add value at col,row in a 2d arraylist

[Matt Kurz]

Hello.

MyTableModel model = new MyTableModel();
model.setValueAt("hello", 1, 1);
    

throws

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 1, Size: 0
at java.util.ArrayList.add(ArrayList.java:367)
at tableModelDemo.MyTableModel.setValueAt(MyTableModel.java:80)
at tableModelDemo.TableDemo.<init>(TableDemo.java:35)
at tableModelDemo.TableDemo.createAndShowGUI(TableDemo.java:57)
at tableModelDemo.TableDemo.access$0(TableDemo.java:48)
at tableModelDemo.TableDemo$1.run(TableDemo.java:71)

I don't see the error. Please help. Here is the class with the relevant methods:

class MyTableModel extends AbstractTableModel {
    int i = 0;
    
    private ArrayList<String> columnNames = new ArrayList<String>();
    
    //2d arraylist
    ArrayList<ArrayList<Object>> content2Darray = new ArrayList<ArrayList<Object>>();

    // constructor
    public MyTableModel(){

    }

    public int getColumnCount() {
      return columnNames.size(); 
    }

    public int getRowCount() {
      return content2Darray.size();
    }

    public String getColumnName(int col) {
        return columnNames.get(col);
    }

    public Object getValueAt(int row, int col) {
      return content2Darray.get(row).get(col);
    }

    public void addColumn() {
        i++;
        String s = String.valueOf(i);
        columnNames.add(s + "xxxxxx");
        fireTableStructureChanged();
    }
    
    /*
     * JTable uses this method to determine the default renderer/ editor for
     * each cell. If we didn't implement this method, then the last column
     * would contain text ("true"/"false"), rather than a check box.
     */
    public Class getColumnClass(int c) {
      return getValueAt(0, c).getClass();
    }

    /*
     * Don't need to implement this method unless your table's editable.
     */
    public boolean isCellEditable(int row, int col) {
      //Note that the data/cell address is constant,
      //no matter where the cell appears onscreen.
      if (col < 2) {
        return false;
      } else {
        return true;
      }
    }

    /*
     * Don't need to implement this method unless your table's data can
     * change.
     */
    public void setValueAt(Object data, int row, int col) {
      ensureCapacity(row, col);
      content2Darray.get(row).add(col, data);
      fireTableCellUpdated(row, col);
    }

    public void ensureCapacity(int row)
    {
         while (row >= content2Darray.size())
         {
             content2Darray.add(new ArrayList<Object>());
             fireTableStructureChanged();
         }
    }

    public void ensureCapacity(int row, int num)
    {
         ensureCapacity(row);
         content2Darray.get(row).ensureCapacity(num);
    }
  }    

[Christophe Verré]

First, you have no elements in your array. Then you try to set the 1st element. You check that the size is big enough. It's not. So you add a new element to the array. The problem is that the first element index is 0, and you are trying to access it with the "row" which is 1. Shouldn't you do model.setValueAt("hello", 0, 0); instead ? (or correct ensureCapacity to make enough rows (i.e. looping from content2Darray.size() to row included))

[Rob Spoor]

You're ensuring that there is an ArrayList for the row, but not that there are enough elements in this row. Yes, you are calling content2Darray.get(row).ensureCapacity(num), but that only makes sure there is room in the backing array to store enough elements without needing to resize (and frankly, 1 too few; col == 1 means there must be space for two elements). It doesn't change the size, or add elements.

I'd change it slightly:

    public void ensureCapacity(int row, int num) // num is col + 1 so the actual desired size of the row
    {
         ensureCapacity(row);
         ArrayList<Object> list = content2Darray.get(row);
         list.ensureCapacity(num);
         while (list.size() < num)
         {
             list.add(null);
         }
    }

    public void setValueAt(Object data, int row, int col) {
      ensureCapacity(row, col + 1); // column 1 needs room for two elements
      System.out.println(content2Darray);
      System.out.println(content2Darray.get(row));
      content2Darray.get(row).set(col, data); // overwrite, don't add
      fireTableCellUpdated(row, col);
    }

Two final notes:
- you forgot the fireTableStructureChanged() call in ensureCapacity(row, num)
- either call fireTableStructureChanged() once, at the end (and only if needed), or call the proper method: fireTableRowsInserted

There are still other problems here though: getValueAt may also throw exceptions, because you may be trying to access elements that do not exist. Here too you must call ensureCapacity(row, col + 1) first.

[Matt Kurz]

Hello.

First: Thanks for your help. I have still some questions.

Rob Prime wrote:
col == 1 means there must be space for two elements). It doesn't change the size, or add elements.

Why?
You mean this code line:

ensureCapacity(row, col + 1); // column 1 needs room for two elements    

Rob Prime wrote:
- you forgot the fireTableStructureChanged() call in ensureCapacity(row, num)

I tried several variations, without succes. The table is always empty.

Rob Prime wrote:
- either call fireTableStructureChanged() once, at the end (and only if needed), or call the proper method: fireTableRowsInserted

How can I do it only if needed?

Rob Prime wrote:
There are still other problems here though: getValueAt may also throw exceptions, because you may be trying to access elements that do not exist. Here too you must call ensureCapacity(row, col + 1) first.

