ClassCastException when declaring class generic as string-CodePudding

I have a GenericList class that must initialise an array with type but it force me to declare it as Object in compile time. When I declare the generic as String in Main, the program stops with ClassCastException when i assign the list.items to a variable called items, which compile time also recognise it as String[]. Error is like this:

Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [Ljava.lang.String; ([Ljava.lang.Object; and [Ljava.lang.String; are in module java.base of loader 'bootstrap')
    at com.advanced.Main.main(Main.java:51)".

Why and how to solve this? Thank you.

public class GenericList<T> {   
    public T[] items = (T[]) new Object[10];
    private int count;
    public void add(T item){
        items[count  ] = item;
    }
    public T get(int index){
        return items[index];
    }
    public T[] getItems() {
        return items;
    }
}

public class Main {

    public static void main(String[] args) {

        var list = new GenericList<String>();
        list.add("a");
        list.add("b");
        var items = list.items;
        for(var item: items){
            System.out.println(item);
        }
    }
}

CodePudding user response：

You must to inject explicitly the array constructor for T type.

E.g. move your new T[10] as

static class GenericList<T> {
    final public T[] items;
    private int count;

    public GenericList(IntFunction<T[]> arrayConstructor) {
        items = arrayConstructor.apply(10);
    }

And create the object injecting the constructor

var list = new GenericList<>(String []::new);

Now all works

a
b
null
null
null
null
null
null
null
null

(Note: with T[] items = (T[]) new Object[10] you are not creating a T array, you are creating an Object array casting to a T array, which is incorrect)