How to replace HashMap<String, Integer> with an array?

Question

I have a program that count occurrences of words in given array. It keeps words and its quantity. For example, in given array:

String array[] = {"cat", "dog", "cat"};

I have 2 cats, and 1 dog. Making it with HashMap is quite simple:

HashMap<String, Integer> map = new HashMap<>();
for (int i = 0; i < wordarray.length; i++) {
    String word = wordarray[i].toLowerCase();
    if (map.containsKey(word)) {
        map.put(word, map.get(word) + 1);
    } else {
        map.put(word, 1);
    }
}

Then I just need to print it out:

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey() + " : " + entry.getValue());
}

But is there any way to make it without HashMap only using arrays of objects?

The reason why a HashMap is used is because it has unique keys like a Set. This way you can check if the String you are looking for exists, without having to loop over an entire Array. — Mr. Polywhirl
– Mr. Polywhirl, Commented Jun 17, 2013 at 15:53
Implement/reuse hash table with open addressing (en.wikipedia.org/wiki/Open_addressing)? — Alex Nikolaenkov
– Alex Nikolaenkov, Commented Jun 17, 2013 at 16:00

Oscar · Accepted Answer · 2013-06-17 15:49:16Z

4

Create a custom class to hold your string and int values, and then use an array to hold them. In pseudo-code:

class Myclass
 public int myInt;
 public string MyString;
 //Constructor omited..


//Somewhere else..
MyClass[] my = new Myclass[2];
my[0] = new MyClass("string", 1);

answered Jun 17, 2013 at 15:49

Oscar

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1 Comment

mazix Over a year ago

nice one :) I will try it!

duffymo · Accepted Answer · 2013-06-17 15:49:35Z

3

You can create a list/array of Map.Entry key/value pairs.

There's already a method to do it for you in HashMap: entrySet()

http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html#entrySet()

answered Jun 17, 2013 at 15:49

duffymo

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1 Comment

duffymo Over a year ago

Nope, that's lazy - a quality in the best programmers.

Victor Sorokin · Accepted Answer · 2013-06-17 15:57:34Z

This much-much slower than using HashMap, but it should work:

Let's say, you sure that no word occurs in your text more than N times (as a upper bound you can choose total number of words in text). Then you can allocate array of that size N of ArrayList elements: a = new ArrayList[N]; for (int i = 0; i < N; i++) a[i] = new ArrayList<String>();

Then, for every word w, you will iterate over that array, find the cell with index c with ArrayList<String> which contains w and move w from c to c+1 (using list.remove(Object) and list.add(Object)). If no cell found, add w to the list in the first cell: a[0].add(w).

Some optimizations:

use HashSet in array instead of ArrayList, though it looks inappropriate in your case;
use array of arrays of [N][N] size. There will be more memory consumption, but less time spent.

stinepike · Accepted Answer · 2013-06-17 16:32:57Z

1

you can check the implementation of Map using arrays. Here is a nice article about this

answered Jun 17, 2013 at 16:32

stinepike

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