(solution) toString method for this please (Java Program) I have this right

(solution) toString method for this please (Java Program) I have this right

toString method for this please (Java Program)

I have this right now

public String toString() {
String output = “[“;
for(int i =0;i

return output += “]”;

CSE 143: Computer Programming II Autumn 2016 HW1: Letter Inventory (due Thursday, October 6, 2016 at 11:30pm)
This assignment focuses on arrays and classes. Turn in the following files using the link on the
course website:
? LetterInventory.java ? A class that keeps track of an inventory of letters of the alphabet.
? decodedCryptogram.txt ? The decoded version of the cryptogram, cryptogram.txt, which you will
be able to create using your program. (See later pages.)
You will need the support files FrequencyAnalysis.java and cryptogram.txt from the resources button
on the course website to finish decrypting the cryptogram; place these in the same folder as your program
or project. If you are using EZclipse, the files will be automatically downloaded for you. The code you
submit must work properly with unmodified versions of the supporting files. Implementation Details
Your LetterInventory class should. . .
? Store the inventory (how many a?s, how many b?s, etc.) as an array with 26 counters (one for each
letter) along with any other data fields you find that you need
? Ignore the case of the letters (e.g., ?a? and ?A?)
? Ignore non-alphabetic characters (e.g., digits, punctuation, etc.) 
Not an ArrayList!  ? Introduce a class constant for the value 26 to make the class more readable
? Should NOT have any extra public methods or have any extra behavior beyond what this spec describes ?26? should only
appear once. Constructors
The LetterInventory class should have the following two constructors:
public LetterInventory()  Constructs an empty inventory (all counts are 0).
public LetterInventory(String data) Constructs an inventory (a count) of the alphabetic letters in data (the given string). Uppercase and
lowercase letters should be treated as the same. All non-alphabetic characters should be ignored. Be careful to
remove redundancy between
the constructors. Methods
The LetterInventory class should have the following public methods:
public int get(char letter) Returns the number of times the given letter appears in this inventory. Letter can be lowercase or
uppercase (your method shouldn?t care). If a non-alphabetic character is passed, your method should
throw an IllegalArgumentException.
public 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 non-alphabetic character is passed or if value is negative, your method should throw an
Don?t forget to
comment your
exceptions! public int size() Returns the sum of all of the counts in this inventory. This operation should be ?fast? in the sense
that it should store the size rather than computing it each time the method is called.
public boolean isEmpty() Returns true if this inventory is empty (all counts are 0). This operation should be ?fast? in the sense
that it shouldn?t loop over the array each time the method is called. 
Avoid recomputation
by saving the
value(s). public String toString() Returns a String representation of the inventory with all the letters in lowercase, 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 `, and 1 m would be represented as
public LetterInventory add(LetterInventory other) Constructs and returns a new LetterInventory object that represents the sum of this
LetterInventory and the other given LetterInventory. The counts for each letter should be
added together. The two LetterInventory objects being added together (this and other) should
not be changed by this method. You might be tempted to implement the add method by calling the
toString method, but you may not use that approach, because it would be inefficient for inventories
with large character counts.
Below is an example of how the add method might be called:
1 LetterInventory inventory1 = new LetterInventory("George W. Bush");
2 LetterInventory inventory2 = new LetterInventory("Hillary Clinton");
3 LetterInventory sum = inventory1.add(inventory2); The first inventory would correspond to [beegghorsuw], the second would correspond to
[achiilllnnorty] and the third would correspond to [abceegghhiilllnnoorrstuwy].
public LetterInventory subtract(LetterInventory other) Constructs and returns a new LetterInventory object that represents the difference of this letter
inventory and the other given LetterInventory. The counts from the other inventory should be
subtracted from the counts of this one. The two LetterInventory objects being subtracted (this
and other) should not be changed by this method. If any resulting count would be negative, your
method should return null.
public double getLetterPercentage(char letter) Returns a double from 0.0 to 1.0 representing the percentage of letters in the inventory that are
the given letter. If there are no letters in the inventory, this method should always return 0. If a
non-alphabetic character is passed, your method should throw an IllegalArgumentException. Useful Properties of Strings and Characters
You will need to know certain things about the properties of letters and type char. It might help to look
at the section in Chapter 4 of the textbook about this topic.
One of the most important ideas is that the values of type char have corresponding integer values. There 2 
add and subtract should
not change the
existing Letter
They should
create new ones
Don?t forget the
special case for
this method! is a character with value 0, a character with value 1, a character with value 2 and so on. You can compare
different values of type char using less-than and greater-than tests. For example:
1 if (ch >= 'a') {

