I took a few seconds and wrote this....
ArrayList list = new ArrayList();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
list.add("e");
list.add("f");
HashSet set = new HashSet();
set.addAll(list);
System.out.println(set.size());
Bon Appetit,
Brandon
On Tue, Apr 7, 2009 at 3:57 AM, Ingmar Lötzsch <[email protected]
> wrote:
> > This is a fundamental java issue. You will never be able to cast a list
> > to a set because a list allows duplicates whereas a set dose not.
>
> The duplicates are not the reason. ArrayList is not a subtype of Set.
> And how does the query
>
> select * from Products
>
> produce duplicates?
>
> Lists accept duplicates. Copy the following code in a class and run the
> main method:
>
> package test;
>
> import java.util.ArrayList;
> import java.util.HashSet;
> import java.util.Set;
>
> public class ListSetConversionTest
> {
> public static void main(String[] args)
> {
> ArrayList<Integer> intList = new ArrayList<Integer>();
> Integer zero = Integer.valueOf(0);
> intList.add(zero);
> intList.add(zero);
> Set<Integer> intSet = new HashSet<Integer>(intList);
> System.out.println(intSet);
> Set<Integer> intSet2 = new HashSet<Integer>();
> intSet2.addAll(intList);
> System.out.println(intSet2);
>
> String[][] productDataList =
> {
> {"1", "Product 1"},
> {"1", "Product 1"},
> {"2", "Product 2"},
> {"2", "Product 2"}
> };
>
> ArrayList<Product> productList = new ArrayList<Product>();
> for (String[] productData : productDataList)
> {
> Product product = new Product();
> Integer id = Integer.valueOf(productData[0]);
> product.setId(id);
> product.setName(productData[1]);
> productList.add(product);
> }
> Set<Product> productSet = new HashSet<Product>(productList);
> System.out.println(productSet);
> }
>
> protected static class Product
> {
> Integer id;
>
> String name;
>
> public Integer getId()
> {
> return this.id;
> }
>
> public void setId(Integer id)
> {
> this.id = id;
> }
>
> public String getName()
> {
> return this.name;
> }
>
> public void setName(String name)
> {
> this.name = name;
> }
>
> @Override
> public String toString()
> {
> return this.id + " " + this.name;
> }
> }
> }
>
> You see, that there are (intList, productList) duplicates in both lists.
> Both intSets don't contain duplicates, but the productSet does.
>
> If you want to make the products "unique" in the set, you have to
> override the equals() and perhaps the hashcode() methods (I' am not an
> expert for this.)
>
> There
> > is no way for java to know which of the duplicate elements it should
> > use. If you guarantee that you have unique result from your DB(i.e. use
> > the unique keyword), then you can programatically create a set from a
> list.
> >
> > off the top of my head....
> >
> > List<Product> products =
> (List<Product>)queryForList("Products.selectAll");
> > HashSet<Product> productsSet = new HashSet<Product>(products.size());
> > for(Product p:products) {
> > productsSet.add(p);
> > }
>
> Of course the best way is to avoid duplicates in the query and use the
> code from Larry Meadors:
>
> return new LinkedHashSet(queryForList(...));
>
> LinkedHashSet (instead of HashSet) preserves the order.
>
> > On Mon, Apr 6, 2009 at 10:53 PM, fer knjige <[email protected]
> > <mailto:[email protected]>> wrote:
> >
> > Unfortunately this doesn't work. It returns following error:
> >
> > Exception in thread "main" java.lang.ClassCastException:
> > java.util.ArrayList.
> >
> > Solution?
> >
> > 2009/4/6 Larry Meadors <[email protected]
> > <mailto:[email protected]>>
> >
> > return new LinkedHashSet(queryForList(...));
> >
> > Larry
> >
> >
> > On Sun, Apr 5, 2009 at 10:53 PM, fer knjige <[email protected]
> > <mailto:[email protected]>> wrote:
> > > Hi,
> > >
> > > I have a simple query:
> > >
> > > select * from Products.
> > >
> > > I want to have results in Set not in List. How can I do it
> since
> > > method 'queryForList' returns only List?
> > >
> > > Thanks in advance!
>
>
