implement AbstractTableModel for a Java collection

问题:

I'm trying to implement an AbstractTableModel for a collection named "clients" but I keep receiving the error "required variable found value" for the "add" method. Here is my code:

I'm sorry for the confusion created. The add method is meant to add a new client in the table (by that I mean a new row). I don't want to add a new client to the collection.

class ModelTabel extends AbstractTableModel{

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

    public int getColumnCount() {
        return 4;
    }

    public Object getValueAt(int row, int column) {
        Client c = clients.get(row-1);
        switch(column){
            case 0: return c.getName();
            case 1: return c.getSurname();
            case 2: return c.getID();
            case 3: return c.getPhone();
            default:return "ERROR";
        }
    }

    public void add(Client c) {
        clients.get(clients.size()++) = a;
        fireTableDataChanged();
        }
    }

回答1:

I believe this is the same problem as this question... your variable assignment is reversed.

It should be (although this code is still incorrect - see below):

a = clients.get(clients.size()++);

EDIT: this was already answered by Prabhakaran, but apparently people felt the need to downvote my answer.. I think I did address the original question, but I appreciate that my code sample was still incorrect, so I will try to provide a more complete answer:

First of all, as to the "required variable not found" error, if you google it you will see that other SO question as the first hit. clients.get(clients.size()++) is not a variable, so you can't assign things to it. I am not sure where a is declared in your code, but assume that it is a variable and thus my suggestion of reversing the assignment.

Next, for the clients.get(clients.size()++) line, as others have mentioned or alluded to - VAR++ is equivalent to VAR = VAR + 1, so again is an assignment operation going on. In this case, clients.size() is not a variable, so you can not increment it. If you wanted the clients.size() + 1 index, you could have written: a = clients.get(clients.size() + 1)... but that will throw an ArrayIndexOutOfBoundsException, because you're trying to access an element of clients beyond its current size!

That is why Prabhakaran rewrote your method as they did, changing that line to a clients.add(c) call - as it seemed to fit the original intent of the method.

回答2:

You can't ++ the return value from a method, because the argument of ++ has to be something that is valid on the left hand side of an assignment. If you want to add something to the end of a Collection then the correct way to do that is to use the add method.

clients.add(a);

Also, you should fire a more specific modification event than simply "table changed". Calling fireTableDataChanged essentially tells listeners "the data in this model has changed beyond recognition, throw away your current visual representation and build a completely new one instead". It would be much more efficient and provide a better user experience if instead you used

fireTableRowsInserted(clients.size() - 1, clients.size() - 1);

which specifically says "one new row has been added to the end of this model, but the rest of the data is unchanged".

回答3:

do like this

change

clients.get(clients.size()++) = a;

to

clients.add(c); 

Now your method looks like

public void add(Client c) {
    clients.add(c); 
    fireTableDataChanged();
    }
}

Not sure how you getting clients.size(); believing clients Collection present in ModelTabel class.

回答4:

Just keep it simple. You have an arraylist of clients right?

class ModelTabel extends AbstractTableModel{

    ArrayList<Client> clients = new ArrayList<Client>();

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

    public int getColumnCount() {
        return 4;
    }

    public Object getValueAt(int row, int column) {
        Client c = clients.get(row);
        switch(column){
            case 0: return c.getName();
            case 1: return c.getSurname();
            case 2: return c.getID();
            case 3: return c.getPhone();
            default:return "ERROR";
        }
    }

    public void add(Client c) {
        clients.add(c);
        fireTableDataChanged();
        }
    }

回答5:

Please show the full error message, not a paraphrasing of the error. Please show the line of text that causes the error.

Having said that, where is your clients variable? Where is it declared? Initialized? I think that your model needs this to work and to make sense.

回答6:

It would help if you show how your collection (I'm assuming it's a List? is being declared.

That being said, your add method doesn't make sense: I think you mean:

{
  clients.add( c );
  fireTableDataChanged()
}