Question

Array with Iterator. Java style

Implement an array data structure as a class JstyArray<E> to support the Iterable interface such that the following code works:

JstyArray<Integer> data;

data = new JstyArray<Integer>(10);

for (int i = 0; i < 10; ++i) {
    data.set(i, new Integer(i) );
}

int sum = 0;
for ( int v : data ) {
    if (v == null)
        continue; // empty cell
    sum += v;
}

The iterator provided by this class follows the behaviour of typical Java style (Jsty). If the underlying collection is modified, the iterator becomes invalid and an exception is raised.

An example of code that may generate an exception is below:

try {
    int sum = 0;
    for ( int v : data ) {
        if (v == null) continue;
        if (v < 7)
            data.remove(0); // remove the first element
        // continue looping
        sum += v;
    }
} catch (NoSuchElementException nsee) {
    // ... handle as needed
}

There are 4 necessary methods for the Array. get(), set(), remove() and iterator().

There are 2 necessary methods for Iterator. hasNext() and next().

Other than these, you need to create more methods for communicating between Array and the Iterator. Object references are very useful in this scenario.

Once you have an iterator going. There is the next step of handling multiple iterators for the same data structure. More than one iterator can exist, at different times. There are iterators which are

•are invalid and have raised an exception, or

•are invalid and have not yet raised an exception, or

•are valid, they were created after modification to the data structure.

Multiple iterators are one of the harder tests

THERE ARE TWO CLASSES USED as shown below:

....................................................................................................................

JstyIterator.java:

/*
* An iterator for the class JstyArray. Performs all standard tasks of an iterator.
* Specifically, when calling next() on an invalid iterator, a NoSuchElementException is raised by this class.
*
*/
import java.util.Iterator;
import java.util.NoSuchElementException;

public class JstyIterator implements Iterator{

private JstyArray array;

private int index;

public JstyIterator(JstyArray array) {

this.array = array;

index = 0;

}

// YOUR CODE ANYWHERE IN THIS CLASS

public boolean hasNext() {

// YOUR CODE ANYWHERE IN THIS CLASS

if (array.size == index)

return false;

else
return true;

}

public E next() throws NoSuchElementException {

// YOUR CODE ANYWHERE IN THIS CLASS

if (array.list.size() != array.size)

throw new NoSuchElementException("Array elements have been modified !");

else if (hasNext()) {

return array.get(index++);

} else {

throw new NoSuchElementException("There are no elements in the array. Size = " + array.size);

}

}

public void remove() {

// we need this method for the nagging Java compiler

// you may leave empty

}

}

..........................................................................................................................................................

JstyArray.java:

/*
* An array that implements the Iterable interface.
* Returns an iterator that would raise an exception if the array was modified (set or remove)
*
*/

import java.util.LinkedList;

public class JstyArray implements Iterable{

// YOUR CODE ANYWHERE IN THIS CLASS

private E[] array;

public static final int CAPACITY = 100;

public int size;

public int capacity;

public LinkedList list;

// there could be more instance variables!

/*
* initialise array with capacity. If capacity is less than 1, use CAPACITY.
*
*/

@SuppressWarnings("unchecked")

public JstyArray(int capacity) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (capacity
{

array = (E[]) new Object[CAPACITY];

this.capacity = CAPACITY;

list = new LinkedList();

size = 0;

}

else

{

array = (E[]) new Object[capacity];

this.capacity = capacity;

list = new LinkedList();

size = 0;

}

}

/*
* if index is outside range of array. simply return
*
*/

public void set(int i, E val) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return;

else

{

array[i] = val;

list.add(i, val);

size++;

}

}

/*
* if index is outside range of array. return null
*
*/

public E get(int i) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return null;

else

return array[i];

}

/*
* if index is outside range of array. return null
*
*/

public E remove(int i) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return null;

else

{

list.remove(i);

E e = array[i];

array[i] = null;

return e;

}

}

public JstyIterator iterator() {

// YOUR CODE ANYWHERE IN THIS CLASS

return new JstyIterator(this);

}

}

.........................................................................................................................................................................

It passes some testcase but not all.

TESTCASES testremove Begin4 V testPrintEachNoException testremoveEnd5 V testNested1 testremoveEnd3 V testremove Begin3 X testConsecutiveUseBadGood X testremoveEnd1 X testremoveEnd2 X testremoveEnd4 X testremoveBegin2 X testremove Single X testConsecutiveUseGoodBadGood

Can you fix my code for it to pass all testcases

Answer 1

PROGRAM CODE:

JstyArray.java

package array2;

/*

* An array that implements the Iterable interface.

