Different scenarios causing NoSuchElementException in Java

An exception is a problem that occurs during program execution (runtime error). When an exception occurs, the program will terminate abruptly, and the code after the line where the exception occurred will never be executed. Each exception is represented by its own class.

NosuchElement exception

This is a runtime exception, which occurs during execution.

If you try to access an element from an empty object, or use the accessor methods of Enumeration, Iterator, or tokenizer (such as next() or nextElement()) to access the content of a collection, array, or other objects, attempting to get the next element after reaching the end of the object (collection, array, or other objects) will generate NoSuchElementException.

Scenario

The nextElement() method of Enumeration-VectorHashTables and other collections have a method named elements() that returns an Enumeration (interface) object containing all elements of the collection.

Using this object, elements can be obtained one by one using the nextElement() method.

If this method is called on an empty collection, or if NoSuchElementException is generated after reaching the end of the collection, NoSuchElementException will be generated at runtime.

Example

import java.util.Enumeration;
import java.util.Vector;
public class EnumExample {
　　　public static void main(String args[]) {
　　　　　　//Instantiate the vector
　　　　　　Vector<Integer> vec = new Vector<Integer>( );
　　　　　　//Fill the vector
　　　　　　vec.add(1254);
　　　　　　vec.add(4587);
　　　　　　//Using enumeration to retrieve elements
　　　　　　Enumeration<Integer> en = vec.elements();
　　　　　　System.out.println(en.nextElement());
　　　　　　System.out.println(en.nextElement());
　　　　　　//retrieving the next element after reaching the end
　　　　　　System.out.println(en.nextElement());
　　　}
}

runtime error

1254
4587
Exception in thread "main" java.util.NoSuchElementException: Vector Enumeration
　　　at java.util.Vector$1.nextElement(Unknown Source)
　　　at MyPackage.EnumExample.main(EnumExample.java:18)

The nextElement() and nextToken() methods of StringTokenizer -The StringTokenizer class accepts String and delimiter as parameters in one of its constructors, splitting the given String into several small tokens each time the given delimiter appears.

The nextToken() and nextElement() methods of this type return the next token from the token generator. If these methods are called on an empty Tokenizer object, or if NoSuchElementException is called at the end, a NoSuchElementException will be generated at runtime.

Example

import java.util.StringTokenizer;
public class StringTokenizerExample{
　　　public static void main(String args[]) {
　　　　　　String str = "Hello how are you";
　　　　　　//instantiate StringTokenizer class
　　　　　　StringTokenizer tokenizer = new StringTokenizer(str, " ");
　　　　　　//print all tokens
　　　　　　System.out.println(tokenizer.nextToken());
　　　　　　System.out.println(tokenizer.nextToken());
　　　　　　System.out.println(tokenizer.nextToken());
　　　　　　System.out.println(tokenizer.nextToken());
　　　　　　//retrieving the next token after reaching the end
　　　　　　tokenizer.nextToken();
　　　　　　tokenizer.nextElement();
　　　}
}

runtime error

Hello
how
are
you
Exception in thread "main" java.util.NoSuchElementException
　　　at java.util.StringTokenizer.nextToken(Unknown Source)
　　　at MyPackage.StringTokenizerExample.main(StringTokenizerExample.java:16)

Iterator's next() method -Java provides Iterator and ListIterator classes to retrieve elements of collection objects. The next() method of Iterator and ListIterator returns the next element of the collection.

If these methods are called on an empty collection or NoSuchElementException is called at the end, a runtime exception will be generated.

Similarly, if this method is called on an empty object or at its declaration position, the ListIterator's previous() method will return the previous element of the collection and generate NoSuchElementException at runtime.

Example

import java.util.ArrayList;
import java.util.Iterator;
public class NextElementExample{
　　　public static void main(String args[]) {
　　　　　　//Instantiate an ArrayList object
　　　　　　ArrayList<String> list = new ArrayList<String>();
　　　　　　//Fill the ArrayList
　　　　　　list.add("apples");
　　　　　　list.add("mangoes");
　　　　　　list.add("oranges");
　　　　　　//Get the Iterator object of ArrayList
　　　　　　Iterator it = list.iterator();
　　　　　　System.out.println(it.next());
　　　　　　System.out.println(it.next());
　　　　　　System.out.println(it.next());
　　　　　　//retrieving the next element after reaching the end
　　　　　　it.next();
　　　}
}

runtime error

apples
mangoes
oranges
Exception in thread "main" java.util.NoSuchElementException
　　　at java.util.ArrayList$Itr.next(Unknown Source)
　　　at MyPackage.NextElementExample.main(NextElementExample.java:19)

Example (previous() method)

import java.util.ArrayList;
import java.util.ListIterator;
public class NextElementExample{
　　　public static void main(String args[]) {
　　　　　　//Instantiate an ArrayList object
　　　　　　ArrayList<String> list = new ArrayList<String>();
　　　　　　//Fill the ArrayList
　　　　　　list.add("apples");
　　　　　　list.add("mangoes");
　　　　　　list.add("oranges");
　　　　　　//Get the Iterator object of ArrayList
　　　　　　ListIterator<String> it = list.listIterator();
　　　　　　it.next();
　　　　　　it.next();
　　　　　　it.next();
　　　　　　System.out.println(it.previous());
　　　　　　System.out.println(it.previous());
　　　　　　System.out.println(it.previous());
　　　　　　System.out.println(it.previous());
　　　}
}

Output Result

oranges
mangoes
apples
Exception in thread "main" java.util.NoSuchElementException
　　　at java.util.ArrayList$ListItr.previous(Unknown Source)
　　　at MyPackage.NextElementExample.main(NextElementExample.java:22)