ArrayList and String[] AND Object[]

Question

I have searched this, but couldn't find what i need, so i created a new post. I hope to understand about this problem. Thanks.

ArrayList<String> arraylist= new ArrayList<String>();
arraylist.add("Nguyen");
arraylist.add("Viet");

String[] name={"Quan","Doan","Thi","Ha"};
arraylist.add(name);// error here 

ArrayList<Object> arraylist1=new ArrayList<Object>();
arraylist1.add("Nguyen");
arraylist1.add("Viet");
Object[] name1={"Quan","Doan","Thi","Ha"};
arraylist1.add(name1);// not error

Can someone explain that when i pass name into add() method then I get a error, but when i pass name1 into add() method, it works fine, why is it so...

Answer 1

arraylist is an ArrayList of String elements, so you can't add an array instance to it. arraylist1 is an ArrayList of Object elements, so you can add an array to it, since an array is an Object.

If you wish to add the individual elements of the arrays to the Lists, both add calls should be changed to addAll :

arrayList.addAll(Arrays.asList(name));
arraylist1.addAll(Arrays.asList(name1));

Answer 2

arraylist.add(name);// error here 

Error because name is an array. Not a String. You are trying to add a Array object to an ArrayList which accepts only Strings.

arraylist1.add(name1);// not error

No error because name1 is an Object array. In Java every class is an Object, even an array of Objects also an Object. Hence it accepted it as an Object. Though your name1 is an array of Objects, as a whole it is an Object itself first.