Difficulty throwing NoSuchElementException in Java

Question

this is my first attempt to a code doubly linked program in java:

This is my implementation of getting an iterator to getall items in the doubly linkedlist

public Object next()  {
    if(list.getSize()==0){
     throw new NoSuchElementException();

    }else{ 
        current=current.getNext();
        return current.getItem();
    } 
}

Please dont laugh at me but whatever I try I am getting

Cannot find symbol : symbol class: NoSuchElementException

I tried creating a class NoSuchElementException.java which extends Exception

Then I get

unreported exception NoSuchElementException; must be caught or declared to be thrown throw new NoSuchElementException();

I tried changing code to :

public Object next() throws NoSuchElementException {

Then I get

next() in ElementsIterator cannot implement next() in java.util.Iterator; overridden method does not throw NoSuchElementException

Can anybody point to where I got wrong. If this is not sufficient info to resolve this issue, please do tell me.

Answer 1

You need to import java.util.NoSuchElementException instead of creating your own.

Answer 2

The compiler is giving you a pretty good explanation. You are providing an implementation of the next() method declared in Iterator, which has a signature of:

public Object next()

However, you have introduced your own checked exception called NoSuchElementException, which required that you change the method signature to:

public Object next() throws NoSuchElementException

Now you are no longer implementing the method declared in the interface. You've changed the signature.

Anyways, there are a couple ways you can fix this:

1. Change your NoSuchElementException class so that it inherits from RuntimeException instead of just Exception. Then you don't need to add a throws declaration to the method signature.

2. Get rid of your custom exception type and instead use Java's built-in NoSuchElementException, which already inherits from RuntimeException. This is almost certainly the better option.