Warning: [unchecked] unchecked cast. Generics

Question

I am encountering warnings of unchecked cast. I'm not sure how to resolve the warnings.

The compiler error seems to pick on list = (E[]) new IntKeyed [size];
Which is the code we are suppose to used letter for letter.
We are attempting to use Generics hence the "E".

So I figure I must have goofed somewhere in this code. When I looked up the error, it seemed to deal with ArrayLists , but I'm not using an ArrayList to my knowledge.

Maybe I should be ArrayLists ? Would changing that fix the warnings? I also have an issue with incomplete exception handling in my code. But I think that is isolated from the Array issue.

Any errors you can find will help point me in the right direction. Thanks.

public abstract class MyArrayList<E> implements IntKeyed
{

private final int DEFCAP = 50;
private int origCap;
private int numElements;
private E[] list;

public MyArrayList()
{
    origCap = DEFCAP;
    list = (E[]) new IntKeyed [origCap];    *******Error Here
}

public MyArrayList( int size ) throws Exception
{
    size = DEFCAP;
    if( size > 0 )
    {
        list = (E[]) new IntKeyed [size];    *******Error Here
        origCap = size;
    }
    else
    {
        throw new ArrayStoreException();
        System.out.println("List size is invalid");
    }
    list = (E[]) new IntKeyed [size];         *******Error Here
}

private void enlarge ()
{
    E[] larger = (E[]) new IntKeyed [list.length + origCap]; *******Error Here
    for( int i = 0; i < list.length; i++)
    {
        larger[i] = list[i];
    }
    list = larger;
}

When compiling with javac -Xlint:unchecked MyArrayList.java I get:

MyArrayList.java:29: warning: [unchecked] unchecked cast
    list = (E[]) new IntKeyed [origCap];
                 ^
required: E[]
found:    IntKeyed[]
where E is a type-variable:
E extends Object declared in class MyArrayList
MyArrayList.java:37: warning: [unchecked] unchecked cast
        list = (E[]) new IntKeyed [size];
                     ^
required: E[]
found:    IntKeyed[]
where E is a type-variable:
E extends Object declared in class MyArrayList
MyArrayList.java:45: warning: [unchecked] unchecked cast
    list = (E[]) new IntKeyed [size];
                 ^
 required: E[]
found:    IntKeyed[]
where E is a type-variable:
E extends Object declared in class MyArrayList
MyArrayList.java:117: warning: [unchecked] unchecked cast
    E[] larger = (E[]) new IntKeyed [list.length + origCap];
                       ^
required: E[]
found:    IntKeyed[]
where E is a type-variable:
E extends Object declared in class MyArrayList
MyArrayList.java:43: error: unreachable statement
        System.out.println("List size is invalid");
        ^
1 error
4 warnings

Answer 1

warnings is not a problem, problem is unreachable statement after throwing exception.

it should be this way:

System.out.println("List size is invalid");
throw new ArrayStoreException();

If your believe that your casts should work - add @SuppressWarnings("unchecked") on method or statement level(smaller scope is better). Compiler will not emit any messages, but you will still get exception in runtime if you casts are wrong.

Answer 2

Warning at list = (E[]) new IntKeyed [origCap]; practically means that generic E is being hardcoded as IntKeyed so whatever you pass for E , your list will always remain of type IntKeyed .

In your case, generic use doesn't seem to be suited as you are already implementing specific interface for this purpose.