我是否必须将Java中已经通用的数组转换为通用类型

Question

Sorry for the wording but maybe code can be understood easier

public class Generic<E> implements List<E>
{
    private static final int defaultSize = 10; //Default size
    private int maxSize; //Maximum size of list
    private int listSize; //Current # of items in list
    private int curr; //Position of current element
    private E[] listArray; //Array holding list elements
    Generic()
    {
        this(defaultSize);
    }
    /**
    * Create a new list object
    * @param siz Max # of elements list can contain
    */
    @SuppressWarnings("unchecked") //generic array allocation
    Generic(int size)
    {
        maxSize = size;
        listSize = curr = 0;
        listArray = (E[]) new Object[size]; //create listArray

My two questions are these:

1. The last line, when I create the list as an object of size size , why do I have to cast it as a generic array when it's initialized as a generic array already?

2. Can the @SuppressWarnings("unchecked"); be explained? What it does I can see, but I have never seen the @SuppressWarnings on any of the pages in my Java book; how can we start with @ ??

Sidenote - this code is straight from my Data Structures book and I'm trying to break it down to understand it.

Answer 1

1. You have to recast it as E[] because of type erasure : at runtime, every generic is treated as Object . You can't initialize listArray as new E[] .
2. @SuppressWarnings is an annotation, basically extra information besides imperative code.

You have to supressed unchecked because otherwise the Java compiler will warn you when it encounters the potentially dangerous cast of Object[] to E[] .