How do I create a List of generic arrays in Java?
I've written a class which accepts a generic type, and I'm trying to create an array list of generic arrays within it. I understand that Java can't create generic arrays, but I also know there are workarounds. Is there a way the below code can work, or am I barking up the wrong tree?
public class IterableContainer<开发者_运维知识库;T extends IterableItem> {
private T[] itemArray;
// how can i get this following line to work?
private List<T[]> items = new ArrayList<T[10]>();
public IterableContainer() {
... etc ...
Ignore past here - turns out it was an IDE issue. Left in for continuity of questions and answers.
EDIT:
This also doesn't work:
private List<T[]> items = new ArrayList<T[]>();
with the error:
Syntax error on token ">", VariableDeclaratorId expected after this token
"... barking up the wrong tree..., use a List<List<T>>
. Using raw arrays in Java is almost always a code smell, there is no reason not to use the proper collection classes.
It works just fine, you just can't use the T[10]
declaration as the length of an array doesn't affect its type.
i.e.
... = new ArrayList<T[]>();
Not saying it's a great idea, but it should be possible with the same restrictions on generic arrays as always. Creating stuff to put in your list will give you a headache.
private List<T[]> items = new ArrayList<T[]>();
works fine in my machine
When you say "I'm developing for mobile devices" ....are you targeting j2me? There is no support for generics in j2metargetng
This is a valid declaration in java (according to spec) and compiles just fine with javac as others have commented.
public class IterableContainer<T extends IterableItem> {
private T[] itemArray;
private List<T[]> items = new ArrayList<T[]>();// valid
..........
}
I believe the error you are seeing is not emitted from Eclipse, possibly coming from an Android SDK configured in Eclipse. If you create a Java Project in Eclipse, this code should work just fine. If you use this in an Android Project in Eclipse, you are likely to run into this one. I had this error when running this code from an Android project :
# guarantee(_name_index != 0 && _signature_index != 0) failed: bad constant pool index for fieldDescriptor
Sounds like you are restricted in an Android project, unfortunately.
You have not defined T in this code.
If you are creating a generic class, you need to write:
public class <T extends IterableItem> IterableContainer...
The next problem in your code is that you are trying to initilize items of ArrayList during its construction. It is impossible. You should rather write:
private List<T[]> items = new ArrayList<T[]>();
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