student_classes

Class Bag<T>

java.lang.Object

student_classes.Bag<T>

Type Parameters:

T -

All Implemented Interfaces:

java.lang.Iterable<T>

public class Bag<T>
extends java.lang.Object
implements java.lang.Iterable<T>

A "bag" is a data-structure that implements a multiset, which is a set that allows multiple (duplicates). The standard operators on such a data-structure include:

• Bag() --creates an empty bag (optionally, perhaps a default size?)
• add( T ele ) --adds an element to the bag.
• remove( T ele ) --removes an element from the bag; may throw IllegalStateException --in the event that ele is NOT in the Bag.
• contains( T ele ) --returns True if ele is in bag.
• count( T ele ) --returns the number of occurrences of ele in set. This is called the "multiplicity" of the element.
• asSet() --returns a collection of the elements in this bag as set.
• size() --returns the number of elements in this bag taking into account their multiplicities. For example: if the Bag contains the following elements with multiplicities:

  Key Count

  ------------

  "A" 2

  "B" 3

  "C" 1

  size() => 6.

• iterator() --returns an Iterator that also takes into account the multiplicities of each key. So, an iterator() should iterate over exactly the same number of elements as size().

Author:

UMD CS Department.

Constructor Summary

Constructors

Constructor and Description
Bag() Default (sole) constructor.

Method Summary

Modifier and Type	Method and Description
void	add(T ele) Adds ele (T) to the bag.
java.util.Set<T>	asSet() Return the keys as a Set---i.e., no duplicates, order-unimportant.
boolean	contains(T ele) Returns true if this Bag contains at least one copy of the key.
int	count(T ele) Returns the number of occurrences of ele in the Bag; returns 0 in the event that ele is not in Bag.
java.util.Iterator<T>	iterator() Returns an object that iterates (implements the Iterator interface) over objects in the Bag.
void	remove(T ele) Effectively remove the ele from the bag.
int	size() The "size" of a bag is the cardinality of the multiset that it embodies.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

Bag

public Bag()

Default (sole) constructor. Sets up internal data structures.

Method Detail

add

public void add(T ele)

Adds ele (T) to the bag. If ele was already in the Bag, then its internal count is incremented by 1; otherwise a new entry is made, indicating that at least 1 ele exists in this Bag.

Parameters:

ele -

remove

public void remove(T ele)

Effectively remove the ele from the bag. Note, several possibilities here:

• If the ele isn't in the Bag, throw an Illegal State Exception.
• If only one ele exists in the Bag, then remove it.
• If more than one ele exists in the Bag, make whatever changes are necessary to indicate that one fewer ele now exists in the Bag. Note, how you do this will depend upon your internal data-structure.

Parameters:

ele -

contains

public boolean contains(T ele)

Returns true if this Bag contains at least one copy of the key.

Parameters:

ele -

Returns:

count

public int count(T ele)

Returns the number of occurrences of ele in the Bag; returns 0 in the event that ele is not in Bag. *

Parameters:

ele -

Returns:

asSet

public java.util.Set<T> asSet()

Return the keys as a Set---i.e., no duplicates, order-unimportant. Use this function to determine the number of unique entries in the Bag!

Returns:

size

public int size()

The "size" of a bag is the cardinality of the multiset that it embodies. In English, that means that the size of your bag must accumulate the multiplicities of each element. For example: suppose your Bag contains

Key Count

------------

"A" 2

"B" 3

"C" 1

Then its size is 6.

Returns:

iterator

public java.util.Iterator<T> iterator()

Returns an object that iterates (implements the Iterator interface) over objects in the Bag.

You will most like return an instance of an inner class that you design to manage an immutable Iteration of keys over this bag.

Specified by:

iterator in interface java.lang.Iterable<T>

Returns: