ArrayList problems
I'm new to Java, and I'm having trouble with ArrayLists. I'm working through the exercised in a book called "Objects First with Java". I have an array of type 'Lots' called 'lots'. I want to run go through the array, and add any unsold lots to a new array, then return that array. In another method, I want to loop over the array returned from getUnsold() and print the list. The problem is, the lost is being added to the array as an Object, not a Lot, so I get an error that a 'Lot' was expected but an 'Object' was returned. Am I missing something blindingly obvious here?
public ArrayList getUnsold() {
Iterator it = lots.iterator();
Lot templot;
ArrayList lots;
while(it.hasNext()) {
templot = it.next();
if(templot.getHighestBid() == null) {
unsold.add(templot);
}
}
return unsold;
}
public void showUnsold() {
ArrayList unsold;
unsold = getUnsold();
for(Lot unsoldlot : unsold) {
unsoldlot.toString();
}
}
}
[1052 byte] By [
Echilona] at [2007-11-26 17:20:36]
yep. you need to use [url= http://java.sun.com/j2se/1.5.0/docs/guide/language/generics.html]generics[/url]
> yep. you need to use genericsOr if you're not using 1.5+, you can just cast it.templot = (Lot)it.next();
Or loop through the Lots array directly
public void showUnsold()
{
for (Lot lot : lots)
if (isUnsold(lot))
System.out.println(lot); // toString() called implicitly if it is defined in Lot
}
where function isUnsold(Lot) checks if the lot is infact unsold.
Cheers
> Or loop through the Lots array directlyBut, again, this was new to 1.5.0.
and if you look at the OPs code, he is indeed using enhanced for loops, ergo, java 1.5+
> > Or loop through the Lots array directly
>
> But, again, this was new to 1.5.0.
Yes, so if you're using version < 1.5, use
for (int i = 0; i < lots.length; i++)
if (isUnsold(lots[i]))
// as above
> and if you look at the OPs code, he is indeed using> enhanced for loops, ergo, java 1.5+So he is! Ignore me, please.
Echy, Which version of java are you on 1.5
... as you've heard allready the later versions of Java make like easier for you...
type javac -version at the command prompt to find out... and if that doesn't work try java -version... and if that doesn't work you version of java is too old, [url=http://java.sun.com/javase/downloads/index.jsp]download the 1.6 JDK[/url] from Sun.
Keith.
> Echy, Which version of java are you on 1.5
>
> ... as you've heard allready the later versions of
> Java make like easier for you...
>
> type javac -version at the command prompt to find
> out... and if that doesn't work try java -version...
> and if that doesn't work you version of java is too
> old,
> [url=http://java.sun.com/javase/downloads/index.jsp]do
> wnload the 1.6 JDK[/url] from Sun.
>
> Keith.
see reply #5
The problem's half solved. I've decided to use a for loop instead, but now I'm getting a compile error that the variable 'unsold' might not have been initialised
public ArrayList getUnsold() {
ArrayList<Lot> unsold;
for(Lot templot : lots) {
if(templot.getHighestBid() == null) {
unsold.add(templot);// Error: the unsold variable might not have been initialised
}
}
return unsold;
}
You left unsold unitialized. Also, you should make your return type List<Lot>, not just List or just ArrayList:
public List<Lot> getUnsold() {
List<Lot> unsold = new ArrayList<Lot>();
for(Lot templot : lots) {
if(templot.getHighestBid() == null) {
unsold.add(templot);
}
}
return unsold;
}
Thanks alot, it's much clearer now :)
