String[] 方法返回一个非空的 java

Question

I recently ported my eclipse project to IJ recently and my array randomizer returns following error

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 Constants.func.ranArr(func.java:42)

and

(String[]) i.toArray();in func.ranArr(String[])(filter not-null)

this is the code of the method

    public static String[] ranArr(String[] arr) {
        List<String> i = Arrays.asList(arr);
        Collections.shuffle(i);
        String[] r = (String[]) i.toArray();
        return r;
    }

How do I fix it, it worked in Eclipse

Answer 1

You can replace (String[]) i.toArray() by i.toArray(new String[0]) .

Answer 2

Because an ArrayList can store items of any type, internally it uses a Object[] to store the array's contents.

When you call toArray() , it simply returns a copy of that internal array, which is again an Object[] .

In fact, because of type erasure (the fact that an instance of a generic type doesn't know at runtime what type its type parameters are) the ArrayList can't do anything else.

As you know that you are storing Strings, you can use toArray(new String[0]) , as @Timur suggested.

That function will look at the type of the array you pass and create a new array with that type.