Error Generic Array Creation

Question

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  lt  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   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

User · Answer

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.

User · Answer

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

User · Answer

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 lt PCB gt  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

[java] Error: Generic Array Creation

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