using a vector instead of array

[JavaBeanie]

I don't think I fully understand this vector this yet. I've got one class that initially uses an array and my assignment is to use a vector. The previous posts in your forums have been very helpful in explaining the vector but i've still got one part that I don't understand.
The original code, that uses the array, looks like this:

public LineItems( int size, SalesInvoice owner )
{
items = new LineItem[ size ];
nItems = size;
for ( int i = 0; i < size; i++ )
{
items[i] = new LineItem( this );
}
this.owner = owner;
}

To change the code to use a vector, I wrote it like this:

public LineItems ( SalesInvoice owner )
{
for ( int i = 0; i < items.size(); i++ )
{
items.add( new LineItem(this) );
}
this.owner = owner;
}

Further into my code I call:

public double getTotal()
{
double total = 0.0;
for ( int i = 0; i < items.size(); i++ )
{
//**getTotal method from LineItemClass
total += items.elementAt( i ).getTotal();
-------------------------^----------^
----------------------error 1----- error 2
}
return total;
}

when I compile I get two errors - error 1 is cannot resolve symbol and error 2 is inconvertiable types (found string/require double). Any advise you could send my way would be greatly appreciated.

[sjalle]

The vector contains LineItem object so get one of them like:

LineItem li=(LineItem)items.elementAt(i);

Then, if a double value is one of the ListItem properties you could get it e.g. like:

double d=li.getTheDoubleValueSomwehereInThere();

[JavaBeanie]

OK-Now this is making much more sense and I thank you. Some of Java's concepts are a little difficult to grasp from a book - your explainations help me a lot - just want to thank you for that.