Main methods in the ListIterator interface

In this post, we are going to see the main methods in the ListIterator interface, as well as their use. This adds some additional functionality and advantages over Iterator.

What is ListIterator?

ListIterator is an extension of Iterator that adds new functionality to iterate over lists. Obviously, it will inherit the main methods of Iterator and additionally incorporate some new ones that we will see below.

Main methods of use in the ListIterator interface.

To be able to use the ListIterator interface, we will start with a list and call the listIterator method.

List<String> numbers = List.of("1","2");
ListIterator<String> listIterator = numbers.listIterator(items.size());

hasNext() Method

The hasNext() method, which comes from the Iterator interface, is used to check if there is a next element in the collection.

while(listIterator.hasNext()) {
  ......
  System.out.println(it.next());
}

hasPrevious() method in ListIterator

The hasPrevious() method is the equivalent of hasNext() but in reverse, it checks if there is a previous element.

while(listIterator.hasPrevious()) {
    //do something
}

previous() in ListIterator

The previous() method retrieves the previous element from the ListIterator.

while(listIterator.hasPrevious()) {
    String previousElement = listIterator.previous();
}

Both hasPrevious() and previous() methods can iterate a collection in reverse order.

next() method

The next() method of a ListIterator allows us to move to the next element of the collection.

while(listIterator.hasNext()) {
  System.out.println(it.next());
}

nextIndex() method

The nextIndex() method of ListIterator indicates the index of the element that is returned by next().

String nextIndex = numbers.get(listIterator.nextIndex());

previousIndex() method

The previousIndex() method of ListIterator returns the index of the element when using previous().

String previousIndex = numbers.get(listIterator.previousIndex());

add() en ListIterator

The add() method in ListIterator allows us to add a new element just before the element returned by next() and after the element returned by previous().

listIterator.add("FOUR");

set() in ListIterator

The set() method allows us to replace the current element we are working with, i.e., we replace the element returned by the next() or previous() method call.

String nextElement = listIterator.next();
if( "1".equals(nextElement)) {
    listIterator.set("0");
}

remove()

To remove the current element in an Iterator, we use the remove() method.

while(listIterator.hasNext()) {
      Integer i = listIterator.next();
      if(i < 5) {
        listIterator.remove();
      }
    }