Converting an Enumeration to Iterator

Question

I have a problem on a worksheet which is to create an adapter to convert an Enumeration to an Iterator. When I try to run the following code I get a null pointer exception.

import java.util.Vector;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Iterator;

public class ConvertEnumeration {

    public static void main(String [] args) {

        int [] ourArray = {0,1,2,3,4,5,6,7,8,9};
        Vector vector = new Vector(Arrays.asList(ourArray));

        //Get Enumerator 
        Enumeration enumerator = vector.elements();

        EnumerationToIterator enumToIt = new EnumerationToIterator(enumerator);
        while(enumToIt.hasNext()) {
            System.out.println(enumToIt.next());
        }
    }

}


//Convert our enumeration to Iterator!
class EnumerationToIterator implements Iterator {

    //Our enumeration
    Enumeration enmueration;

    //Constructor
    public EnumerationToIterator(Enumeration enmueration){
        enmueration = this.enmueration;
    }

    //Our Methods
    public boolean hasNext(){
        return enmueration.hasMoreElements();
    }

    public Object next(){
        return enmueration.nextElement();
    }

    public void remove(){
        throw new UnsupportedOperationException();
    }

}

Another point to note is that I can not print out the int's from the Enumeration after I have created it in the first place.

Answer 1

Java 5 and Later

No need to reinvent the wheel. Just use Collections.list(Enumeration<T> e), which returns an ArrayList<T>. Then use ArrayList.iterator() to get an Iterator.

Java 9 and Later

Enumerations now have a method to convert directly to an iterator:

enumeration.asIterator();

Answer 2

Wrong assignment in your constructor. It needs to be this.enmueration = enmueration;
enmueration is the constructor argument, and this.enmueration is the object attribute.