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Java Forum / First Aid / July 2007Is there a better way to do this?
I gave it a shot, to answer the question that that person posted here a couple of days ago Create a java program that generates 10000 random integer numbers between 1 and 500. Then use the generated numbers to calculate: - the mean (average) of all numbers - the standard deviation - the largest and smallest number - the median number (50% is above it, 50% is below it) - the mode (the number(s) that occurs most frequently) The hardest part was the "mode" part. At first I thought I'd use arrays, but then I realized that using an ArrayList<Integer> would let me use the various methods associated with the Collections class So I wrote my program, tested it with some small numbers. It looks ok, and when I run it with 10000 occurances of randoms 1-500 I get decent results. And it does answer the question, so I'd probably get 50% on it for sure. But is it wel written? And I don't mean comments. I mean does it follow the OO rules? I put one static method in to fill up the ArrayList of randoms, but can I take it further? Or is there a point where you've over-done it? Anyway, here's a link to my code. I'd appreciate any comments or critisim. I think it's a good first attempt, but it's not something I'd want to turn in to a professor, yet. http://sparklesthecat.is-a-geek.com/code/Hello.java I know it's not a very imaginative name, but it's not going on the market.  SignatureJohn T. My other computer is a swodniw machine 2007 >Anyway, here's a link to my code. I'd appreciate any comments or critisim. I think it's a good first attempt, but it's not something I'd want to turn in to a professor, yet. > >http://sparklesthecat.is-a-geek.com/code/Hello.java ArrayLists are for when you don't know in advance how many elements you will have. Arrays are for when you do. If you flip your code from ArrayList to Array you will see it becomes much more readable and faster. Not to worry about the loss of Collections.sort. See Arrays.sort. See http://mindprod.com/jgloss/sort.html also try to convert any FOR to for:each.. That greatly enhances readability. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com >>Anyway, here's a link to my code. I'd appreciate any comments or critisim. I think it's a good first attempt, but it's not something I'd want to turn in to a professor, yet. >> [quoted text clipped - 10 lines] > also try to convert any FOR to for:each.. That greatly enhances > readability. Yeah, I knew I could have implemented a bubble sort or insertion sort or something like that, but the Collections.sort lets me do it in one line. And thanks for the tip about for:each I knew there was something like that but I didn't feel like looking it up :-) >Yeah, I knew I could have implemented a bubble sort or insertion sort or >something like that, but the Collections.sort lets me do it in one line. so does Arrays.sort which sorts arrays. See http://mindprod.com/jgloss/sort.html There is no need to roll your own sort to sort arrays. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > I gave it a shot, to answer the question that that person posted here a couple of days ago > [quoted text clipped - 17 lines] > > I know it's not a very imaginative name, but it's not going on the market. As well as being unimaginative, it allowed you to avoid deciding the primary purpose of the class. One of the first tests of a "good" class is that it is easy to name, because it has a known purpose. In this case, I think Hello combines two jobs: 1. A statistics calculator. 2. A test wrapper that supplies the statistics calculator with a List of random numbers and prints results. The test wrapper could be tucked away in the main method of the statistics calculator, but I think it should be separated out so that the statistics calculator could be used to analyze an arbitrary List<Integer>. Patricia >> I gave it a shot, to answer the question that that person posted here a couple of days ago >> [quoted text clipped - 35 lines] > > Patricia Agreed. Time for a re-factoring. One class does one thing and one thing well. This class does several things. Thanks for the hint. New version of programs StatPackTester.java (invokes StatisticsPackage and displays results) http://sparklesthecat.is-a-geek.com/code/StatPackTester.java StatisticsPackage.java (does all the work) http://sparklesthecat.is-a-geek.com/code/StatisticsPackage.java I don't think there are any magic values, although some of the class variables have obscure names. Cheers SignatureJohn T. My other computer is a swodniw machine 2007 > New version of programs > [quoted text clipped - 7 lines] > I don't think there