3 } 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 variable letter is of type
char and stores a lowercase letter):
letter – 'a' 
Use this to find
indices and
offsets. Going in the other direction, if you know a char?s integer equivalent, you can cast the result to char to
get the character. For example, suppose that you want to get the letter that is 8 away from ?a?. You could
char result = (char) ('a' + 8);
This assigns the variable result the value ?i?.
As in these examples, you should write your code for LetterInventory in terms of displacement from a
fixed letter like ?a? rather than including the specific integer value of a character.
You probably want to look at the String and Character classes for useful methods (e.g., there is a
toLowerCase method in each). You will have to pay attention to whether a method is static or not.
The String methods are mostly instance methods, because Strings are objects. The Character methods
are all static, because char is a primitive type. For example, assuming you have a variable called s that
is a String, you can turn it into lowercase by saying:
s = s.toLowerCase();
This is a call on an instance method where you put the name of the object first. But chars are not
objects and the toLowerCase method in the Character class is a static method. So, assuming you have
a variable called ch that is of type char, you?d turn it to lowercase by saying:
ch = Character.toLowerCase(ch);
You can read about String operations on pages 160?166 of the textbook. 
Use ?a?, not
?97? in your
code. Translating the Ciphertext
In this assignment, you?ve implemented the LetterInventory data structure. In particular, you?ve seen
the data structure from the implementor?s view. One possible client for this data structure is a class
that performs frequency analysis of letters in a cryptogram to decode it. One type of cryptogram which
frequency analysis of letters is often very useful for is substitution ciphers. A substitution cipher is a type
of cryptogram where all occurrences of each particular letter are all replaced with a single other letter.
For instance, if the original text were ?hello i like bananas?, one possible substitution cipher would make
the following replacements:
Then, the encrypted text would be:
xtppr q pqot avuvuvw.
We have given you a client implementation of a FrequencyAnalysis program which uses your LetterInventory.
When your LetterInventory is working, you should be able to run the FrequencyAnalysis on ciphertext.txt
to decode it. Turn in the result as decodedCryptogram.txt Development Strategy
The best way to write code is in stages. If you attempt to write everything at once, it will be significantly
more difficult to debug, because any bugs are likely not isolated to a single place.
For this assignment we will provide you with a development strategy and some testing code. The tests we
provided are not exhaustive; they are meant as an example of what kind of tests we expect you to write.
3 We suggest that you develop the program in the follow four stages:
(1) In this stage, we want to test constructing a LetterInventory and examining its contents. So, the
methods we will implement are the constructors, the size method, the isEmpty method, the get
method, and the toString method. Even within this stage you can develop the methods slowly.
You should implement these methods in the order above. The testing program will test them in
this order; so, it will be possible to implement them one at a time.
(2) In this stage, we want to add the set method which allows the client to change the number of
occurrences of an individual letter. The testing program will verify that other methods work properly
in conjunction with set (the get, isEmpty, size, and toString methods).
(3) In this stage, we want to include the add and subtract methods. You should write the add method
first and make sure it works. The testing program first tests add; so, don?t worry that the fact that
the tests on subtract fail initially.
(4) Finally, we want to include the getLetterPercentage method. A reasonable test of this step is to
run the FrequencyAnalysis and check that the text makes sense.
We have provided some testing code for the first three stages (but not the fourth). You may discuss how
to write testing code with other students. Keep in mind that the tests are not guaranteed to be exhaustive.
They are meant to be examples of the kinds of tests you should perform. Style Guidelines and Grading
Unless otherwise specified, your solution should use only material covered so far. Avoid Redundancy
Create ?helper? method(s) to capture repeated code. As long as all extra methods you create are
private (so outside code cannot call them), you can (and should) have additional methods in your
LetterInventory class beyond those specified here. If you find that multiple methods in your class do
similar things, you should create helper method(s) to capture the common code. No Extra Data Structures
Your letter inventory should maintain its list of letters internally in a field of type array as specified here.
Do not create any extra data structures. Data Fields
Properly encapsulate your objects by making data your fields private. Avoid unnecessary fields; use fields
to store important data of your objects but not to store temporary values only used in one place. Fields
should always be initialized inside a constructor or method, never at declaration. Java Style Guidelines
Appropriately use control structures like loops and if/else statements. Avoid redundancy using techniques
such as methods, loops, and factoring common code out of if/else statements. Properly use indentation,
good variable names, and types. Do not have any lines of code longer than 80 characters. Commenting
You should comment your code with a heading at the top of your class with your name, section, and a
description of the overall program. All method headers should be commented as well as all complex sections
of code. Comments should explain each method?s behavior, parameters, return values, and assumptions
made by your code, as appropriate. The ArrayIntList class from lecture provides a good example of
the kind of documentation we expect you to include. You do not have to use the pre/post format, but
you must include the equivalent information?including the exact name of the exception thrown if a
precondition is violated.
Do not add
extra public