Question

I am working on a simple project that obtains data from an input file, gets what it needs and prints it to a file. I am basically getting word frequency so each key is a string and the value is its frequency in the document. The problem however, is that I need to print out these values to a file in descending order of frequency. After making my hashmap, this is the part of my program that sorts it and writes it to a file.

//Hashmap I create
Map<String, Integer> map = new ConcurrentHashMap<String, Integer>();
int valueMax = -1;
//function to sort hashmap
while (map.isEmpty() == false){
            for (Entry<String, Integer> entry: map.entrySet()){
                if (entry.getValue() > valueMax){
                    max = entry.getKey();
                    System.out.println("max: " + max);
                    valueMax = entry.getValue();
                    System.out.println("value: " + valueMax);
                }
            }
            map.remove(max);
            out.write(max + "\t" + valueMax + "\n");
            System.out.println(max + "\t" + valueMax);  
        }   

When I run this i get:

t 9
t 9
t 9
t 9
t 9
....

so it appears the remove function is not working as it keeps getting the same value. I’m thinking i have an issue with a scope rule or I just don’t understand hashmaps very well.

If anyone knows of a better way to sort a hashmap and print it, I would welcome a suggestion.

thanks

Answer 1

Your code doesn’t work because on every subsequent iteration, entry.getValue() > valueMax is never true because you don’t reset valueMax on re-entry into the while loop.

You don’t need to muck around with double-looping over a concurrently accessible map though.

ConcurrentSkipListMap has a lastKey method that returns the greatest key and doesn’t require iteration over the entire map.