ListIterator in Java
Java has an interface ListIterator. It is an enhanced version of Iterator interface. The purpose of ListIterator is to iterate data in collections. If we use Iterator , then iteration is allowed only in forward direction. But if we use ListIterator iteration in both directions is possible.That is the difference between Iterator and ListIterator.
Methods in ListIterator.
Now , let us see the methods in ListIterator. There are 9 methods in ListIterator.
1)E next()
2)boolean hasNext()
3)void remove()
4)boolean hasPrevious()
5)E previous()
6)int nextIndex()
7) int previousIndex()
8)void set(E e)
9) void add(E e)
The first 3 methods are there in Iterator .Others are added in ListIterator.Now let us see an example.
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
public class IteratorSample {
List list = null;
public IteratorSample() {
list = new ArrayList();
}
public void addItems() {
list.add("cat");
list.add("dog");
list.add("cow");
}
public void displayItems() {
System.out.println("Forward");
ListIterator iterator = list.listIterator();
System.out.println("Iterating the list");
while (iterator.hasNext()) {
System.out.println(iterator.next().toString());
}
System.out.println("Reverse");
while (iterator.hasPrevious()) {
System.out.println(iterator.previous());
}
}
public static void main(String[] args) {
IteratorSample sample = new IteratorSample();
sample.addItems();
sample.displayItems();
}
}
The addeItems() method adds few Strings into an ArrayList.The displayItems() method creates a ListIterator object and by using that object iterating the ArrayList in forward and reverse directions.
Output
Forward
Iterating the list
cat
dog
cow
Reverse
cow
dog
cat
So if we need to iterate collections in both directions ListIterator is suitable.