The previous index and the next index in an ArrayList can be retrieved using the PreviousIndex() and nextIndex() methods in the ListIterator interface. previousIndex() can also return -1 if it is at the top of the list.
Example:
Input: list = [2, 3, 6, 8] listiterator is at the beginning find previous index. Output: -1 Input: list = [2, 3, 6, 8] listiterator is at the beginning find next index.
Steps to use previousIndex() and nextIndex():
Listiteratoriterator = arrList.listIterator();
Syntax
iterator.previousIndex();
Returns: the index of the element to be returned in the next call to the previous one, or -1 if the list iterator is at the beginning of the list
Syntax
iterator.nextIndex();
Returns: the index of the element to return on the next call, or the size of the list if the list iterator is at the end of the list
Example
// Java program to get Previous and // next index using ListIterator import java.io.*; import java.util.ArrayList; import java.util.ListIterator; class PreviousAndNextIndex { public static void main(String[] args) { // create empty ArrayList ArrayList arrList = new ArrayList(); // add elements to the ArrayList arrList.add(5); arrList.add(10); arrList.add(15); arrList.add(20); arrList.add(25); arrList.add(30); // print the initial list System.out.println("Initial arraylist =>" + arrList); // initializing ListIterator ListIterator iterator = arrList.listIterator(); // initially iterator is the beginning so // previousIndex() will return -1 System.out.println("previous index =>" + iterator.previousIndex()); // from -1 moving iterator to the 1st index iterator.next(); iterator.next(); // now iterator is at 1st index // so nextIterator() will return 2 System.out.println("Next index =>" + iterator.nextIndex()); } }
Output:
Initial arraylist =>[5, 10, 15, 20, 25, 30] previous index =>-1 Next index =>2