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What is the cause of NoSuchElementException and how can we fix it in java?
What is the cause of NoSuchElementException and how can we fix it in java?
An exception is an issue (run time error) occurred during the execution of a program. When an exception occurred the program gets terminated abruptly and, the code past the line that generated the exception never gets executed. Each exception is represented by its respective class.
Cause for NosuchElementException
This is a Runtime exception i.e. it occurs at the execution time.
While accessing the contents of a collection, array or other objects using the accessor methods of an Enumeration, Iterator or, tokenizer, such as next() or nextElement(), if you try to get the elements from an empty object, or if you try to get the next element after reaching the end of the object (collection, array, or other) a NoSuchElementException is generated.
For example,
- If you call the nextElement() method of the Enumeration class on an empty enumeration object or, if the current position is at the end of the Enumeration, a NosuchElementException is generated at run time.
- If you nextElement() and nextToken() methods of the StringTokenizer class on an empty StringTokenizer object or, if the current position is at the end of the StringTokenizer, a NosuchElementException is generated at run time.
- If the next() methods of the Iterator or ListIterator classes, invoked on an empty Iterator/ListIterator or, if the current position is at the end, the Iterator/listIterator NosuchElementException is generated at run time.
- Similarly if the previous() method of the ListIterator class is invoked on an empty ListIterator object, or if the current position is the start of the ListIterator a NosuchElementException is generated at run time.
Example
import java.util.StringTokenizer;
public class StringTokenizerExample{
public static void main(String args[]) {
String str = "Hello how are you";
//Instantiating the StringTokenizer class
StringTokenizer tokenizer = new StringTokenizer(str, " ");
//Printing all the tokens
System.out.println(tokenizer.nextToken());
System.out.println(tokenizer.nextToken());
System.out.println(tokenizer.nextToken());
System.out.println(tokenizer.nextToken());
//Getting 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)
Handling/Fixing NosuchElementException
Almost all the classes whose accessor method causes NoSuchElementException contains their respective methods to verify whether the object (collection, tokenizer etc.) contains more elements.
For example −
- The Enumeration class contains a method named hasMoreElements() which returns true if the current object contains more elements after the current position (else it returns false).
- The StringTokenizer class contains methods named hasMoreTokens() and hasMoreElements() which returns true if the current object contains more elements after the current position (else it returns false).
- The Iterator class contains hasNext() method this also returns true if the current iterator contains more elements next to the current position (else it returns false).
- The ListIterator class contains hasPrevious() method this also returns true if the current iterator contains more elements previously to the current position (else it returns false).
In the while loop verify whether the respective object contains more elements using these methods, print/access elements only, if the condition is true. This prevents the access of elements using accessor methods when there are no elements in the object or, if it reaches the end.
hasMoreElements() method of the Enumeration class
import java.util.Enumeration;
import java.util.Vector;
public class EnumExample {
public static void main(String args[]) {
//instantiating a Vector
Vector<Integer> vec = new Vector<Integer>( );
//Populating the vector
vec.add(1254);
vec.add(4587);
//Retrieving the elements using the Enumeration
Enumeration<Integer> en = vec.elements();
while(en.hasMoreElements()) {
System.out.println(en.nextElement());
}
}
}Output
1254 4587
nextMoreTokens() method of the StringTokenizer class −
import java.util.StringTokenizer;
public class StringTokenizerExample{
public static void main(String args[]) {
String str = "Hello how are you";
//Instantiating the StringTokenizer class
StringTokenizer tokenizer = new StringTokenizer(str, " ");
//Printing all the tokens
while(tokenizer.hasMoreTokens()) {
System.out.println(tokenizer.nextToken());
}
}
}Output
Hello how are you
hasNext() method of the Iterator class −
import java.util.ArrayList;
import java.util.Iterator;
public class NextElementExample{
public static void main(String args[]) {
//Instantiating an ArrayList object
ArrayList<String> list = new ArrayList<String>();
//populating the ArrayList
list.add("apples");
list.add("mangoes");
list.add("oranges");
//Getting the Iterator object of the ArrayList
Iterator it = list.iterator();
while(it.hasNext()) {
System.out.println(it.next());
}
}
}Output
apples mangoes oranges
hasPrevious() method of the ListIterator class −
import java.util.ArrayList;
import java.util.ListIterator;
public class NextElementExample{
public static void main(String args[]) {
//Instantiating an ArrayList object
ArrayList<String> list = new ArrayList<String>();
//populating the ArrayList
list.add("apples");
list.add("mangoes");
list.add("oranges");
//Getting the Iterator object of the ArrayList
ListIterator<String> it = list.listIterator();
while(it.hasNext()) {
it.next();
}
while(it.hasPrevious()) {
System.out.println(it.previous());
}
}
}Output
oranges mangoes apples
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