3) An Iterator (that is an object that has the methods in the Iterator interface

Question

3) An Iterator (that is an object that has the methods in the Iterator interface) allows access to each data element in a collection. How is that different from simply concatenating the values of the fields of all the data elements into a long string using the toString( ) method for a collection such as an OrderedList or UnorderedList?


public class ArrayIterator<T> implements Iterator<T> {       private T arrayOfData; //this will hold the data from the collection to iterate over       private int currentCusrsor; //this will hold the subscript of the next item to access

     public ArrayIterator(T [ ] array, int numberOfElements)      {          //create an array to hold a copy of the collection to iterate over           arrayOfData = (T[ ]) (new Object[numberOfElements]);           for(int k = 0; k < arrayOfData.length; k++)           {                    arrayOfData[k] = array[k];           }          currentCursor = 0;    }

   public T next( )   {          //if there is not another data item that has not been accessed yet         //throw an exeption. I just made up this exception class       if(!hasNext( ))                throw new NothingLeftToIterateOverException(“In ArrayIterator”);

      currentCursor ++;       return [arrayOfData [currentCursor - 1]; }

pubic boolean hasNext( ) {     //this method is supposed to return true if there are any data items    //in the array that have not yet been accessed. You are to write the    //one line of code to do this

}

public void remove( ) throws UnsupportedOperationExeption {     //Because we are never going to use this method we will     //simply create and throw and exception whenever this    //method is called. This is not a Java built-in Exception class,   //it is one the authors of the textbook created.   throw new UnsupportedOperationException(“The remove operation for this iterator is not “ +                                                                                         supported”); } }//end of ArrayIterator class definition

6) Now write the class definition for the NothingLeftToIteratorOver exception used above.

Explanation / Answer

/**
*
* @author Sam
*/
public class ArrayIterator<T> implements Iterator<T> {     
    private T[] arrayOfData; //this will hold the data from the collection to iterate over     
    private int currentCursor; //this will hold the subscript of the next item to access
    public ArrayIterator(T [ ] array, int numberOfElements)      {          //create an array to hold a copy of the collection to iterate over         
        arrayOfData = (T[ ]) (new Object[numberOfElements]);         
        for(int k = 0; k < arrayOfData.length; k++) {                  
            arrayOfData[k] = array[k];
        }    
    currentCursor = 0;
    }
      

    @Override
   public T next()   {        
       //if there is not another data item that has not been accessed yet
       //throw an exeption. I just made up this exception class
       if(!hasNext( ))
           throw new NothingLeftToIterateOverException("In ArrayIterator");
      currentCursor ++;     
      return arrayOfData [currentCursor - 1];
   }

    @Override
public boolean hasNext( ) {
     //this method is supposed to return true if there are any data items
     //in the array that have not yet been accessed. You are to write the
     //one line of code to do this
     return currentCursor != arrayOfData.length;
}

    @Override
    public void remove( ) throws UnsupportedOperationException {
    //Because we are never going to use this method we will
    //simply create and throw and exception whenever this
    //method is called. This is not a Java built-in Exception class,
    //it is one the authors of the textbook created.
    throw new UnsupportedOperationException("The remove operation for this iterator is not " +
            "supported");
}
}//end of ArrayIterator class definition

class NothingLeftToIterateOverException extends RuntimeException{

    public NothingLeftToIterateOverException(String message) {
        super(message);
    }
  
}

Here you go champ... Like it?

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