Java

Write an intersection method for the ResizableArrayBag class.

The intersection of two bags is the overlapping content of the bags. Intersections are explained in more detail in Chapter 1, #6.

An intersecion might contain duplicates.

The method should not alter either bag. The current bag and the bag sent in as a parameter should be the same when the method ends.

The method header is:

public BagInterface intersection(ResizableArrayBag anotherBag)

Example:

bag1 contains (1, 2, 2, 3)

bag2 contains (2, 2, 2, 4, 5)

then bag1.intersection(bag2) would return a new bag that contains (2, 2)

The contents of bag1 and bag2 would be the same.

(The order of the intersection bag might not match the above, since bags are unordered.)

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import java.util.Arrays;

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 < numberOfEntries; 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 < numberOfEntries; 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 < numberOfEntries)) {

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 <= givenIndex < numberOfEntries.

// 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