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():

• Create an empty ArrayList
• Add elements to ArrayList.
• Create a listiterator using listIterator() method.

Listiteratoriterator = arrList.listIterator();

• Now get the required index using the below commands

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