Re: [array / List]Unknown number of objects

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.help

Date:

Thu, 14 Dec 2006 13:22:48 -0800

Message-ID:

<Igjgh.52588$xM4.3994@newsfe07.phx>

Daniel Moyne wrote:

Carl wrote:

Daniel Moyne wrote:

I want to get an array of strings from a method ; as this array has an
unknown number of elements can I use instaed a List to dynamically build
the List and then when finished transform the List into an array in
return ?

Sure, see:

http://java.sun.com/j2se/1.5.0/docs/api/java/util/List.html#toArray(T[])

Carl,
on my way to get a "return array" I tried to compile this found on the net :

import java.util.ArrayList;
import java.util.List;

/** List to array */
public class ToArray {
   public static void main(String[] args) {
     List list = new ArrayList();
     list.add("Blobbo");
     list.add("Cracked");
     list.add("Dumbo");
     // list.add(new Date()); // Don't mix and match!

     // Convert a collection to Object[], which can store objects
     // of any type.
     Object[] ol = list.toArray();
     System.out.println("Array of Object has length " + ol.length);

     // This would throw an ArrayStoreException if the line
     // "list.add(new Date())" above were uncommented.
     String[] sl = (String[]) list.toArray(new String[0]);
     System.out.println("Array of String has length " + sl.length);
   }
}

but I have these error messages that do not make sense to me :
root@azun:/usr/local/Java/genj/report#
$JAVA_HOME/bin/javac -classpath /usr/local/Java/genj/report ToArray.java
Note: ToArray.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
root@azun:/usr/local/Java/genj/report#
$JAVA_HOME/bin/javac -Xlint:unchecked -classpath /usr/local/Java/genj/report
ToArray.java
ToArray.java:8: warning: [unchecked] unchecked call to add(E) as a member of
the raw type java.util.List
     list.add("Blobbo");
             ^
ToArray.java:9: warning: [unchecked] unchecked call to add(E) as a member of
the raw type java.util.List
     list.add("Cracked");
             ^
ToArray.java:10: warning: [unchecked] unchecked call to add(E) as a member
of the raw type java.util.List
     list.add("Dumbo");
             ^
ToArray.java:20: warning: [unchecked] unchecked call to <T>toArray(T[]) as a
member of the raw type java.util.List
     String[] sl = (String[]) list.toArray(new String[0]);
                                          ^
4 warnings

And it is supposed to work according to his author.

If you have explanations help would be appreciated.
Reagrds.

Daniel:

You are having problems because you appear to be using a compiler newer
than when the sample program was written. Take a look at mine below and
I think it will solve all of your questions.

import java.util.*;

public class test {
     public static void main(String[] args) {
         ArrayList<String> list = new ArrayList<String>();
         list.add("Blobbo");
         list.add("Cracked");
         list.add("Dumbo");

         Object[] obj = list.toArray();
         for (int i=0; i<obj.length; i++)
             System.out.println((String)obj[i]);

         String[] array = list.toArray(new String[list.size()]);
         System.out.println("array has length " + array.length);
     }
}

--

Knute Johnson
email s/nospam/knute/