Ok. I prefer to check for existance.


Does somebody have a complete example for a TableModel with a 2d ArraylList? It would help to see, how it's right. Or a good link with much help informations? I already know the SUN tutorial, but it ends, where I begin.

Here is a self running example of my current code:

package tableModelDemo;

import java.awt.Dimension;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;

public class TableDemo extends JPanel {

  public TableDemo() {
    super(new GridLayout(1, 0));

    MyTableModel model = new MyTableModel();
    JTable table = new JTable(model);
    table.setPreferredScrollableViewportSize(new Dimension(500, 70));

    JScrollPane scrollPane = new JScrollPane(table);
    add(scrollPane);
//    model.addColumn();
//    model.addColumn();
//    model.addColumn();

    model.setValueAt("hello", 2, 4);   // data, row, col    - array begins with index 0!
   
   System.out.println("VALUE AT 2,4: " + model.getValueAt(2, 4));
  }

  

  private static void createAndShowGUI() {
    JFrame.setDefaultLookAndFeelDecorated(true);
    JFrame frame = new JFrame("TableDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    TableDemo newContentPane = new TableDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}


package tableModelDemo;

import java.util.ArrayList;

import javax.swing.table.AbstractTableModel;

class MyTableModel extends AbstractTableModel {
    int i = 0;

    private ArrayList<String> columnNames = new ArrayList<String>();

    // 2d arraylist
    ArrayList<ArrayList<Object>> content2Darray = new ArrayList<ArrayList<Object>>();

    // constructor
    public MyTableModel() {

    }

    public int getColumnCount() {
        return columnNames.size();
    }

    public int getRowCount() {
        return content2Darray.size();
    }

    public String getColumnName(int col) {
        return columnNames.get(col);
    }

    public Object getValueAt(int row, int col) {
        return content2Darray.get(row).get(col);
    }

    public void addColumn() {
        i++;
        String s = String.valueOf(i);
        columnNames.add(s + "xxxxxx");
        fireTableStructureChanged();
    }

    /*
     * JTable uses this method to determine the default renderer/ editor for
     * each cell. If we didn't implement this method, then the last column would
     * contain text ("true"/"false"), rather than a check box.
     */
    public Class getColumnClass(int c) {
        return getValueAt(0, c).getClass();
    }

    /*
     * Don't need to implement this method unless your table's editable.
     */
    public boolean isCellEditable(int row, int col) {
        // Note that the data/cell address is constant,
        // no matter where the cell appears onscreen.
        if (col < 2) {
            return false;
        } else {
            return true;
        }
    }

    /*
     * Don't need to implement this method unless your table's data can change.
     */
    public void setValueAt(Object data, int row, int col) {
        ensureCapacity(row, col + 1); // column 1 needs room for two elements
        System.out.println("#" + content2Darray);
        System.out.println("#" + content2Darray.get(row));
        content2Darray.get(row).set(col, data); // overwrite, don't add
        fireTableCellUpdated(row, col);
        System.out.println("##" + content2Darray);
        System.out.println("##" +content2Darray.get(row));

    }

    public void ensureCapacity(int index) {
        while (index >= content2Darray.size()) {
            content2Darray.add(new ArrayList<Object>());
            fireTableDataChanged();
        }
    }

    public void ensureCapacity(int row, int num) // num is col + 1 so the actual
    // desired size of the row
    {
        ensureCapacity(row);
        ArrayList<Object> list = content2Darray.get(row);
        list.ensureCapacity(num);
        fireTableStructureChanged();
        while (list.size() < num) {
            list.add(null);
        }
        fireTableDataChanged();
    }
}

    

[pete stein]

It would make sense to me that you would first want to add columns (so your column count isn't 0) and rows (so your ArrayLists can accept data before setting values.

[Matt Kurz]

pete stein wrote:It would make sense to me that you would first want to add columns (so your column count isn't 0) and rows (so your ArrayLists can accept data before setting values.

I see what you mean. JTable is a beast!

Now I makes some steps back and try to learn with the DefaultTableModel. I made an experiment:

    DefaultTableModel model = new DefaultTableModel();
    // column model
    DefaultTableColumnModel cm = new DefaultTableColumnModel();
    // create jtable with table AND columnmodel
    JTable table = new JTable(model, cm);  

    TableColumn t1 = new TableColumn(0, 200);
    t1.setHeaderValue(44);   // geht noch nicht
    cm.addColumn(t1);
    model.fireTableStructureChanged();
    
    TableColumn t2 = new TableColumn(1, 400);
    t2.setHeaderValue("bbbb");
    System.out.println("column width is: " + t2.getWidth());
    cm.addColumn(t2);
    model.fireTableStructureChanged();

      model.setColumnCount(4);
     System.out.println("columnmodel says nr colums is: " + cm.getColumnCount());
     System.out.println("tablemodel says nr colums is : " + model.getColumnCount());
 

The Output is:
columnmodel says nr colums is: 2
tablemodel says nr colums is : 4

The Gui views 2 columns.
Intresting is, that If I use setValueAt(), I have to do something like model.setColumnCount(4) first. It's not enough to add the columns to the ColumnModel. It seems like the developer must care both, if he wants to use the methods provided by the TableModel. That's all, but not fine.