structure
Class ArrayIterator

java.lang.Object
  |
  +--structure.AbstractIterator
        |
        +--structure.ArrayIterator

All Implemented Interfaces:

Enumeration, Iterator

public class ArrayIterator

extends AbstractIterator

A conveniece class that provies a mechanism to iterate over arrays that is analogous to the iteration techniques employed by the structures in this package.

Example Usage:

To prove that loops are faster than iteration we could use the following:

 public static void main(String[] argv){
	//a randomly generated test string
	String testString = "For loops are much faster than iterators";

	//an array over which to iterate
	String[] test = new String[10000000];
	
	//longs to calculate lenght of computation
	long start, finish, iteration, looping;

	//populate test array with our test string
	for(int i=0; i<test.length; i++) test[i] = testString;
	
	//compute test for iteration
	start = System.currentTimeMillis();
	for(Iterator i = new ArrayIterator(test); i.hasNext();i.next()){}
	finish = System.currentTimeMillis();
	iteration = finish - start;
	System.out.println("Iteration over array took " + iteration + 
			   " milliseconds to perform.");

	//compute test for looping
	start = System.currentTimeMillis();
	for(int i=0; i<test.length; i++){}
	finish = System.currentTimeMillis();
	looping = finish - start;
	System.out.println("Looping over array took " + (finish-start) + 
			   " milliseconds to perform.");
	
	System.out.println("Iterators are " + (iteration/(double)looping) + " times " +
			   "slower than loops.");
 }
 

Field Summary

protected int	count The number of elements in the array over which to iterate
protected int	current The current item in the iteration
protected Object[]	data The array over which this iterator iterates
protected int	head The index of the first item in the iteration
protected int	remaining The number of items remaining in the itearation

Constructor Summary

ArrayIterator(Object[] source)
Construct an iterator that iterates over the entire contents of an array.

ArrayIterator(Object[] source, int first, int size)
Constructs an iterator that will iterate over a specified portion of the source array.

Method Summary

Object	get() Return the object currently specified by the iteration without advancing the iterator to the next object.
boolean	hasNext() Returns true iff there are elements specified by our iterator that have not been visited by the current iteration.
static void	main(String[] argv) test code to prove that iterators are slower than for loops
Object	next() Return the next object in our iteration and advance the iterator to the next object in the iteration.
void	reset() Return the iteration to the original state specified by the constructor.

Methods inherited from class structure.AbstractIterator

hasMoreElements, nextElement, remove, value

Methods inherited from class java.lang.Object

, clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, toString, wait, wait, wait

Field Detail

data

protected Object[] data

The array over which this iterator iterates

head

protected int head

The index of the first item in the iteration

count

protected int count

The number of elements in the array over which to iterate

current

protected int current

The current item in the iteration

remaining

protected int remaining

The number of items remaining in the itearation

Constructor Detail

ArrayIterator

public ArrayIterator(Object[] source)

Construct an iterator that iterates over the entire contents of an array.

Parameters:

source - The array over which to iterate.

ArrayIterator

public ArrayIterator(Object[] source,
                     int first,
                     int size)

Constructs an iterator that will iterate over a specified portion of the source array.

Parameters:

source - The array over which to iterate.

first - The index at which we will start our iteration.

size - The number of elements following that start index that are to be iterated over.

Method Detail

reset

public void reset()

Return the iteration to the original state specified by the constructor.

Overrides:

reset in class AbstractIterator

Postcondition:

The iteration is returned to its original state.

hasNext

public boolean hasNext()

Returns true iff there are elements specified by our iterator that have not been visited by the current iteration.

Overrides:

hasNext in class AbstractIterator

Returns:

True iff there are elements specified by our iterator that have not been visited by the current iteration.

next

public Object next()

Return the next object in our iteration and advance the iterator to the next object in the iteration.

Overrides:

next in class AbstractIterator

Returns:

The next object in our iteration.

get

public Object get()

Return the object currently specified by the iteration without advancing the iterator to the next object.

Overrides:

get in class AbstractIterator

Returns:

The next object in our iteration.

main

public static void main(String[] argv)

test code to prove that iterators are slower than for loops