Arrays.asList() doubt?

Question

People say that asList method convert the array into list and its not copying, so every change in 'aList' will reflect into 'a'. So add new values in 'aList' is illegal, since array have fixed size.

But, asList() method returns ArrayList<T>. How the compiler differentiates line 3 from 5. Line 3 gives me exception (UnsupportedOperationException).

        String[] a = {"a","b","c","d"};//1
        List<String> aList =  Arrays.asList(a);//2
        aList.add("e");//3
        List<String> b = new ArrayList<String>();//4
        b.add("a");//5

Answer 1

This List implementation you receive from Arrays.asList is a special view on the array - you can't change it's size.

The return type of Arrays.asList() is java.util.Arrays.ArrayList which is often confused with java.util.ArrayList. Arrays.ArrayList simply shows the array as a list.