The Big Programming Thread - Page 298

On May 10 2013 07:47 thOr6136 wrote:
Hey, i have a problem.

So, java. Summing up a task first: 300 txt files with dates and temperatures over 10 years. I have to read all the temperatures and add them into maps with different kind of keys, for value we use List<Double> for storing temperatures. So basically we have to make 4 kind of maps with different kind of keys. One key is Location (name of file) other one is Location + year etc. After that we have to make another set of maps - keys equivalent to the ones before only values have to be different. This time we need double array (List before) with 2 values in it, one is an average value of all temperatures in that list (from map from before). Now here i have a problem.

I use a method for generating a new HashMap with same keys as before but different kind of values (double arrays). The problem is, when i add keys to the new map i am creating (i use put(key, value)) it overwrites values from before but the key is completely different. It shouldn't happen because put method always compares 2 keys with equals() method and it compares hashCode(). When i debug the key that i input in put method is always different, but values get overwritten each time. It's so strange... Anyway i can post a code of this part:

    public static HashMap<String, double[]> averages(HashMap<String, List<Double>> map)
    {
        HashMap<String, double[]> mapAverage = new HashMap<>();
        double[] x = new double[2];
        
        for(Map.Entry<String, List<Double>> entry : map.entrySet())
        {
            // if i System.out.println(key); all keys are different
            String key = entry.getKey();
            //used to generate average number of all temperatures in list
            x[0] = povprecje(entry.getValue(), key);
            //used to generate something else
            x[1] = odmik(entry.getValue(), key, x[0]);
            mapAverage.put(key, x);
        }
        return mapAverage;
    }

Is there anything that could make overwriting all the values from before in map? Or am i missing something in this part?

On May 11 2013 04:47 darkness wrote:
I'm curious what the most useful/efficient approach is when it comes to using threads.

A. Cached pool like - http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/Executors.html#newCachedThreadPool() (you re-use threads)
B. Worker/dispatcher threads
C. Fixed thread pool like - http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool(int)
D. Other (specify please)

I guess it depends on the application, e.g. you may want worker/dispatcher threads for servers, while cached pool could work for desktop & servers.

On May 12 2013 04:42 GunSec wrote:
btw, I am also wondering if I can pm some of the moderators of this thread or the creator? I have some personal stuff I want to talk about in programming and computer science in general !