow, oldvalue);
                System.out.println("updatedList: " + m.getUpdatedList());
              }

Java Map <integer，list <object>＆gt;不保存以前的数据</integer，list <object>

1 个答案: