handout #6
CSE143—Computer Programming II
Programming Assignment #2
due: Thursday, 6/30/05, 9 pm
(courtesy of Stuart Reges)
In this programming assignment we will continue
to practice using arrays and classes.
You are to implement a class called LetterInventory
that can be used to keep track of an inventory of letters of the alphabet. The constructor for the class takes a String
and computes how many of each letter are in the String. This is the information the object keeps
track of (how many a’s, how many b’s,
etc). It ignores the case of the letters
and ignores anything that is not an alphabetic character (e.g., it ignores
punctuation characters, digits and anything else that is not a letter).
Your
class should have the following public methods.
Method |
Description |
LetterInventory(String data) |
Constructs
an inventory (a count) of the alphabetic letters in the given string,
ignoring the case of letters and ignoring any non-alphabetic characters |
int get(char letter) |
Returns
a count of how many of this letter are in the inventory. Letter might be lowercase or uppercase
(your method shouldn’t care). If a nonalphabetic character is passed, your method should
throw an IndexOutOfBoundsException |
void
set(char letter, int value) |
Sets
the count for the given letter to the given value. Letter might be lowercase or
uppercase. If a nonalphabetic
character is passed, your method should throw an IndexOutOfBoundsException |
int size() |
Returns
the sum of all of the counts in this inventory. This operation should be “fast” in
that it should store the size rather
than having to compute it each time this method is called. |
boolean isEmpty() |
Returns
true if this inventory is empty (all counts are 0). This operation should be fast in that it
should not need to examine each of the 26 counts when it is called. |
String
toString() |
Returns
a String representation of the inventory with the letters all in lowercase
and in sorted order and surrounded by square brackets. The number of occurrences of each letter
should match its count in the inventory.
For example, an inventory of 4 a’s, 1 b, 1 l
and 1 m would be represented as “[aaaablm]”. |
LetterInventory add(LetterInventory other) |
Constructs
and returns a new LetterInventory object that represents the sum of this
letter inventory and the other given LetterInventory. The counts for each letter should be added
together. |
LetterInventory subtract(LetterInventory other) |
Constructs
and returns a new LetterInventory object that represents the result of
subtracting the other inventory from this inventory (i.e., subtracing the counts in the other inventory from this
object’s counts). If any resulting
count would be negative, your method should return null. |
You should implement this class with an array of
26 counters (one for each letter) along with any other data fields you find
that you need.
You will need to know certain things about the
properties of letters and type char. You
might want to look at the Character class for useful methods (e.g., there is a toLowerCase method).
You can compare different values of type char using less-than and
greater-than tests. All of the lowercase
letters appear grouped together in type char (‘a’ is followed by ‘b’ followed
by ‘c’, and so on) and all of the uppercase letters appear grouped together in
type char (‘A’ followed by ‘B’ followed by ‘C’ and so on). Because of this, you can compute a letter’s
displacement (or distance) from the letter “a” with an expression like the
following (this expression assumes the letter is a lowercase letter):
letter
- 'a'
You should write your own testing program to
make sure that your class works properly, but you will not have to turn in your
testing program.
In terms of correctness, your class must provide
all of the functionality described above and your size and isEmpty
methods must be fast, as described. In
terms of style, we will be grading on your use of comments, good variable
names, consistent indentation and good coding style to implement these
operations.
You MUST
name your file LetterInventory.java and turn it in
electronically from the “assignments” link on the class web page.