Introduction to Programming

Immutable without methods of()

To be fair, there are ways to create an immutable collection even without using the of() factory methods. Here is one way to do it:

List<String> iList =        Collections.unmodifiableList(new ArrayList<>() {{            add("s1");            add("s1");        }});//iList.set(0, "s0");       //UnsupportedOperationException//iList.add("s2");          //UnsupportedOperationExceptionSystem.out.println(iList);  //prints: [s1, s1]

The trick is not to have a reference to the original collection (the source of values) used to create the unmodifiable collection, so it cannot be used to change the underlying source. 

And here is another way to create an immutable collection without using the of() factory methods:

String[] source = {"s1", "s2"};List<String> ...