Re: [array / List]Unknown number of objects

Daniel Moyne <>
Fri, 15 Dec 2006 12:16:50 +0100
Knute Johnson wrote:

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:[])

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(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 :
$JAVA_HOME/bin/javac -classpath /usr/local/Java/genj/report
Note: uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
$JAVA_HOME/bin/javac -Xlint:unchecked -classpath
/usr/local/Java/genj/report warning: [unchecked] unchecked call to add(E) as a member
of the raw type java.util.List
             ^ warning: [unchecked] unchecked call to add(E) as a member
of the raw type java.util.List
             ^ warning: [unchecked] unchecked call to add(E) as a
member of the raw type java.util.List
             ^ 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.


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>();

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

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

thanks for your help so basically it was a proper list of import ; error
messages provided by javac should be clearer !.

As the main objective of my question was to get a way to feed an array of
unknown number of elements and therefore use an ArrayList, here is my piece
of work where I handle data though an ArrayList and return an array ; it
works neatly.

public String[] getAllClassName(Indi indi) {
    /* check for existing classes */
    /* not very efficient as we do not have a class names list */
    Locale frLocale = new Locale("fr","FR","fr_FR.UTF-8");
    Collator myCollator = Collator.getInstance(frLocale);
    ArrayList<String> classnamelist = new ArrayList<String>();
    String classname;
    Boolean errorflag=false;
    Property classnameproperties[];
    Indi indi_;
    Gedcom gedcom=indi.getGedcom();
    Collection indis=gedcom.getEntities(Gedcom.INDI);
    for (Iterator it=indis.iterator(); it.hasNext();) {
        /* we get all _CLAS properties from all INDI's */
        /* we get all _CLAS property values from all INDI's */
        /* if no _CLAS tags we do nothing */
        if (classnameproperties.length != 0) {
            /* there are _CLAS tags */
            /* we want to collect the _CLAS tag value */
            for (int i=0; i<classnameproperties.length; i++) {
                if (!classnamelist.contains(classname)) {
                    /* classname not included yet in classnamelist */
                    /* we add it */
    /* we sort the arraylist alphabetically */
    /* we return an array */
    return classnamelist.toArray(new String[classnamelist.size()]);

Thanks again !

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