For this week's lab, you will use two of the classes in the Java
Collection Framework: HashSet and TreeSet. You
will use these classes to implement a spell checker.
Set Methods
For this lab, you will need to use some of the methods that are
defined in the Set interface. Recall that if set is a Set, then the
following methods are defined:
You will also need to be able to traverse a set, using either an
iterator or a for-each loop.
Reading a Dictionary
The file words.txt (in the code directory) contains a list of
English words, with one word on each line. You will look up words
in this list to check whether they are correctly spelled. To make
the list easy to use, you can store the words in a set. Since there
is no need to have the words stored in order, you can use a
HashSet for maximum efficiency.
Use a Scanner to read the file. You can create a scanner,
filein, for reading from a file with a statement such
as:
filein = new Scanner
(new File("/classes/s09/cs225/words.txt"));
and that a file can be processed, token by token, in a loop such
as:
while (filein.hasNext()) {
String tk = filein.next();
process(tk); // do something with
the token
}
(For the wordlist file, a token is simply a word.)
Start your main program by reading the words from words.txt and
storing them in a HashSet<String>. For the purposes
of this program, convert all words to lower case
before putting them in the set. To make sure that you've read all
the words, check the size of the set. (It should be 72875.) You
could also use the contains method to check for the presence of
some common word in the set.
Checking the Words in a File
Once you have the list of words in a set, it's easy to read the
words from a file and check whether each word is in the set. Start
by letting the user select a file. You can either let the user type
the name of the file or you can use the following method:
/**
* Lets the
user select an input file using a standard file
* selection
dialog box. If the user cancels the dialog
* without
selecting a file, the return value is null.
*/
static File
getInputFileNameFromUser() {
JFileChooser fileDialog = new JFileChooser();
fileDialog.setDialogTitle("Select File for Input");
int option = fileDialog.showOpenDialog(null);
if (option != JFileChooser.APPROVE_OPTION)
return null;
else
return fileDialog.getSelectedFile();
}
Use a Scanner to read the words from the selected file. In order to
skip over any non-letter characters in the file, you can use the
following command just after creating the scanner (where in is the
variable name for the scanner):
in.useDelimiter("[^a-zA-Z]+");
(In this statement, "[^a-zA-Z]+" is a regular expression that
matches any sequence of one or more non-letter characters. This
essentially makes the scanner treat any non-letter the way it would
ordinarily treat a space.)
You can then go through the file, read each word (converting it to
lower case) and check whether the set contains the word. At this
point, just print out any word that you find that is not in the
dictionary.
Providing a List of Possible Correct Spellings
A spell checker shouldn't just tell you what words are
misspelled -- it should also give you a list of possible correct
spellings for that word. Write a method
static TreeSet corrections(String badWord, HashSet
dictionary)
that creates and returns a TreeSet<String>
containing variations on badWord that are contained in the
dictionary. In your main program, when you find a word that is not
in the set of legal words, pass that word to this method (along
with the set). Take the return value and output any words that it
contains; these are the suggested correct spellings of the
misspelled word. Here, for example, is part of the output from a
sample program when it was run with the HTML source of this page as
input:
html: (no suggestions)
cpsc: (no suggestions)
hashset: hash set
treeset: tree set
cvs: cs, vs
isempty: is empty
href: ref
txt: tat, tet, text, tit, tot, tut
filein: file in
pre: are, ere, ire, ore, pare, pee, per, pie, poe, pore, prep,
pres,
prey, pro, pry, pure, pyre,
re
hasnext: has next
wordlist: word list
getinputfilenamefromuser: (no suggestions)
jfilechooser: (no suggestions)
filedialog: file dialog
setdialogtitle: (no suggestions)
int: ant, dint, hint, in, ina, inc, ind, ink, inn, ins, inti,
into,
it, lint, mint, nit, pint,
tint
Note that the program was written so that it will not output the
same misspelled word more than once. (This is done by keeping a set
of misspelled words that have been output.) If the
corrections() method returns an empty set, the program
outputs the message "(no suggestions)". Since the corrections are
stored in a tree set, they are automatically printed out in
alphabetical order with no repeats.
The possible corrections that the program considers are as
follows:
• Delete any one of the letters from the misspelled word.
• Change any letter in the misspelled word to any other
letter.
• Insert any letter at any point in the misspelled word.
• Swap any two neighboring characters in the misspelled word.
• Insert a space at any point in the misspelled word (and check
that both of the words that are produced are in the
dictionary)
For constructing the possible corrections, you will have to make
extensive use of substrings. If w is a string, then
w.substring(0,i) is the string consisting of the first i
characters in w (not including the character in position i, which
would be character number i+1). And
w.substring(i) consists of the characters of w from
position i through the end of the string. For example, if
ch is a character, then you can change the i-th
character of w to ch with the statement:
String s = w.substring(0,i) + ch + w.substring(i+1);
Also, you will find it convenient to use a for loop in
which the loop control variable is a char:
for (char ch = 'a'; ch <= 'z'; ch++) { ...
For this week's lab, you will use two of the classes in the Java Collection Framework:...
For this week's lab, you will use two of the classes in the Java Collection Framework: HashSet and TreeSet. You will use these classes to implement a spell checker. Set Methods For this lab, you will need to use some of the methods that are defined in the Set interface. Recall that if set is a Set, then the following methods are defined: set.size() -- Returns the number of items in the set. set.add(item) -- Adds the item to the...
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