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I have a hashtable that contains the information about some book titles and the number of times each book is purchased. I want to draw a bar chart that can show this information visually. Is there any library or method in java that can do this?
HashTable<String, Integer> bookPurchaseTable=new HashTable<String, Integer>();
JavaFX has bar chart capabilities. This page has a tutorial that should have enough information to get you started.
https://docs.oracle.com/javafx/2/charts/bar-chart.htm
Also, You should probably use a HashMap instead of a HashTable if possible.
Use myHashMap.keySet() to get the keys, and then for each key, use myHashMap.get(key) to get the integer.
it's a big topic about Java UI deployment.
you can try java swing tutorial first, and learn how to develop UI in java.
BTW, it's recommend to use HashMap not HashTable now.
hope you can enjoy the Java.
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I'm trying to solve the following problem:
I have some expensive work to do which I then cache the result of
The work is keyed by a string
Many requests may arrive simultaneously for the same key
I'd like to avoid doing the work more than once per key
I'd like to add callbacks against the key which will be invoked when the work is completed; not all of these are known when the work is first submitted.
This feels like a problem which ought to have been solved already; does anybody know of a Java framework or library which covers it?
I can imagine a wrapper around guava's LoadingCache but I'm not aware of a library which does everything out of the box.
While LoadingCache#get is synchronous, it does get you 1-4 and there may be some mileage in using refresh which can return a ListenableFuture (although to get all the features you list it might become a fairly chunky wrapper?)
For Reference:
http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/cache/LoadingCache.html#refresh(K)
http://www.theotherian.com/2013/11/non-blocking-cache-with-guava-and-listenable-futures.html
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Where can I find more information on how exactly the following method works
and what it actually does? I found the single line of the documentation leaves a bit to be desired:
Class weka.associations.Apriori
public void buildAssociations(Instances instances) throws Exception
Method that generates all large itemsets with a minimum support, and from these all association rules with a minimum confidence.
Look at all the documentation, not only the method documentation tooltip in your IDE. You are missing out on a lot of the documentation.
Weka comes with a whole book, that will give you plenty of detail.
The Apriori class documentation also contains much more than that single line you quoted. You failed to access the JavaDoc class documentation; it's not the documentation that "leaves a bit to be desired", is it? It points to two publication giving the details on the algorithm.
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I am a complete newbie to Java programming and I am trying to learn caching and hash tables. I have seen tutorials online but they are complex, does anyone here know of any relatively short programs that utilise caching and hash tables?
Thanks for any help given
UPDATE:
I am basically starting from scratch. I know hash tables and sort of know caching (more simple caching programs would be much appreciated), but I don't get how the two work together. For example saving to a hash table and caching the data.
As the comments mention, a cache is just a store where you keep the output so you won't have to do the calculation again.
Here's a really simple example
Map<String,Double> answers = new HashMap<String,Double>();
// checking cache if we have the answer
If (answers.get("volatility") != null) {
System.out.println("volatility found in cache:" +
answers.get("volatility"));
}
// store a value in cache
answers.put("rate",1.887);
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I am going to start a project on Markov Decision Processes and am starting up a basic framework to work in. The first thing I want to set up is a grid of n by n, with cells which are empty or occupied by some class of agents (lets say a monkey, banana and palm tree). I want to be able to visualize this with JAVA. But am actually hoping that I will not have to write the code from scratch, i.e. the visualization part.
So, a grid of n by n, with (possible) some word, picture or number in each cell. Any ideas on existing packages?
I think you can use a JTable
http://docs.oracle.com/javase/7/docs/api/javax/swing/JTable.html
http://docs.oracle.com/javase/tutorial/uiswing/components/table.html
Setting the appropiate TableCellRenderer you can display each cell the way you like.
The problem is that you have to write some code.
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I have a list of words in a text file. What I want is for an input word a list of words that are similar to the input word. So the program should work similar to a spell checker API with only thing that the dictionary is limited to my list of words.
I can write my own code if I get some pointers to Spell Checker algorithm or regular expressions.
Take a look at Apache Commons Lang StringUtils.getLevenshteinDistance. The Levenshtein algorithm gives the "edit distance" between two words, that is, how similar they are. Their implementation is quite fast - I tested it against another implementation I found online and it was about 1/3 faster if I remember correctly.
I highly recommend taking a look at Peter Norvig's article on How to Write a Spelling Corrector. It's worth reading. And it doesn't involve too much of a complexity. If you scroll down the page, you can see links to Java implementations. Then, you can customize it to your own needs.
http://en.wikipedia.org/wiki/Levenshtein_distance