NoSuchElementException in Java
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Overview
NoSuchElementException() is an exception thrown in Java by the next() or the nextElement method(). This is thrown when there is no impending element left in an enumeration. It is often shown when the user is trying to access the elements of an empty object, or when trying to get the subsequent element in a collection of objects which has already been traversed till the end.
Introduction
nosuchelementexception() is a runtime exception and occurs at the time of execution of the code. It is an unchecked exception, which means that is not checked at compile time. Errors and runtime exceptions are categorized as unchecked exceptions.
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Declaration
The exception is declared in the following manner, followed by the source of the error.
Constructor's Summary
| Constructor | Description |
|---|---|
| NoSuchElementException() | This method constructs a NoSuchElementException free from any error message |
| NoSuchElementException(String s) | It constructs a NoSuchElementException. It contains a message string s saved as a reference for the error for later retrieval by the getMessage method |
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Constructor in Java
A constructor in Java is a block of code similar to a method. When a new instance of the class is created, it is called. The object's memory is allocated when the function constructor is called. It is a type of method that is used to initialize an object.
At least one constructor is called every time an object is created with the new() keyword.
If there is no constructor in the class, it calls the constructor. In this case, the online Java compiler automatically provides a default constructor.
In Java, there are two kinds of constructors: no-arg constructors and parameterized constructors.
Defining a constructor is subject to three rules: The constructor's name must be the same as the name of the class. There must be no explicit return type in a Constructor. An abstract, static, final, or synchronized Java constructor is not allowed.
Methods of NoSuchElementException()
| Method | Description |
|---|---|
| NoSuchElementException() | It constructs a NoSuchElementException method without a string error message. |
| NoSuchElementException (String s) | It constructs a NoSuchElementException method with a message string s saved as a reference to the error for retrieval later by the getMessage method. The string s contains the name of the class that causes the error. |
What Causes java.util.NoSuchElementException()
The NoSuchElementException is thrown by the nextElement() method of an Enumeration, indicating that there are no more elements in the enumeration. The following methods throw the NoSuchElementException:
- nextElement() of Enumeration interface
- next() of NamingEnumeration interface
- nextElement() of StringTokenizer class
- next() of Iterator interface
One of the most typical causes of the NoSuchElementException is when we iterate over an empty Set. We may avoid this exception by adding a check before iterating through the set. While iterating, check every time that an element is present in the set and then do the following-
This method ensures that any element, if it exists, is accessed.
Examples of NoSuchElementException()
Example 1
In the following example, we are attempting to access a HashMap via the Iterator class's accessor method next(), but because the HashMap is empty, we will receive a NoSuchElementException.
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Java Program to Demonstrate the Occurrence of NoSuchElementException()
Example 2
In the Following Example, We're Attempting to Use an Enumerator to Access an Element of an Empty Vector Object.
How to Fix java.util.NoSuchElementException?
Almost all classes whose accessor methods throw NoSuchElementException provide a way to determine whether the object has more elements or not. To avoid this NoSuchElementException, we must always call --
Iterator.hasNext() or Enumeration.hasMoreElements() or hasMoreToken() method before calling next( ) or nextElement or nextToken() method.
The below examples demonstrate how NoSuchElementException can be fixed:
Example 1
Java Program that Uses hasNext to Prevent the Occurrence of NoSuchElementException()
The code shown above demonstrates the use of the hasNext() method. This allows the user to first check if a successive element is present and then only use the .next() method to avoid the NoSuchElementException().
Example 2
Here is a Java Program that Uses hasMoreElements to Prevent the Occurrence of NoSuchElementException().
The code shown above demonstrates the use of the hasMoreelements() method. This allows the user to first check if a successive, vectorial object is present and then only use the .next() method to avoid the NoSuchElementException().
Conclusion
- NoSuchElementException is an exception thrown in Java by the next() or the nextElement method()
- It is often shown when the user is trying to access the elements of an empty object, or when trying to get the subsequent element in a collection of objects which has already been traversed till the end.
- It is a runtime, unchecked exception.
- Iterator.hasNext() or Enumeration.hasMoreElements() or hasMoreToken() method before calling next( ) or nextElement or nextToken() method could be used to avoid NoSuchElementException.
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