How to return a list of generic type

I can create a method that takes a Class as parameter and return the same type:
public <T> T getSomthing(Class<T> c) throws Exception {
return c.newInstance();
}My question is, can I modify this method to return a List of the same type as input class c? If so, how?

Hi,
import java.util.ArrayList;
import java.util.List;
public class ReturnList {
    @SuppressWarnings("unchecked")
    public <T> List<T> getList() {
     return new ArrayList();
}Piet

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Hi,
I need to create a typed array T[] from an object array Object[]. This is due to legacy code integration with older collections.
The method signature is simple:public static <T> T[] toTypedArray(Object[] objects)I tried using multiple implementations and go over them in the debugger. None of them create a typed collection as far as I can tell. The type is always Object[].
A simple implementation is just to cast the array and return, however this is not so safe.
What is interesting is that if I create ArrayList<String>, the debugger shows the type of the array in the list as String[].
If I create ArrayList<T>, the class contains Object[] and not T[].
I also triedT[] array = (T[]) Array.newInstance(T[].class.getComponentType(), objects.length);And a few other combinations. All work at runtime, create multiple compilation warnings, and none actually creates T[] array at runtime.
Maybe I am missing something, but Array.newInstace(...) is supposed to create a typed array, and I cannot see any clean way to pass Class<T> into it.T[].class.getComponentType()Returns something based on object and not on T, and T.class is not possible.
So is there anything really wrong here, or should I simply cast the array and live with the warnings?
Any help appreciated!

Ok. May be you could keep information about generic type in the your class:
public class Util {
    public static <T> T[] toTypedArray(Class<T> cls, Object[] objects){
        int size = objects.length;
        T[] t = (T[]) java.lang.reflect.Array.newInstance(cls, size);
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public class Sample<T> {
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}

How to return a list of class from a package

Hi,
I'm trying to create a RPG game with 50 characters. There will be a superclass, and each character is a subclass that extends from the superclass. Each will have unique abilities that will be functions. These classes will be thrown into a package.
I would like to know the code for returning the list of classes in that package. That way, I can present them as a list for the player to choose just a handful of characters to start out with.
Thanks in advance

Hi u can use the this class
flash.utils.describeType;
Regards
Sumit Agrawal

How to return Values from Oracle Object Type to Java Class Object

Hello,
i have created an Oracle Object Types in the Database. Then i created Java classes with "jpub" of these types. Here is an example of the type.
CREATE OR REPLACE TYPE person_type AS OBJECT
ID NUMBER,
vorname VARCHAR2(30),
nachname VARCHAR2(30),
geburtstag DATE,
CONSTRUCTOR FUNCTION person_type RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION person_type(p_id NUMBER) RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION person_type(p_vorname VARCHAR2,
p_nachname VARCHAR2,
p_geburtstag DATE) RETURN SELF AS RESULT,
MEMBER FUNCTION object_exists(p_id NUMBER) RETURN BOOLEAN,
MEMBER PROCEDURE load_object(p_id NUMBER),
MEMBER PROCEDURE save_object,
MEMBER PROCEDURE insert_object,
MEMBER PROCEDURE update_object,
MEMBER PROCEDURE delete_object
MEMBER PROCEDURE load_object(p_id NUMBER) IS
BEGIN
SELECT p.id, p.vorname, p.nachname, p.geburtstag
INTO SELF.ID, SELF.vorname, self.nachname, SELF.geburtstag
FROM person p
WHERE p.id = p_id;
END;
My problem is, that if i use the member function "load_object" from my java app it doesnt return the selected values to the java class and i dont know why. I use the java class like this:
PersonObjectType p = new PersonObjectType();
p.load_object(4);
There is a reocrd in the database with id = 4 and the function will execute successful. But if i try to use "p.getVorname()" i always get "NULL". Can someone tell me how to do that?
Thanks a lot.
Edited by: NTbc on 13.07.2010 15:36
Edited by: NTbc on 13.07.2010 15:36

CallableStatement =
"DECLARE
a person_type;
BEGIN
a.load_object(4);
? := a;
END;"
And register as an out parameter.
Edited by: michael76 on 14.07.2010 05:01

How to return a list?

