How to interpret and use generic vector?

Question

Can any body explain this generic vector Vector<? super Object> list = ... and where to use it?

Most consider it deprecated. It's basically a synchronized List... http://stackoverflow.com/questions/1386275/why-is-java-vector-class-considered-obsolete-or-deprecated — Peter Svensson, Sep 11 '12 at 12:01
I wouldn't use Vector, I would use List and ArrayList. I wouldn't use `? super Object` which is the same as `Object` as its plain confusing. — Peter Lawrey, Sep 11 '12 at 12:05

score 4 · Answer 1 · answered Sep 11 '12 at 12:05

It is the same as

Vector<Object> list

Usually "? super Type" means that you can add supertypes of type Type

Object is the highest level in Java so there are no supertypes so the ? super is not needed

If it was

Vector<? extends Object> list

then it would mean that you can add any object that is a subclass of Object. This is every object in Java so it would be the same as

Vector<Object> list

Also consider List rather than Vector and if you want it thread safe then wrap it in Collections.synchronizedList(...)

`Vector extends Object>` is not the same as `Vector – assylias Sep 11 '12 at 12:12 — assylias, Sep 11 '12 at 12:12

basiljames · Accepted Answer · 2012-09-11T12:28:51.383

4

Here you are defining the lower bound of your unknown object ?. So the Vector<? super Object can contain only Object and any super class of Object. But since Object does'nt have a super class it has no sense. It behaves same as Vector<Object>.

Refer this sample.

The counterpart for this is upper bound Vector<? extends Object> where you can add any object that extends Object.

You should be able to avoid using Object as the generic type is most cases.

edited Sep 11 '12 at 12:28

answered Sep 11 '12 at 12:10

basiljames

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Does it means if i have my own object it will be useful to use it?if yes how can it be useful? let say like this example: `List super MyObject> list = ...` – itro Sep 11 '12 at 12:25
Yes. In that case you can add `MyObject` and any parent classes of `MyObject`. – basiljames Sep 11 '12 at 12:32

score 3 · Answer 3 · answered Sep 11 '12 at 12:05

3

<? super Object> is absurd since there is no super type of Object, but it is allowed, and it consists of just Object types. http://www.angelikalanger.com/GenericsFAQ/FAQSections/TypeArguments.html

answered Sep 11 '12 at 12:05

Erhan Bagdemir

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score 1 · Answer 4 · answered Sep 11 '12 at 12:05

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Such a list can only contain elements of type Object as Object doesn't have any super types similar to using extends of with an immutable class like String where such a collection can contain only Strings.

answered Sep 11 '12 at 12:05

Vikdor

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How to interpret and use generic vector?

4 Answers4