Are these Generics Code OK?

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RC - 30 Aug 2006 18:01 GMT

Vector<String []> vector = aFunction();

String[] stringArray;
for (i = 0; i < vector.size(); i++)
stringArray = (String[])vector.get(i);

public Vector<String []> aFunction() {
Vector<String []> v = new Vector<String []>Vector();
String [] sa = new String[10];
int j = 0;
while(j < 10) {
sa[0] = "zero";
sa[1] = "one";
...
sa[9] = "nine";

v.add(sa);
j++;
}
return v;
}

Comppiled by

javac -Xlint MyProgram.java

There is no warning nor error messages.

But I got run-time error

java.lang.ClassCastException: java.lang.String

I think the error is complains about this line:

stringArray = (String[])vector.get(i);

Because that is the only line doing casting.

Any help will be appreciated!

Reply to this Message

Oliver Wong - 30 Aug 2006 18:35 GMT

> Vector<String []> vector = aFunction();
>
[quoted text clipped - 35 lines]
>
> Any help will be appreciated!

This code won't compile. Here's how you can fix it:

<code>
import java.util.Vector;

public class Test {
public static void main(String[] args) {
Vector<String[]> vector = aFunction();

String[] stringArray;
for (int i = 0; i < vector.size(); i++)
stringArray = (String[])vector.get(i);

}

public static Vector<String[]> aFunction() {
Vector<String[]> v = new Vector<String[]>();
String[] sa = new String[10];
int j = 0;
while (j < 10) {
sa[0] = "zero";
sa[1] = "one";
// ...
sa[9] = "nine";

v.add(sa);
j++;
}
return v;
}
}
</code>

this runs without error.

- Oliver

Reply to this Message

Ralf Seitner - 30 Aug 2006 18:44 GMT

Oliver Wong schrieb:

>> Vector<String []> vector = aFunction();
>>
[quoted text clipped - 72 lines]
>
> - Oliver

Hi!
OK. I just wanted to send an answer, but Oliver was quicker than me...
Just one thing, I want to add. You do not have to cast explicitly to
String[], because your vector only contains String[], due to the
declaration Vector<String[]>vector.
bye, Ralf

Reply to this Message

Steve W. Jackson - 30 Aug 2006 18:46 GMT

> Vector<String []> vector = aFunction();
>
> String[] stringArray;
> for (i = 0; i < vector.size(); i++)
> stringArray = (String[])vector.get(i);

Forgetting for the moment that the above code is without context...not
in any class, method, etc...you could make some improvements to the
loop. One thing is that there's no need to cast your "vector.get" to a
String[] since it was explicitly created to contain only such. But then
you can use the improved for loop that comes in 1.5, like this:

for (String[] stringArray : vector) {
// do something here with the current stringArray
}

> public Vector<String []> aFunction() {
> Vector<String []> v = new Vector<String []>Vector();
[quoted text clipped - 29 lines]
>
> Any help will be appreciated!

That last part is a little unclear...how could it compile? What is new
"Vector<String []>Vector();" supposed to mean?

And a ClassCastException should be accompanied by a stack trace that
could show you the exact line where it originates. But since the above
is fragmented and cannot be compiled as presented, it's not clear what
your problem might be.

Signature

Steve W. Jackson
Montgomery, Alabama

Reply to this Message

RC - 30 Aug 2006 19:56 GMT

> That last part is a little unclear...how could it compile? What is new
> "Vector<String []>Vector();" supposed to mean?

Sorry, that is typo error. It should be

Vector<String []> v = new Vector<String []>();

Reply to this Message

Chris Smith - 31 Aug 2006 05:14 GMT

> > That last part is a little unclear...how could it compile? What is new
> > "Vector<String []>Vector();" supposed to mean?
>
> Sorry, that is typo error. It should be
>
> Vector<String []> v = new Vector<String []>();

Just out of curiosity, did you actually retype all of your code into
your news client? If so, wow. That is not only bad for us, since
you're bound to produce typos, but it must also be a real pain for you
as well! Copy and paste really is much easier.

Signature

Chris Smith

Reply to this Message

Are these Generics Code OK?

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