Hi m assignment is to create a linked list implementation..
so far i have this..
public class Set<Value> {
Value Element;
Set<Value> next;
Set(Value data)
            Element=data;
            next=null;
        Set(Value data, Set n)
            Element = data;
            next    = n;
public interface MySet<Value> {
boolean isIn(Value v);
void add(Value v);
void remove(Value v);
MySet union(MySet s);
MySet intersect(MySet s);
MySet difference(MySet s);
int size();
void printSet();
public class MyLLSet<Value> implements MySet<Value>{
    private Set<Value> head;
public MyLLSet(){
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public boolean isIn(Value v){
    Set<Value> p;
    p=head;
    boolean flag=false;
     while(p.next!=null){
        p=p.next;
        if(p.Element==v){
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return flag;
public void add(Value v){
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    Set<Value> q;
    p=head;
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    while(p.next!=null){
        p=p.next;
        q=q.next;
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public void remove(Value v){
Set<Value> p;
Set<Value> q;
p=head;
q=head.next;
while(p.next!=null){
     p=p.next;
     q=q.next;
     if(p.Element==v){
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         break;
public MySet union(MyLLSet s){
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    Set<Value> q;
    p=s.head;
    q=this.head;
    while(p.next!=null){
        p=p.next;
    p=q.next;
    s.head.next=null;
RETURN ???
}However in my union method i cant figure out what to return.. i am sure that the method creates a union of two lists.. but how do i return the final unionized list.... ( i am new to programming so sorry if i dont make sense)
Edited by: haramino1 on Mar 22, 2009 1:31 PM

Have some patience! You can't expect an answer in 10 minutes.
Your original post looked like you wanted to make an implementation of a linked list, using a set as the underlying code (which doesn't make a lot of sense). However, your real assignment, as you stated later, is to make an implementation of a set, with a linked list as the underlying code.
In your original post, your Set<Value> doesn't make sense to be your Set class. It does make sense to have that code as your linked list's "node" class. So, rename it from Set<Value> to Node<Value>. Everywhere in that class that says "Set" should say "Node". It will only confuse you more if you call it "Set" when it is not a "Set" (it surely confused me!). Also, "Element" should be lowercase "element" (to follow standard naming conventions).
You want to make a linked list class that implements everything in the MySet<Value> interface. So, your MyLLSet<Value> should have all of those methods. Your MyLLSet should have one variable (which you have, but you call it Set<Value>, it should be Node<Value>).
private Node<Value> head;Your MyLLSet constructor probably shouldn't set head to a new Node with a null value (otherwise, your Set will always include a null member). The MyLLSet constructor probably doesn't need to do anything, so you can just remove that whole constructor and let the compiler generate its standard no-argument constructor.
When comparing values for equality in isIn, you probably want to use .equals, not ==:
if (p.element == v) // WRONGshould be:
if (p.element.equals(v)) // CORRECTOtherwise, you are only comparing reference values, not the data they point to. So, for instance, if Value was a String, you wouldn't be able to write code that asked the user for a String value to test if the String was in the Set--I don't think you'd ever be able to get "true" for the answer.
In isIn, your test should not be p.next != null --it should be "p != null". Otherwise, if p is null, you will get a NullPointerException trying to get "next". You want:
while (p != null) {
   // Test p.element for equality to v.
   //        If equal, you can break out of the 'for' loop.
   // Set p to p.next.
}Similarly in other methods, you need to check p != null . Your 'add' method is wrong--you didn't check duplicates, for one thing. Your loop isn't right, either.

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          oscar alarcon wrote:
          >
          > I have a servlet that do a call service to another machine( the service
          > can be so different), and I would like to know if there is possible to
          > return the "servletresult" in the "httpservletresult" or somethiing
          > similar,because
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          > manipule these parameters in the client. So, i want don´t use
          > "getParameterValues" of "servletresult".
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Maybe it is there and I'm just not seeing it. Do you know of another way, using reflection, to get from a string "my.package.Foo" to a Class<Foo> object?
Thanks again for your help,
Gary

How to return a list of generic type

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