Computer Science 210
Data Structures

Fall 2017, Siena College

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Iterators BlueJ Project

Click here to download a BlueJ project for Iterators.

Iterators Source Code

The Java source code for Iterators is below. Click on a file name to download it.

Iterators.java

import structure5.*;
import java.util.Iterator;

/**
   Testing class for Iterator examples

   @author Jim Teresco, originally in 2009
*/

public class Iterators {

    public static final int SIZE = 10;

    public static void main(String args[]) {

	// create a vector of integers for testing
	Vector<Integer> v = new Vector<Integer>(SIZE);
	for (int i=0; i<SIZE; i++) {
	    v.add(i);
	}

	// traverse with the standard iterator
	System.out.println("Standard iterator:");
	Iterator<Integer> vi = v.iterator();
	while (vi.hasNext()) {
	    System.out.println(vi.next());
	}

	// traverse with even-only iterator
	System.out.println("Even-only iterator:");
	vi = new VectorEvenIterator<Integer>(v);
	while (vi.hasNext()) {
	    System.out.println(vi.next());
	}

	// traverse with prefix sum iterator
	System.out.println("Prefix sum iterator:");
	vi = new PrefixSumIterator(v);
	while (vi.hasNext()) {
	    System.out.println(vi.next());
	}

    }
}

PrefixSumIterator.java

import structure5.*;
/**
 * An iterator class for implementing an iterator over a Vector 
 * of numbers that returns the prefix sum of the numbers rather
 * than the numbers themselves.  That is, the sum of all values
 * up to and include the current.
 *
 * @author, Jim Teresco, 2009
 */
public class PrefixSumIterator extends AbstractIterator<Integer>
{
    /**
     * The associated vector
     */
    protected Vector<Integer> theVector;
    /**
     * The index of the current value.
     */
    protected int current;

    /**
       The prefix sum of the items encountered so far.
    */
    protected int prefixSum;

    /**
     * Construct a vector iterator to traverse vector v
     *
     * @post constructs an initialized iterator associated with v
     * 
     * @param v The underlying vector.
     */
    public PrefixSumIterator(Vector<Integer> v)
    {
        theVector = v;
        reset();
    }

    /**
     * Reset the vector iterator to the first value in the vector.
     *
     * @post the iterator is reset to the beginning of the traversal
     */
    public void reset()
    {
        current = 0;
	prefixSum = 0;
    }

    /**
     * Determine if some of the elements have yet to be considered.
     *
     * @post returns true if there is more structure to be traversed
     * 
     * @return True if more elements are to be considered.
     */
    public boolean hasNext()
    {
        return current < theVector.size();
    }

    /**
     * Fetch a reference to the current value.
     *
     * @pre traversal has more elements
     * @post returns the current value referenced by the iterator 
     * 
     * @return A reference to the current value being considered.
     */
    public Integer get()
    {
        return new Integer(prefixSum+theVector.get(current).intValue());
    }
    
    /**
     * Return current value, and increment iterator to next
     * value to be returned (the next even-numbered entry)
     *
     * @pre traversal has more elements
     * @post increments the iterated traversal
     * 
     * @return the prefix sum of the values up to the current
     */
    public Integer next()
    {
	prefixSum += theVector.get(current).intValue();
	current++;
        return new Integer(prefixSum);
    }
}

VectorEvenIterator.java

import structure5.*;
/**
 * An iterator class for implementing an iterator over a Vector that
 * returns only the elements at even-numbered indices.
 *
 * Based on VectorIterator from Duane Bailey's stucture package
 *
 * @author, Jim Teresco, 2009
 */
public class VectorEvenIterator<E> extends AbstractIterator<E>
{
    /**
     * The associated vector
     */
    protected Vector<E> theVector;
    /**
     * The index of the current value.
     */
    protected int current;

    /**
     * Construct a vector iterator to traverse vector v
     *
     * @post constructs an initialized iterator associated with v
     * 
     * @param v The underlying vector.
     */
    public VectorEvenIterator(Vector<E> v)
    {
        theVector = v;
        reset();
    }

    /**
     * Reset the vector iterator to the first value in the vector.
     *
     * @post the iterator is reset to the beginning of the traversal
     */
    public void reset()
    {
        current = 0;
    }

    /**
     * Determine if some of the elements have yet to be considered.
     *
     * @post returns true if there is more structure to be traversed
     * 
     * @return True if more elements are to be considered.
     */
    public boolean hasNext()
    {
        return current < theVector.size();
    }

    /**
     * Fetch a reference to the current value.
     *
     * @pre traversal has more elements
     * @post returns the current value referenced by the iterator 
     * 
     * @return A reference to the current value being considered.
     */
    public E get()
    {
        return theVector.get(current);
    }
    
    /**
     * Return current value, and increment iterator to next
     * value to be returned (the next even-numbered entry)
     *
     * @pre traversal has more elements
     * @post increments the iterated traversal by 2
     * 
     * @return A reference to the current value, before increment.
     */
    public E next()
    {
	E result = theVector.get(current);
	current+=2;
        return result;
    }
}