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<div dir="ltr" style="text-align: justify;" trbidi="on">An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator&#8217;s current position in the list. A <b><i>ListIterator </i></b>has no current element; its cursor position always lies between the element that would be returned by a call to <b><i>previous()</i></b> and the element that would be returned by a call to <i><b>next()</b></i>.</div>
<p><b>Accessing a <i>Collection</i></b><br />
To access, modify or remove any element from any collection we need to first find the element, for which we have to cycle throught the elements of the collection. There are three possible ways to cycle through the elements of any collection.</p>
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<ul style="text-align: left;">
<li>Using <i><b>Iterator </b></i>interface</li>
<li>Using <i><b>ListIterator </b></i>interface</li>
<li>Using <i><b>for-each</b></i> loop</li>
</ul>
<p><b>Accessing elements using <i>Iterator</i>:</b><br />
Iterator Interface is used to traverse a list in forward direction, enabling you to remove or modify the elements of the collection. Each collection classes provide iterator() method to return an iterator.<br />
<b>The Methods Declared by Iterator:</b></p>
<table class="src" style="-webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: #f7f7f7; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); color: black; font-family: Helvetica, Arial, sans-serif; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; margin: 8px 0px; orphans: auto; padding: 0px; text-align: start; text-indent: 0px; text-transform: none; vertical-align: top; white-space: normal; widows: auto; width: 560px; word-spacing: 0px;">
<tbody style="margin: 0px; padding: 0px;">
<tr style="margin: 0px; padding: 0px;">
<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">SN</th>
<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">Methods with Description</th>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">1</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">boolean hasNext( )</b></i><br />
Returns true if there are more elements. Otherwise, returns false.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">2</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">Object next( )</b></i><br />
Returns the next element. Throws <i><b>NoSuchElementException </b></i>if there is not a next element.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">3</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">void remove( )</b></i><br />
Removes the current element. Throws <i><b>IllegalStateException </b></i>if an attempt is made to call<b><i> remove( )</i></b> that is not preceded by a call to<i><b> next( )</b></i>.</td>
</tr>
</tbody>
</table>
</div>
<pre class="highlight" name="code">import java.util.*; 
class TestIterator 
{ 
 public static void main(String[] args) 
 { 
 ArrayList ar = new ArrayList(); 
 ar.add("dinesh"); 
 ar.add("anamika"); 
 ar.add("adesh"); 
 ar.add("vinesh"); 
 
 Iterator it = ar.iterator(); //Declaring Iterator 
 while(it.hasNext()) 
 { 
 System.out.print(it.next()+" "); 
 } 
 } 
} 
</pre>
<p><b>output:</b></p>
<div class="separator" style="clear: both; text-align: center;"><img border="0" src="https://dineshonjava.com/wp-content/uploads/2013/05/listiterator.png"/></div>
</div>
<p><b>Accessing element using <i>ListIterator</i>:</b><br />
<i><b>ListIterator </b></i>Interface is used to traverse a list in both forward and backward direction. It is available to only those collections that implement the List Interface.</p>
<pre class="highlight" name="code">import java.util.*; 
class TestIterator 
{ 
 public static void main(String[] args) 
 { 
 ArrayList ar = new ArrayList(); 
 ar.add("dinesh"); 
 ar.add("anamika"); 
 ar.add("adesh"); 
 ar.add("vinesh"); 
 
