Error: Generic Array Creation [duplicate]
I don't understand the error of Generic Array Creation.
First I tried the following: public PCB[] getAll() {
PCB[] res = new PCB[list.size()];
for (int i = 0; i < res.length; i++) {
res[i] = list.get(i);
}
list.clear();
return res;
}
Then I tried doing this:
PCB[] res = new PCB[100];
I must be missing something cause that seems right. I tried looking it up I really did. And nothing is clicking.
My question is: What can I do to fix this?
the error is :
.\Queue.java:26: generic array creation
PCB[]开发者_如何学Python res = new PCB[200];
^
Note: U:\Senior Year\CS451- file
uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error
Tool completed with exit code 1
You can't create arrays with a generic component type.
Create an array of an explicit type, like Object[]
, instead. You can then cast this to PCB[]
if you want, but I don't recommend it in most cases.
PCB[] res = (PCB[]) new Object[list.size()]; /* Not type-safe. */
If you want type safety, use a collection like java.util.List<PCB>
instead of an array.
By the way, if list
is already a java.util.List
, you should use one of its toArray()
methods, instead of duplicating them in your code. This doesn't get your around the type-safety problem though.
The following will give you an array of the type you want while preserving type safety.
PCB[] getAll(Class<PCB[]> arrayType) {
PCB[] res = arrayType.cast(java.lang.reflect.Array.newInstance(arrayType.getComponentType(), list.size()));
for (int i = 0; i < res.length; i++) {
res[i] = list.get(i);
}
list.clear();
return res;
}
How this works is explained in depth in my answer to the question that Kirk Woll linked as a duplicate.
Besides the way suggested in the "possible duplicate", the other main way of getting around this problem is for the array itself (or at least a template of one) to be supplied by the caller, who will hopefully know the concrete type and can thus safely create the array.
This is the way methods like ArrayList.toArray(T[])
are implemented. I'd suggest you take a look at that method for inspiration. Better yet, you should probably be using that method anyway as others have noted.
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