Java Convert Object[] Array to Vector

Question

What's the best way to convert an Object array to a Vector?

JDE < 1.5

public Vector getListElements()
{
  Vector myVector = this.elements;
  return myVector;
}

this.elements is an Object[]

Thanks, rAyt

I should clarify my question

My target platform is a blackberry.

Collections aren't supported. Array.asList() isn't, either :/

Full Class

package CustomElements;

import net.rim.device.api.ui.component .*;
import net.rim.device.api.collection.util.*; 
import net.rim.device.api.util.*;
import java.util.*;

public class ContactsList extends SortedReadableList implements KeywordProvider
{
    // Constructor
    public ContactsList(Vector contacts)
    {
        super(new ContactsListComparatorByFirstName());    
        loadFrom(contacts.elements());      
    }
    // Add Element to ContactsSortedReadableList
    void addElement(Object element)
    {
        doAdd(element); 
    }   

    public Vector getListElements()
    {
        return new Vector(Collection


        Vector test = this.getElements();
    }
    // getKeywords
    public String[] getKeywords(Object element) 
    {
        return StringUtilities.stringToWords(((Contact)element).get_contactFirstName());
        // return StringUtilities.stringToWords(element.toString());
    }  
    //  Comparator sorting Contact objects by name
    final static class ContactsListComparatorByFirstName implements Comparator
    {                           
        public int compare(Object o1, Object o2)
        {
            // Sticky Entries Implementation
            if(((ContactsListObject)o2).getSticky())
            {
                return 1;
            } else
                if (((ContactsListObject)o1).getSticky())
                {
                    return -1;
                } else
                {
                    if(((ContactsListObject)o1).get_contactFirstName().compareTo(((ContactsListObject)o2).get_contactFirstName()) <0)
                    {
                        return -1;
                    }
                    if(((ContactsListObject)o1).get_contactFirstName().compareTo(((ContactsListObject)o2).get_contactFirstName()) >0)
                    {
                        return 1;
                    }
                    else
                    {
                        return 0;
                    }
                }
        }        
    }    
}

Tom Hawtin - tackline · Accepted Answer · 2009-07-12 19:12:19Z

38

return new Vector(Arrays.asList(elements));

Now, it may look as if you are copying the data twice, but you aren't. You do get one small temporary object (a List from asList), but this provides a view of the array. Instead of copying it, read and write operations go through to the original array.

It is possible to extends Vector and poke its protected fields. This would give a relatively simple way of having the Vector become a view of the array, as Arrays.asList does. Alternatively, just copying data into the fields. For Java ME, this is about as good as it gets without writing the obvious loop. Untested code:

return new Vector(0) {{
    this.elementData = (Object[])elements.clone();
    this.elementCount = this.elementData.length;
}};

Of course, you are probably better off with a List than a Vector. 1.4 has completed its End of Service Life period. Even 1.5 has completed most of its EOSL period.

edited Jul 12, 2009 at 19:12

answered Jul 12, 2009 at 18:46

Tom Hawtin - tackline

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2 Comments

Henrik P. Hessel Over a year ago

Wow, second solution looks, just so elegant!

Tom Hawtin - tackline Over a year ago

I think "inventive" needs quotes. :)

jqno · Accepted Answer · 2009-07-12 18:58:09Z

2

In J2ME, you're stuck iterating over the array and add the elements one by one.

Vector v = new Vector();
for (int i = 0; i < this.elements.length; i++) {
    v.add(this.elements[i]);
}

edited Jul 12, 2009 at 18:58

answered Jul 12, 2009 at 18:47

jqno

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1 Comment

Henrik P. Hessel Over a year ago

Should I understand why Research in Motion provide something like SortedReadableList which has an LoadFrom Method, but no LoadTO Method?! :)

Peter Lawrey · Accepted Answer · 2009-07-12 19:13:38Z

1

A simplified comparator which does basically the same thing.

final static class ContactsListComparatorByFirstName implements Comparator {
    public int compare(Object o1, Object o2) {
            // Sticky Entries Implementation
        ContactsListObject clo2 = (ContactsListObject) o2;
        ContactsListObject clo1 = (ContactsListObject) o1;
        if (clo2.getSticky()) return 1;
        if (clo1.getSticky()) return -1;
        return clo1.get_contactFirstName().compareTo(clo2.get_contactFirstName());
    }
}

Using generics and ?: it would be just

static final class ContactsListComparatorByFirstName implements Comparator<ContactsListObject> {
    public int compare(ContactsListObject clo1, ContactsListObject clo2) {
        return clo2.getSticky() ? 1 : // Sticky Entries Implementation
            clo1.getSticky() ? -1 :
            clo1.get_contactFirstName().compareTo(clo2.get_contactFirstName());
    }
}

But to answer your question... (oh I see Tom has what I would put already)

answered Jul 12, 2009 at 19:13

Peter Lawrey

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1 Comment

Henrik P. Hessel Over a year ago

Generics aren't supported in my java version, either! But thanks for the hint +1

dfa · Accepted Answer · 2009-07-12 20:09:44Z

1

imho your only viable option is:

public Vector getListElements()
    Vector vector = new Vector(this.elements.length);

    for (int i = 0; i < this.elements.length; i++) {
        vector.add(this.elements[i]);
    } 

    return vector;
}

edited Jul 12, 2009 at 20:09

answered Jul 12, 2009 at 18:57

dfa

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2 Comments

Henrik P. Hessel Over a year ago

Yeah, seems that way. going to suck copying 1000+ objects in the objects array.

Carl Manaster Over a year ago

If you're concerned about it, you could toss in an initialCapacity of elements.length to the Vector constructor.

bluish · Accepted Answer · 2013-06-06 13:55:11Z

1

Copy the array elements to the Vector, or
Use Arrays.asList(...) to return a List, which isn't exactly a Vector, but you should be coding the List interface anyway.

edited Jun 6, 2013 at 13:55

bluish

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answered Jul 12, 2009 at 18:45

camickr

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3 Comments

Henrik P. Hessel Over a year ago

So, no way around a for loop?

Peter Lawrey Over a year ago

I suggest option 2 except it is worth noting that this does not take a copy of the array, it only wraps it. I wouldn't suggest option 1 i.e. don't use a vector unless you really need to.

mechanical_meat Over a year ago

@rAyt: Even if there was a built-in function to do so, it would still use a for-loop behind the scenes. There is no magic :)

Klaus Engelhardt · Accepted Answer · 2018-04-17 14:26:31Z

1

A reasonably concise way to do it is something like:

Object[] xx = { 1, "cat", new Point(100,200) };
Vector vv = new Vector(Arrays.asList(xx));
System.out.println("vv=="+vv.toString());

But y'all knew that already, I guess.

answered Apr 17, 2018 at 14:26

Klaus Engelhardt

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