This is an example of how to obtain an ArrayList ListIterator. The ListIterator is an iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator’s current position in the list.
Obtaining an ArrayList ListIterator implies that you should:
- Create a new ArrayList.
- Populate the arrayList with elements, using
add(E e)API method of ArrayList. - In order to get the ListIterator call
listIterator()API method of ArrayList. - Use
hasNext()andnext()methods of ListIterator for forward iteration over the arrayList elements. - Use
hasPrevious()andprevious()methods of ListIterator for backward iteration over the arrayList elements. - Invoke
nextIndex()andpreviousIndex()methods to return next and previous index from the current position in the arrayList. - Invoke
remove()method to remove from the list the last element that was returned bynext()orprevious()methods. - Invoke
set(E e)method to replace the last element returned bynext()orprevious()methods with the specified element.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
import java.util.ArrayList;
import java.util.ListIterator;
public class ArrayListListIteratorExample {
public static void main(String[] args) {
// Create an ArrayList and populate it with elements
ArrayList arrayList = new ArrayList();
arrayList.add("element_1");
arrayList.add("element_2");
arrayList.add("element_3");
arrayList.add("element_4");
arrayList.add("element_5");
// The ListIterator object is obtained using listIterator() method
ListIterator it = arrayList.listIterator();
// For forward iteration over the collection elements we can use hasNext() and next() methods of ListIterator
System.out.println("Forward iteration :");
while(it.hasNext())
System.out.println(it.next());
// For backward iteration over the collection elements we can use hasPrevious() and previous() methods of ListIterator
System.out.println("Backward iteration :");
while(it.hasPrevious())
System.out.println(it.previous());
// nextIndex and previousIndex return next and previous index from the current position in the list
System.out.println("Previous Index is : " + it.previousIndex());
System.out.println("Next Index is : " + it.nextIndex());
// We get the next element in forward order
System.out.println("Next element is : " + it.next());
// nextIndex and previousIndex return next and previous index from the current position in the list
System.out.println("Previous Index is : " + it.previousIndex());
System.out.println("Next Index is : " + it.nextIndex());
// Add an element just before the next element
it.add("element_6");
System.out.println("After inserting element_6, ArrayList contains : ");
for(int i = 0; i < arrayList.size(); i++)
System.out.println(arrayList.get(i));
// We get the next element in forward order
System.out.println("Next element is : " + it.next());
// void remove() method removes the last element returned by next or previous methods
it.remove();
System.out.println("After removing element_2, ArrayList contains : ");
for(int i = 0; i < arrayList.size(); i++)
System.out.println(arrayList.get(i));
// We get the next element in forward order
System.out.println("Next element is : " + it.next());
/*
void set(Object o) method replaces the last element returned
by next or previous methods. The set method can only be called
if neither add or remove methods are called after last call of
next or previous methods
*/
it.set("element_7");
System.out.println("After replacing element_3, ArrayList contains : ");
for(int i = 0; i < arrayList.size(); i++)
System.out.println(arrayList.get(i));
}
}
Output:
Forward iteration :
element_1
element_2
element_3
element_4
element_5
Backward iteration :
element_5
element_4
element_3
element_2
element_1
Previous Index is : -1
Next Index is : 0
Next element is : element_1
Previous Index is : 0
Next Index is : 1
After inserting element_6, ArrayList contains :
element_1
element_6
element_2
element_3
element_4
element_5
Next element is : element_2
After removing element_2, ArrayList contains :
element_1
element_6
element_3
element_4
element_5
Next element is : element_3
After replacing element_3, ArrayList contains :
element_1
element_6
element_7
element_4
element_5
This was an example of how to obtain an ArrayList ListIterator in Java.