* Returns an iterator that would raise an exception if the array was modified (set or remove)

*

*/

import java.util.LinkedList;

import java.util.NoSuchElementException;

public class JstyArray<E> implements Iterable<E>{

// YOUR CODE ANYWHERE IN THIS CLASS

private E[] array;

public static final int CAPACITY = 100;

public int size;

public int capacity;

public LinkedList<E> list;

// there could be more instance variables!

/*

* initialise array with capacity. If capacity is less than 1, use CAPACITY.

*

*/

@SuppressWarnings("unchecked")

public JstyArray(int capacity) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (capacity<1)

{

array = (E[]) new Object[CAPACITY];

this.capacity = CAPACITY;

list = new LinkedList<E>();

size = 0;

}

else

{

array = (E[]) new Object[capacity];

this.capacity = capacity;

list = new LinkedList<E>();

size = 0;

}

}

/*

* if index is outside range of array. simply return

*

*/

public void set(int i, E val) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return;

else

{

array[i] = val;

list.add(i, val);

size++;

}

}

/*

* if index is outside range of array. return null

*

*/

public E get(int i) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return null;

else

return array[i];

}

/*

* if index is outside range of array. return null

*

*/

public E remove(int i) {

// YOUR CODE ANYWHERE IN THIS CLASS

if (i >= capacity)

return null;

else if(array[i] == null)

{

   throw new NoSuchElementException("No such element !");

}

else

{

list.remove(i);

E e = array[i];

array[i] = null;

//size--;

return e;

}

}

public JstyIterator<E> iterator() {

// YOUR CODE ANYWHERE IN THIS CLASS

return new JstyIterator<E>(this);

}

}

JstyIterator.java

package array2;

/*

* An iterator for the class JstyArray. Performs all standard tasks of an iterator.

* Specifically, when calling next() on an invalid iterator, a NoSuchElementException is raised by this class.

*

*/

import java.util.Iterator;

import java.util.NoSuchElementException;

public class JstyIterator<E> implements Iterator<E>{

private JstyArray<E> array;

private int index;

private int initialSize;

public JstyIterator(JstyArray<E> array) {

this.array = array;

this.index = 0;

this.initialSize = array.list.size();

}

// YOUR CODE ANYWHERE IN THIS CLASS

public boolean hasNext() {

// YOUR CODE ANYWHERE IN THIS CLASS

if (array.size == index)

return false;

else

return true;

}

public E next() throws NoSuchElementException {

// YOUR CODE ANYWHERE IN THIS CLASS

if (initialSize != array.list.size())

throw new NoSuchElementException("Array elements have been modified !");

else if (hasNext()) {

return array.get(index++);

} else {

throw new NoSuchElementException("There are no elements in the array. Size = " + array.size);

}

}

public void remove() {

// we need this method for the nagging Java compiler

// you may leave empty

}

}

JstTester.java

package array2;

import java.util.NoSuchElementException;

public class JstTester {

   static JstyArray<Integer> array;

  

   public static void main(String[] args) {

       array = new JstyArray<>(10);

       for(int i=0; i<10; i++)

           array.set(i, i);

       //Test case - testRemoveBegin4

       array.remove(4);

       //Test case - testPrintEachNoException

       System.out.println("\nTest case - testPrintEachNoException");

       JstyIterator<Integer> itr = array.iterator();

       while(itr.hasNext())

       {

           System.out.print(itr.next() + " ");

       }

       System.out.println("");

       //Test case - testRemoveBegin4

       array.remove(5);

      

      

      

       System.out.println("\nTest case - testConsecutiveBad");

       itr = array.iterator();

       array.remove(1);

       try{

           while(itr.hasNext())

       {

           System.out.print(itr.next() + " ");

       }}catch (NoSuchElementException e) {

           System.out.println("Exception: Error: " + e.getMessage());

       }

      

       itr = array.iterator();

       System.out.println("\nTest case - testConsecutiveGood");

       while(itr.hasNext())

       {

           System.out.print(itr.next() + " ");

       }

       System.out.println("");

      

       try

       {

       array.remove(5);

       }catch (Exception e) {

           System.out.println("\nException: Error: " + e.getMessage());

       }

   }

}

OUTPUT:

Test case - testPrintEachNoException

0 1 2 3 null 5 6 7 8 9

Test case - testConsecutiveBad

Exception: Error: Array elements have been modified !

Test case - testConsecutiveGood

0 null 2 3 null null 6 7 8 9

Exception: Error: No such element !