Why does List.toArray() return an array of Object? [duplicate]

Question

Possible Duplicate:
why does List<String>.toArray() return Object[] and not String[]? how to work around this?

See this code example :

    List<String> list = new ArrayList<String>();
    list.add("hello");
    list.add("world");
    Object [] array = list.toArray();

Why does the method toArray() return an array of Object ? Other List methods such as get() , remove() are able to return the type of objects in the list.

@SuperChafouin please do some research before posting a question. — Luiggi Mendoza
– Luiggi Mendoza, Commented Jun 13, 2012 at 4:03
Ok, this answers to my question : http://stackoverflow.com/a/7909755/1075341 I mark my question as duplicate. — Arnaud
– Arnaud, Commented Jun 13, 2012 at 4:20
For those interested in that question, i found the best way to understand is to try to program your own implementation of toArray using generics or to look at ArrayList code, for example. — Arnaud
– Arnaud, Commented Jun 13, 2012 at 4:34

Priyanshu Jha · Accepted Answer · 2012-06-13 03:59:24Z

1

you can use toArray(String[] a) which will return array of string type or basically array of specified type. the toArray method returns object as it acts as bridge between Collection based and List based API.

answered Jun 13, 2012 at 3:59

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Priyanshu Jha

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Frank Sposaro · Accepted Answer · 2012-06-13 03:57:23Z

0

I believe is returns Object in order to be generic Most likely it has to deal with memory allocation issues. The system doesn't have to know your exact type inorder to allocate an array of Objects. You don't run into this with get and remove since it's only returning one item.

But I will upvote your question in hope someone can confirm my answer or correct me.

answered Jun 13, 2012 at 3:57

Frank Sposaro

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Luiggi Mendoza · Accepted Answer · 2012-06-13 04:00:42Z

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The Java List#toArray explains it.

edited Jun 13, 2012 at 4:00

Luiggi Mendoza

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answered Jun 13, 2012 at 3:57

Raghuram

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2 Comments

Wingman4l7 Over a year ago

The answer was accidentally formatted as code -- fixed!

Luiggi Mendoza Over a year ago

From now on, please refer to a valid documentation. The link was pointing to Java 1.4, there is new documentation in Java 6 and Java 7.

Op De Cirkel · Accepted Answer · 2012-06-13 04:05:46Z

0

toArray() has to construct new array object and fill it up. But because of runtime generic type erasure toArray() does not know what is the actual type of the elements. because of that creates array of Object (Object[]). Use <T> T[] toArray(T[] a) if you want typed array.

answered Jun 13, 2012 at 4:05

Op De Cirkel

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