I took this one step further
ArrayList<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(1);
list.add(2);
list.add(3);
HashSet<Integer> set = new HashSet<Integer>();
set.addAll(list);
System.out.println(list.size());
System.out.println(set.size());
output:
4
3
So java will remove all duplicates that it finds.
On Tue, Apr 7, 2009 at 7:59 AM, Brandon Goodin <brandon.goo...@gmail.com>wrote:
> Wrote this too and it worked:
>
> 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(list);
>
> System.out.println(set.size());
>
>
> Brandon
>
>
> On Tue, Apr 7, 2009 at 8:57 AM, Brandon Goodin
> <brandon.goo...@gmail.com>wrote:
>
>> 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 <
>> iloetz...@asci-systemhaus.de> 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 <ferknj...@gmail.com
>>> > <mailto:ferknj...@gmail.com>> 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 <larry.mead...@gmail.com
>>> > <mailto:larry.mead...@gmail.com>>
>>> >
>>> > return new LinkedHashSet(queryForList(...));
>>> >
>>> > Larry
>>> >
>>> >
>>> > On Sun, Apr 5, 2009 at 10:53 PM, fer knjige <
>>> ferknj...@gmail.com
>>> > <mailto:ferknj...@gmail.com>> 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!
>>>
>>>
>>
>
