将对象的数组列表转换为同一对象的数组时，为什么会出现 ClassCastException？

Question

So I'm not too experienced with these sort of things, and its also been a long day so I'm probably missing something obvious, but this is what is causing my error. Here is the error message in its entirety along with the lines that cause the error.

Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [LenumAssignment.Student; ([Ljava.lang.Object; is in module java.base of loader 'bootstrap'; [LenumAssignment.Student; is in unnamed module of loader 'app')

ArrayList<Student> s = nameObtain();
Student[] students = (Student[]) s.toArray();

Answer 1

Method List::toArray() returns Object[] which cannot be simply cast to Student[] (explained here )

So you have two three options:

1. Get Object[] arr and cast its elements to Student
2. Use typesafe List::toArray(T[] arr)
3. Use typesafe Stream::toArray method.

List<Student> list = Arrays.asList(new Student(), new Student(), new Student());
Object[] arr1 = list.toArray();
        
for (Object a : arr1) {
    System.out.println("student? " + (a instanceof Student) + ": " + (Student) a);
}
        
Student[] arr2 = list.toArray(new Student[0]);
        
System.out.println(Arrays.toString(arr2));

Student[] arr3 = list.stream().toArray(Student[]::new);
System.out.println(Arrays.toString(arr3));