Java Cast toArray Integer ClassCastException

Collection c = new ArrayList();
		Integer obj = new Integer(1);
		c.add(obj);

		// throw a ClassCastException
		Integer[] a = (Integer [])c.toArray();

		// fine
		Integer[] b = (Integer [])c.toArray(new Integer[c.size()]);

Exception in thread "main" java.lang.ClassCastException: java.base/[Ljava.lang.Object; cannot be cast to java.base/[Ljava.lang.Integer;