使用HashMaps的字数统计程序

Question

import java.io.*;
import java.util.*;

public class ListSetMap2 
{
    public static void main(String[] args)
    {
        Map<String, Integer> my_collection = new HashMap<String, Integer>();
        Scanner keyboard = new Scanner(System.in);

        System.out.println("Enter a file name");
        String filenameString = keyboard.nextLine();
        File filename = new File(filenameString);
        int word_position = 1;
        int word_num = 1;

        try
        {
            Scanner data_store = new Scanner(filename);
            System.out.println("Opening " + filenameString);
            while(data_store.hasNext())
            {
                String word = data_store.next();
                if(word.length() > 5)
                {
                    if(my_collection.containsKey(word))
                    {
                        my_collection.get(my_collection.containsKey(word));
                        Integer p = (Integer) my_collection.get(word_num++);
                        my_collection.put(word, p);
                    }
                    else
                    {
                        Integer i = (Integer) my_collection.get(word_num);
                        my_collection.put(word, i);
                    }
                }
            }
        }
        catch (FileNotFoundException e)
        {
            System.out.println("Nope!");
        }
    }
}

I'm trying to write a program where it inputs/scans a file, logs the words in a HashMap collection, and count's the times that word occurs in the document, with only words over 5 characters being counted.

It's a bit of a mess in the middle, but I'm running into issues on how to count the number of times that word occurs, and keeping a individual count for each word. I'm sure there is a simple solution here and I'm just missing it. Please help!

Answer 1

Your logic of setting the frequency of word is wrong. Here is a simple approach that should work for you:

    // if the word is already present in the hashmap
    if (my_collection.containsKey(word)) {
        // just increment the current frequency of the word
        // this overrides the existing frequency
        my_collection.put(word, my_collection.get(word) + 1);
    } else {
        // since the word is not there just put it with a frequency 1
        my_collection.put(word, 1);
    }

Answer 2

(Only giving hints, since this seems to be homework.) my_collection is (correctly) a HashMap that maps String keys to Integer values; in your situation, a key is supposed to be a word, and the corresponding value is supposed to be the number of times you have seen that word (frequency). Each time you call my_collection.get(x) , the parameter x needs to be a String , namely the word whose frequency you want to know (unfortunately, HashMap doesn't enforce this). Each time you call my_collection.put(x, y) , x needs to be a String , and y needs to be an Integer or int , namely the frequency for that word.

Given this, give some more thought to what you're using as parameters, and the sequence in which you need to make the calls and how you need to manipulate the values. For example, if you've already determined that my_collection doesn't contain the word, does it make sense to ask my_collection for the word's frequency? If it does contain the word, how do you need to change the frequency before putting the new value into my_collection ?

(Also, please choose a more descriptive name for my_collection , eg frequencies .)

Answer 3

Try this way -

while(data_store.hasNext()) {

                String word = data_store.next();

                   if(word.length() > 5){

                    if(my_collection.get(word)==null) my_collection.put(1);
                    else{
                       my_collection.put(my_collection.get(word)+1);
                    }

                }
}