Calculate sum in jtable and display the sum in jtextfield

[yesaya handoyo]

Hi all,i got a table that contains codes,names,qty,price and totals.What i want to ask is how to calculate the qty*price and the total was putted in the the totals column and also putted in the JTextField..When there are new rows,or deleted rows,it will automatically edited in the JTextField..Thanks a lot.

[Rob Spoor]

Add a TableModelListener to your JTable's model to listen for add / delete / change events. For the rest it's just iterating over your model:

for (int i = 0, rows = model.getRowCount(); i < rows; i++)
{
    total += model.getValueAt(i, X) * model.getValueAt(i, Y);
}

That loop body is pseudo code of course; you need to fill in X and Y to be your quantity and price columns, cast the the results of the getValueAt calls to whatever class you are storing, and retrieving the primitive from them. That part is quite trivial though.

May I add one suggestion though: float and double are not precise enough for money calculations. java.math.BigDecimal can be used instead. The loop body would become:

BigDecimal quantity = (BigDecimal)model.getValueAt(i, X);
BigDecimal price = (BigDecimal)model.getValueAt(i, Y);
total = total.add(quantity.multiply(price));

You could use Integer or Long for the quantity if you only want whole units, but then you would need to convert when calculating the total.

[yesaya handoyo]

Ok,thanks a lot..I'll try it..Anyway how to get the value for filling the x and y??Thanks..

[Rob Spoor]

Well you've specified those when creating your TableModel.
Suppose you've created it with headers "Column 1", "Column 2", "Price", "Column 4", "Quantity" and "Column 6", then X and Y are 2 and 4 (since indexing starts at 0).

[yesaya handoyo]

Ok,i get it..I'll try it.Thanks a lot..

[yesaya handoyo]

I want to ask again.How about display the total into the textfield?Suppose i delete a row in the jtable?What should i do to change the sum in the textfield??Thanks a lot..

[Rob Spoor]

If you go through the API, you would find that JTextField has a method called setText.
If you delete a row, just calculate the total from the new contents again. Ideally you would take the total and subtract the value for the row, but once it is deleted you loose that entire row before the event is triggered.

Come to think of it, I think you can do this without TableModelListener if you create your own TableModel:

class MyTableModel extends DefaultTableModel
{
    private BigDecimal total = BigDecimal.ZERO;
 
    // override getColumnClass and isCellEditable as needed
 
    private BigDecimal getTotal(int row)
    {
        BigDecimal price = getValueAt(row, <<column for price>>) ;
        BigDecimal quantity = getValueAt(row, <<column for quantity>>) ;
        if (price == null || quantity == null)
        {
            return BigDecimal.ZERO;
        }
        return price.multiply(quantity);
    }
 
    @Override
    public void setValueAt(Object value, int row, int column)
    {
        if (column == <<column for quantity>> || column == <<column for price>>) 
        {
            BigDecimal oldRowTotal = getTotal(row);
            super.setValueAt(value, row, column);
            BigDecimal newRowTotal = getTotal(row);
            total = total.subtract(oldRowTotal);
            total = total.add(newRowTotal);
        }
        else
        {
            super.setValueAt(value, row, column);
        }
    }
 
    @Override
    public void insertRow(int row, Vector rowData)
    {
        // this method is eventually called by all other addRow and insertRow methods
        super.insertRow(row, rowData);
        BigDecimal rowTotal = getTotal(row);
        total = total.add(rowTotal);
    }
 
    @Override
    public void removeRow(int row)
    {
        BigDecimal rowTotal = getTotal(row);
        super.removeRow(row);
        total = total.subtract(rowTotal);
    }
 
    @Override
    public void setNumRows(int rowCount)
    {
        // also called by setRowCount
        int old = getRowCount();
        BigDecimal remove = BigDecimal.ZERO;
        if (rowCount < old)
        {
            // everything from rowCount to old will be removed
            for (int i = rowCount; i < old; i++)
            {
                BigDecimal rowTotal = getTotal(i);
                remove = remove.subtract(rowTotal);
            }
        }
        // if equal nothing is done, if larger than the values will be 0 or null
        super.setNumRows(rowCount);
        total = total.subtract(remove);
    }
 
    @Override
    public void setDataVector(Vector dataVector, Vector columnIdentifiers)
    {
        super.setDataVector();
        // recalculate total from scratch by iterating through the entire table as in my previous post
    }
}

I may have missed a few methods that can change your table data, but you probably get the idea.

Also note how I only alter total after the call to the parent's method implementation (with super). If for some reason this method throws an exception your total will still be valid.


With this table model your total will always be up-to-date, and you can just retrieve it through a getter method.
[ October 17, 2008: Message edited by: Rob Prime ]

[yesaya handoyo]

Ok,i'll try it out.Suppose using netbeans is no a big difference,isn't it?Thanks..

[Rob Spoor]

I don't know if Netbeans sets a default table model or anything, but you can always override that manually after the Netbeans generated code.

[yesaya handoyo]

Ok,thanks Rob.May God bless you for your help..

[Maya Naga]

...

[Maneesh Godbole]

Ambika,
I am sorry but I had to edit your post. What you had done (posting your question in someone else's post) is called hijacking the thread!
More details here http://faq.javaranch.com/java/UseOneThreadPerQuestion

You can always start a new thread for your question. Also please remember to use code tags
http://faq.javaranch.com/java/UseCodeTags