why get a warning while using the Vector's addElement()?

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iherage@gmail.com - 21 Jun 2005 04:11 GMT

This is part of the code(JDK 1.5 ,windows xp Chinese(simplified))
...

Vector v=new Vector();
v.addElement(new Integer(7));
...

I got a warning.Because I am using a Chinese version,it perhaps means
in English its type is not checked while using the method addElement,so
it is not safe to use it.Why?Is not Integer an Object?And what is the
right way?

Reply to this Message

Ingo R. Homann - 21 Jun 2005 08:07 GMT

Hi,

> This is part of the code(JDK 1.5 ,windows xp Chinese(simplified))
> ...
[quoted text clipped - 7 lines]
> it is not safe to use it.Why?Is not Integer an Object?And what is the
> right way?

The exact warning (in English) would be nice. I guess, you are using
Java5. Try this...

Vector<Integer> v=new Vector<Integer>();
v.addElement(new Integer(7));

...and read something about generics.

Hth,
Ingo

Reply to this Message

iherage@gmail.com - 21 Jun 2005 19:11 GMT

I read the java api doc of jdk 5.0 but it does not say anything about
it.It only says that the parameter is an element.
What about the other collections,LinkedList and ArrayList for
example?Do they have to use in this way?

Reply to this Message

Eric Olander - 21 Jun 2005 22:59 GMT

Generics were added to all the collection classes in 1.5. Check out
http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf

-Eric

>I read the java api doc of jdk 5.0 but it does not say anything about
> it.It only says that the parameter is an element.
> What about the other collections,LinkedList and ArrayList for
> example?Do they have to use in this way?

Reply to this Message

RC - 22 Jun 2005 16:25 GMT

> Hi,
>
[quoted text clipped - 17 lines]
>
> ...and read something about generics.

Great! This is very helpful to me.
But I have different situations.

What happen if I have lines:

Vector v = (Vector)vector.elementAt(i);
v.addElement(new Integer(7));

What should I do?

I wrote:

Vector<Integer> v = (Vector)vector.elementAt(i);

I still got warning

java:778: warning: [unchecked] unchecked conversion
found : java.util.Vector
required: java.util.Vector<java.lang.String>

Where I should put 2nd <Integer>?

Thank Q very much in advance!

Reply to this Message

Ingo R. Homann - 23 Jun 2005 07:48 GMT

Hi RC,

>> The exact warning (in English) would be nice. I guess, you are using
>> Java5. Try this...
[quoted text clipped - 27 lines]
>
> Thank Q very much in advance!

So, "v" is a Vector of Integers, and "vector" is a Vector of "Vector of
Integers"s? Then write this!

Vector<Integer> v;
Vector<Vector<Integer>> vector=...;

v=vector.elementAt(i);
v.addElement(7);

...and read something about "generics"!

Hth,
Ingo

PS: By the way, use ArrayList instead of Vector.

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why get a warning while using the Vector's addElement()?

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