are any magic values, although some of the > class variables have obscure names. If a variable name is unclear, consider renaming the variable something clearer, or at worst, add a comment explaining what the variable is for. Also note that the term "Package" has a very specific meaning in Java, and I was thrown off when I saw your class was called "StatisticsPackage". - Oliver > I gave it a shot, to answer the question that that person posted here a couple of days ago > [quoted text clipped - 6 lines] > - the median number (50% is above it, 50% is below it) > - the mode (the number(s) that occurs most frequently) Snippet from the code: for (int y=0;y<totalNumberOfDraws;y++) { stdDev = stdDev + (((double)listOfRandomNumbers.get(y) - median) * ((double)listOfRandomNumbers.get(y) - median)); } stdDev = stdDev/5; stdDev = Math.sqrt(stdDev); 1. Why based on median, rather than mean? 2. Why divide by magic constant "5"? (By "magic constant" I mean a number that just appears in the code, with no explanation.). Patricia > 1. Why based on median, rather than mean? I looked up a formula on the internet and it told me to use the mean, and I mis-read it as media. Is mean the same as average? I haven't done stats in a long time. > 2. Why divide by magic constant "5"? (By "magic constant" I mean a > number that just appears in the code, with no explanation.). Typo.. sorry... s/b totalNumberOfDraws SignatureJohn T. My other computer is a swodniw machine 2007 >> 1. Why based on median, rather than mean? > > I looked up a formula on the internet and it told me to use the mean, > and I mis-read it as media. Is mean the same as average? I haven't > done stats in a long time. The term "average" is usually used to for the "mean". "Mean" is more precise. Your "average" calculation is correct for getting the mean. Patricia >I gave it a shot, to answer the question that that person posted >here a couple of days ago [quoted text clipped - 7 lines] > - the median number (50% is above it, 50% is below it) > - the mode (the number(s) that occurs most frequently) [...] > So I wrote my program, tested it with some small numbers. [...] > But is it wel written? And I don't mean comments. I mean does > it follow the OO rules? For some problems, OO is the best tool for the job. For this problem, I don't think OO is the best tool for the job. The problem specification reads like a recipe, listing each step to be performed, and the order in which to perform those steps. It is extremely natural to translate the problem description almost directly into a procedural (i.e. non-OO) program. - Oliver > For some problems, OO is the best tool for the job. For this problem, > I don't think OO is the best tool for the job. The problem specification [quoted text clipped - 4 lines] > > - Oliver So what is the point of using Java if you aren't going to employ OO techniques? I could have written it in Cobol, or Fortran or even... gasp... C (well maybe not in C as fast as I could in Cobol) the assignment was in a Java class :-) And I didn't interpret the assignment as do this, then this, then this.... all I saw was a bunch of results that the instructor wanted out the other end. And the only pre-requisite that I could see was that the mean had to be computed before the stdDev as it was used. Although, it would have been just as easy to include a computation of the mean in the section that does stdDev, or better yet, call the setStdDev method within.. but that seemed like overkill to me. So I simply pass the mean into the stdDev method. Anyways, it was an interesting exercise. My first program was a piece of crap and it had bugs in it (thanks for spotting them Patricia). I think my new program is pretty good, although there are probably improvements to be made. My next iteration will probably make some of them. "JT" <jtlinux1@oohay.ca> wrote... >> For some problems, OO is the best tool for the job. For this problem, >> I don't think OO is the best tool for the job. The problem specification [quoted text clipped - 7 lines] > So what is the point of using Java if you aren't going > to employ OO techniques? Simply because it can be done? ;-) Many programming classes, "focusing" on different languages, are overlapping in terms of fundamental algorithmic thinking. This type of excercise is useful regardless of which programming language that is taught. What many classes (teachers) usually miss, is to point out the differences between different solutions; how different languages and programming paradigms connect to each other, and the consequences of that. /// Bjorn A Free MagazinesGet these publications absolutely FREE for up to 12 months. 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