Code Recipes Blog

In this post under Java, I will show with example how to iterate a list in both directions.

For iterating in both direction, we will take the help of “ListIterator” class.

We get an instance of “ListIterator” by calling “listIterator” method on a list.

Below is the code snippet, where “integerList” is a list of type parameter “Integer”

    ListIterator<Integer> listIterator = integerList.listIterator();

Once we obtain an instance of “ListIterator” we can use “hasNext” and “next” methods to move forward one item at a time.

We can also use “hasPrevious” and “previous” methods to move backward one item at a time.

Below is the complete main class for your reference.

Main class

1  package core.collection;
2  
3  import java.util.ArrayList;
4  import java.util.List;
5  import java.util.ListIterator;
6  
7  public class ListIteratorDemo {
8      public static void main(String[] args) {
9          List<Integer> integerList = new ArrayList<>(0);
10         integerList.add(1);
11         integerList.add(2);
12         integerList.add(3);
13         integerList.add(4);
14         integerList.add(5);
15         integerList.add(6);
16         integerList.add(7);
17         integerList.add(8);
18         integerList.add(9);
19         integerList.add(10);
20 
21         ListIterator<Integer> listIterator = integerList.listIterator();
22         System.out.println("Iterating forward");
23         while(listIterator.hasNext()) {
24             int data = listIterator.next();
25             System.out.print(data + ",");
26         }
27         System.out.println();
28         System.out.println("Iterating backward");
29         while(listIterator.hasPrevious()) {
30             int data = listIterator.previous();
31             System.out.print(data + ",");
32         }
33     }
34 }

In the above code, at line 9 I create a list of type parameter “Integer” named “integerList” and populated it.

At line 21, I obtain an instance of “ListIterator” by calling “listIterator” method on the “integerList”.

In the loop at line 23, I move forward using “hasNext” and “next” method and print the elements.

Similarly in the loop at line 29, I move backward using “hasPrevious” and “previous” method and print the elements.

In this way we can iterate a list in both directions.