Re: Can I use Set instead of List?
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)
{
ArrayListInteger intList = new ArrayListInteger();
Integer zero = Integer.valueOf(0);
intList.add(zero);
intList.add(zero);
SetInteger intSet = new HashSetInteger(intList);
System.out.println(intSet);
SetInteger intSet2 = new HashSetInteger();
intSet2.addAll(intList);
System.out.println(intSet2);
String[][] productDataList =
{
{1, Product 1},
{1, Product 1},
{2, Product 2},
{2, Product 2}
};
ArrayListProduct productList = new ArrayListProduct();
for (String[] productData : productDataList)
{
Product product = new Product();
Integer id = Integer.valueOf(productData[0]);
product.setId(id);
product.setName(productData[1]);
productList.add(product);
}
SetProduct productSet = new HashSetProduct(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
ListProduct products = (ListProduct)queryForList(Products.selectAll);
HashSetProduct productsSet = new HashSetProduct(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!
Re: Can I use Set instead of List?
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)
{
ArrayListInteger intList = new ArrayListInteger();
Integer zero = Integer.valueOf(0);
intList.add(zero);
intList.add(zero);
SetInteger intSet = new HashSetInteger(intList);
System.out.println(intSet);
SetInteger intSet2 = new HashSetInteger();
intSet2.addAll(intList);
System.out.println(intSet2);
String[][] productDataList =
{
{1, Product 1},
{1, Product 1},
{2, Product 2},
{2, Product 2}
};
ArrayListProduct productList = new ArrayListProduct();
for (String[] productData : productDataList)
{
Product product = new Product();
Integer id = Integer.valueOf(productData[0]);
product.setId(id);
product.setName(productData[1]);
productList.add(product);
}
SetProduct productSet = new HashSetProduct(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
ListProduct products =
(ListProduct)queryForList(Products.selectAll);
HashSetProduct productsSet = new HashSetProduct(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!
Re: Can I use Set instead of List?
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.comwrote:
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)
{
ArrayListInteger intList = new ArrayListInteger();
Integer zero = Integer.valueOf(0);
intList.add(zero);
intList.add(zero);
SetInteger intSet = new HashSetInteger(intList);
System.out.println(intSet);
SetInteger intSet2 = new HashSetInteger();
intSet2.addAll(intList);
System.out.println(intSet2);
String[][] productDataList =
{
{1, Product 1},
{1, Product 1},
{2, Product 2},
{2, Product 2}
};
ArrayListProduct productList = new ArrayListProduct();
for (String[] productData : productDataList)
{
Product product = new Product();
Integer id = Integer.valueOf(productData[0]);
product.setId(id);
product.setName(productData[1]);
productList.add(product);
}
SetProduct productSet = new
HashSetProduct(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
ListProduct products =
(ListProduct)queryForList(Products.selectAll);
HashSetProduct productsSet = new HashSetProduct(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
Re: Can I use Set instead of List?
I took this one step further
ArrayListInteger list = new ArrayListInteger();
list.add(1);
list.add(1);
list.add(2);
list.add(3);
HashSetInteger set = new HashSetInteger();
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.comwrote:
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.comwrote:
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)
{
ArrayListInteger intList = new ArrayListInteger();
Integer zero = Integer.valueOf(0);
intList.add(zero);
intList.add(zero);
SetInteger intSet = new HashSetInteger(intList);
System.out.println(intSet);
SetInteger intSet2 = new HashSetInteger();
intSet2.addAll(intList);
System.out.println(intSet2);
String[][] productDataList =
{
{1, Product 1},
{1, Product 1},
{2, Product 2},
{2, Product 2}
};
ArrayListProduct productList = new ArrayListProduct();
for (String[] productData : productDataList)
{
Product product = new Product();
Integer id = Integer.valueOf(productData[0]);
product.setId(id);
product.setName(productData[1]);
productList.add(product);
}
SetProduct productSet = new
HashSetProduct(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
ListProduct products =
(ListProduct)queryForList(Products.selectAll);
HashSetProduct productsSet = new HashSetProduct(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
Re: Can I use Set instead of List?
No, but you can create a set from the list though. If you need to remove duplicates, why don't you change the query to be unique? -Richard Sent from my iPhone On Apr 5, 2009, at 9:53 PM, fer knjige 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!
Re: Can I use Set instead of List?
return new LinkedHashSet(queryForList(...)); Larry On Sun, Apr 5, 2009 at 10:53 PM, fer knjige 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!
Re: Can I use Set instead of List?
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 return new LinkedHashSet(queryForList(...)); Larry On Sun, Apr 5, 2009 at 10:53 PM, fer knjige 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!
Re: Can I use Set instead of List?
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. 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
ListProduct products = (ListProduct)queryForList(Products.selectAll);
HashSetProduct productsSet = new HashSetProduct(products.size());
for(Product p:products) {
productsSet.add(p);
}
On Mon, Apr 6, 2009 at 10:53 PM, fer knjige 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
return new LinkedHashSet(queryForList(...));
Larry
On Sun, Apr 5, 2009 at 10:53 PM, fer knjige 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!
Can I use Set instead of List?
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!
