Collections.emptyList() returns a List<Object>?

The issue you're encountering is that even though the method emptyList() returns List<T>, you haven't provided it with the type, so it defaults to returning List<Object>. You can supply the type parameter, and have your code behave as expected, like this:

public Person(String name) {  this(name,Collections.<String>emptyList());}

Now when you're doing straight assignment, the compiler can figure out the generic type parameters for you. It's called type inference. For example, if you did this:

public Person(String name) {  List<String> emptyList = Collections.emptyList();  this(name, emptyList);}

then the emptyList() call would correctly return a List<String>.

You want to use:

Collections.<String>emptyList();

If you look at the source for what emptyList does you see that it actually just does a

return (List<T>)EMPTY_LIST;

the emptyList method has this signature:

public static final <T> List<T> emptyList()

That <T> before the word List means that it infers the value of the generic parameter T from the type of variable the result is assigned to. So in this case:

List<String> stringList = Collections.emptyList();

The return value is then referenced explicitly by a variable of type List<String>, so the compiler can figure it out. In this case:

setList(Collections.emptyList());

There's no explicit return variable for the compiler to use to figure out the generic type, so it defaults to Object.