why is iterator object not created with new keyword for list collection in Java

Question

I came across this bit of code to remove strings of even length from given Linked list I don't understand why the iterator object itr not instantiated with new keyword. here is the code..

public static void removeEvenLength(List<String> list) {
     Iterator<String> itr= list.iterator();
     while (itr.hasNext()) {
         String element=itr.next();
         if (element.length()%2==0) {
             i.remove();
     }
   }
}       

Does it mean here, that the iterator method is static and it just returns a new iterable object with list as its field . can someone provide with me one or more examples where similar way of instantiating is encountered in Java other than singleton constructors I suppose. Thank you

Answer 1

Does it mean here, that the iterator method is static and it just returns a new iterable object with list as its field.

No, it's an instance method. It just returns a reference to an Iterator<String> . So the body of the iterator() method is likely to contain a new statement (although it's possible that it in turn calls on to something else). Let's take it away from iterators and generics for now - a similar situation is:

class Bar {}

class Foo {
    Bar createBar() {
        return new Bar();
    }
}

public class Test {
    public static void main(String[] args) {
        Foo foo = new Foo();
        Bar bar = foo.createBar();
    }
}

Same pattern: an instance method which returns a new instance of a different type.

Answer 2

Not every object is created explicitly with a new keyword. A method can internally create a new object, do some things to it, and return it.

Depending on the type of List the iterator is usually a private inner class, called Itr in the ArrayList. It is instantiated in iterator( . For the ArrayList example, that method reads as follows:

public Iterator<E> iterator() {
    return new Itr();
}

Other classes implementing List can either use a different private inner class, or may, in certain (non-jre, usually) implementations use an anonymous class.

Answer 3

It's not instantiated with the new operator because list.iterator is not a type, but a method that returns an object that is instantiated within the method. it's merely assigned to the return value of that method.