 ListIterator litr = ar.listIterator(); 
 while(litr.hasNext()) //In forward direction 
 { 
 System.out.print(litr.next()+" "); 
 } 
 System.out.println(); 
 while(litr.hasPrevious()) //In backward direction 
 { 
 System.out.print(litr.previous()+" "); 
 } 
 } 
} 
</pre>
<p><b>Output:</b></p>
<div class="separator" style="clear: both; text-align: center;"><img border="0" src="https://dineshonjava.com/wp-content/uploads/2013/05/listiterator2.png"/></div>
<p><b><br />
</b> <b>The Methods Declared by <i>ListIterator</i>:</b></p>
<table class="src" style="-webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: #f7f7f7; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); color: black; font-family: Helvetica, Arial, sans-serif; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; margin: 8px 0px; orphans: auto; padding: 0px; text-align: start; text-indent: 0px; text-transform: none; vertical-align: top; white-space: normal; widows: auto; width: 560px; word-spacing: 0px;">
<tbody style="margin: 0px; padding: 0px;">
<tr style="margin: 0px; padding: 0px;">
<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">SN</th>
<th style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px; text-align: left;">Methods with Description</th>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">1</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">void add(Object obj)</b></i><br />
Inserts obj into the list in front of the element that will be returned by the next call to next( ).</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">2</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">boolean hasNext( )</b></i><br />
Returns true if there is a next element. Otherwise, returns false.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">3</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">boolean hasPrevious( )</b></i><br />
Returns true if there is a previous element. Otherwise, returns false.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">4</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">Object next( )</b></i><br />
Returns the next element. A <i><b>NoSuchElementException </b></i>is thrown if there is not a next element.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">5</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">int nextIndex( )</b></i><br />
Returns the index of the next element. If there is not a next element, returns the size of the list.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">6</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">Object previous( )</b></i><br />
Returns the previous element. A <i><b>NoSuchElementException </b></i>is thrown if there is not a previous element.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">7</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><b style="margin: 0px; padding: 0px;">i<i>nt previousIndex( )</i></b><br />
Returns the index of the previous element. If there is not a previous element, returns -1.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">8</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">void remove( )</b></i><br />
Removes the current element from the list. An <i><b>IllegalStateException </b></i>is thrown if remove( ) is called before next( ) or previous( ) is invoked.</td>
</tr>
<tr style="margin: 0px; padding: 0px;">
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;">9</td>
<td style="border-collapse: collapse; border: 1px solid rgb(214, 214, 214); margin: 0px; padding: 5px;"><i><b style="margin: 0px; padding: 0px;">void set(Object obj)</b></i><br />
Assigns obj to the current element. This is the element last returned by a call to either next( ) or previous( ).</td>
</tr>
</tbody>
</table>
<p><b>Using <i>for-each </i>loop</b><br />
<i><b>for-each</b></i> version of for loop can also be used for traversing each element of a collection. But this can only be used if we don&#8217;t want to modify the contents of a collection and we don&#8217;t want any reverse access. ;<br />
<i><b>for-each</b></i> loop can cycle through any collection of object that implements <i><b>Iterable </b></i>interface.</div>
<pre class="highlight" name="code">import java.util.*; 
class TestIterator 
{ 
 public static void main(String[] args) 
 { 
 ArrayList ar = new ArrayList(); 
 ar.add("dinesh"); 
 ar.add("anamika"); 
 ar.add("adesh"); 
 ar.add("vinesh"); 
 
 for(Object str : ls) 
 { 
 System.out.print(str+" "); 
 } 
 } 
} 
</pre>
<p><b>output:</b></p>
<div class="separator" style="clear: both; text-align: center;"><img border="0" src="https://dineshonjava.com/wp-content/uploads/2013/05/listiterator.png"/></div>
</div>
<p></p>
<div style="background-color: #f2f9fc; border-radius: 3px; border: 1px solid #c9e6f2; line-height: 1.45; padding: 16px;">
<b>Java Collections Tutorial</b></p>
<ol style="text-align: left;">
<li><b><a href="https://dineshonjava.com/arraylist-class-in-java-collection/">ArrayList class</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedlist-class-in-collection/">LinkedList class</a></b></li>
<li><b><a href="https://dineshonjava.com/hashset-class-in-collection/">HashSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedhashset-class-in-collection/">LinkedHashSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/treeset-classin-collection/">TreeSet class</a></b></li>
<li><b><a href="https://dineshonjava.com/difference-between-hashset-and-treeset/">Difference between TreeSet &; HashSet</a></b></li>
<li><b><a href="https://dineshonjava.com/map-interface-in-collection/">Map interface</a></b></li>
<li><b><a href="https://dineshonjava.com/hashmap-class-in-collection-framework/">HashMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/how-does-java-hashmap-work-internally/">How does work HashMap?</a> </b></li>
<li><b><a href="https://dineshonjava.com/difference-between-treemap-vs-hashmap/">Difference between TreeMap vs HashMap</a></b></li>
<li><b><a href="https://dineshonjava.com/linkedhashmap-class-in-collection/">LinkedHashMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/treemap-class-in-collection-framework/">TreeMap class</a></b></li>
<li><b><a href="https://dineshonjava.com/hashtable-class-in-collection-framework/">Hashtable class</a></b></li>
<li><b><a href="https://dineshonjava.com/difference-between-hashmap-and/">Difference between HashMap and HashTable in Java</a></b></li>
<li><b><a href="https://dineshonjava.com/sorting-in-collection-framework/">Sorting</a></b></li>
<li><b><a href="https://dineshonjava.com/java-comparable-and-comparator/">Comparable interface</a></b></li>
</ol>
</div>
<p></p>
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