import java.util.Arrays;

/**

A class that implements a bag of objects by using an array.

The bag is never full.

@author Frank M. Carrano

@author Timothy M. Henry

@version 4.0

*/

public final class ResizableArrayBag implements BagInterface

{

private T[] bag; // Cannot be final due to doubling

private int numberOfEntries;

private boolean initialized = false;

private static final int DEFAULT_CAPACITY = 25; // Initial capacity of bag

private static final int MAX_CAPACITY = 10000;

/** Creates an empty bag whose initial capacity is 25. */

public ResizableArrayBag()

{

this(DEFAULT_CAPACITY);

} // end default constructor

/** Creates an empty bag having a given initial capacity.

@param initialCapacity The integer capacity desired. */

public ResizableArrayBag(int initialCapacity)

{

checkCapacity(initialCapacity);

// The cast is safe because the new array contains null entries

@SuppressWarnings("unchecked")

T[] tempBag = (T[])new Object[initialCapacity]; // Unchecked cast

bag = tempBag;

numberOfEntries = 0;

initialized = true;

} // end constructor

/** Creates a bag containing given entries.

@param contents An array of objects. */

public ResizableArrayBag(T[] contents)

{

checkCapacity(contents.length);

bag = Arrays.copyOf(contents, contents.length);

numberOfEntries = contents.length;

initialized = true;

} // end constructor

/** Adds a new entry to this bag.

@param newEntry The object to be added as a new entry.

@return True. */

public boolean add(T newEntry)

{

checkInitialization();

if (isArrayFull())

{

doubleCapacity();

} // end if

bag[numberOfEntries] = newEntry;

numberOfEntries++;

return true;

} // end add

/** Retrieves all entries that are in this bag.

@return A newly allocated array of all the entries in this bag. */

public T[] toArray()

{

checkInitialization();

// The cast is safe because the new array contains null entries.

@SuppressWarnings("unchecked")

T[] result = (T[])new Object[numberOfEntries]; // Unchecked cast

for (int index = 0; index

{

result[index] = bag[index];

} // end for

return result;

} // end toArray

/** Sees whether this bag is empty.

@return True if this bag is empty, or false if not. */

public boolean isEmpty()

{

return numberOfEntries == 0;

} // end isEmpty

/** Gets the current number of entries in this bag.

@return The integer number of entries currently in this bag. */

public int getCurrentSize()

{

return numberOfEntries;

} // end getCurrentSize

/** Counts the number of times a given entry appears in this bag.

@param anEntry The entry to be counted.

@return The number of times anEntry appears in this ba. */

public int getFrequencyOf(T anEntry)

{

checkInitialization();

int counter = 0;

for (int index = 0; index

{

if (anEntry.equals(bag[index]))

{

counter++;

} // end if

} // end for

return counter;

} // end getFrequencyOf

/** Tests whether this bag contains a given entry.

@param anEntry The entry to locate.

@return True if this bag contains anEntry, or false otherwise. */

public boolean contains(T anEntry)

{

checkInitialization();

return getIndexOf(anEntry) > -1; // or >= 0

} // end contains

/** Removes all entries from this bag. */

public void clear()

{

while (!isEmpty())

remove();

} // end clear

/** Removes one unspecified entry from this bag, if possible.

@return Either the removed entry, if the removal

was successful, or null. */

public T remove()

{

checkInitialization();

T result = removeEntry(numberOfEntries - 1);

return result;

} // end remove

/** Removes one occurrence of a given entry from this bag.

@param anEntry The entry to be removed.

@return True if the removal was successful, or false if not. */

public boolean remove(T anEntry)

{

checkInitialization();

int index = getIndexOf(anEntry);

T result = removeEntry(index);

return anEntry.equals(result);

} // end remove

// Locates a given entry within the array bag.

// Returns the index of the entry, if located,

// or -1 otherwise.

// Precondition: checkInitialization has been called.

private int getIndexOf(T anEntry)

{

int where = -1;

boolean found = false;

int index = 0;

while (!found && (index

{

if (anEntry.equals(bag[index]))

{

found = true;

where = index;

} // end if

index++;

} // end while

// Assertion: If where > -1, anEntry is in the array bag, and it

// equals bag[where]; otherwise, anEntry is not in the array.

return where;

} // end getIndexOf

// Removes and returns the entry at a given index within the array.

// If no such entry exists, returns null.

// Precondition: 0

// Precondition: checkInitialization has been called.

private T removeEntry(int givenIndex)

{

T result = null;

if (!isEmpty() && (givenIndex >= 0))

{

result = bag[givenIndex]; // Entry to remove

int lastIndex = numberOfEntries - 1;

bag[givenIndex] = bag[lastIndex]; // Replace entry to remove with last entry

bag[lastIndex] = null; // Remove reference to last entry

numberOfEntries--;

} // end if

return result;

} // end removeEntry

// Returns true if the array bag is full, or false if not.

private boolean isArrayFull()

{

return numberOfEntries >= bag.length;

} // end isArrayFull

// Doubles the size of the array bag.

// Precondition: checkInitialization has been called.

private void doubleCapacity()

{

int newLength = 2 * bag.length;

checkCapacity(newLength);

bag = Arrays.copyOf(bag, newLength);

} // end doubleCapacity

// Throws an exception if the client requests a capacity that is too large.

private void checkCapacity(int capacity)

{

if (capacity > MAX_CAPACITY)

throw new IllegalStateException("Attempt to create a bag whose capacity exceeds " +

"allowed maximum of " + MAX_CAPACITY);

} // end checkCapacity

// Throws an exception if receiving object is not initialized.

private void checkInitialization()

{

if (!initialized)

throw new SecurityException ("Uninitialized object used " +

"to call an ArrayBag method.");

} // end checkInitialization

} // end ResizableArrayBag

Open Resizable ArrayBag and rename as ArraySet.java Re-write 'add' methods to prevent the addition of duplicate entries, using We can remove getFrequencyOf' method. - Global replace of 'Bag' with Set' either the contains' method or getIndexOf Update the test class - replace the 'testGetFrequencyOf method and add a method to verify that duplicates can't be added