ClassCastException from Vector to Array

[vhqd]

hello, my trouble is exampled in the code. Please take a look and give
me some threads. thanks.

TestArray.java
//-----------------------------------------------------
import java.util.Vector;
public class TestArray {
public static void main(String[] agrs) {

// I only want to get an Array from the Vector v
Vector v = SomeClass.getVector();

// I can make sure the object type is correct
// I have checked every object in v is instanceof SomeClass
// [method1] and [method2] both throw
ClassCastException
SomeClass[] sc1 = (SomeClass[]) v.toArray(); // [method 1]
SomeClass[] sc2 = (SomeClass[]) toArray2(v); // [method 2]

// I have to code like this, and no exception any more.
Why?
SomeClass[] sc3 = new EmMessage[v.size()]; // [method 3]
for (int i = 0; i < v.size(); i++) {
sc4 = (SomeClass) v.elementAt(i);
}
}

public static Object[] toArray2(Vector vector) {
if (vector == null) {
return new Object[0];
}
Object[] obs = new Object[vector.size()];
for (int i = 0; i < obs.length; i++) {
obs = vector.elementAt(i);
}
return obs;
}

}

 

[Roedy Green]

SomeClass[] sc1 = (SomeClass[]) v.toArray(); // [method 1]

You are using toArray improperly.. See
http://mindprod.com/jgloss/array.html

What you are doing will get you an Object[] which cannot be cast to
SomeClass[].

 

[Richard Wheeldon]

SomeClass[] sc1 = (SomeClass[]) v.toArray(); // [method 1]

This will return an array of type Object[]. You can't cast an array
of type Object[] to an array of type SomeClass[] regardless of
whether every element is an instanceof SomeClass or not.

If you want to do this, you need to provide toArray an example of
the type of array you want to create.
Try:
SomeClass[] sc1 = (SomeClass[])v.toArray(new SomeClass[0]);

If you're doing this a lot, replace new SomeClass[0] with a reference
to some previously constructed array,

Richard

 

[castillo.bryan]

Note: If you allocate the right size for the array, the toArray method
will not have to allocate another array.

SomeClass[] sc1 = (SomeClass[])v.toArray(new SomeClass[v.size()]);

 

[Stefan Schulz]

Note: If you allocate the right size for the array, the toArray method
will not have to allocate another array.

SomeClass[] sc1 = (SomeClass[])v.toArray(new SomeClass[v.size()]);

It will also save a few very expensive reflection calls, so this idom is
almost always the better choice.