Java Comparator for alternate string sorting

Question

EDIT: The comparator doesn't seem to be doing anything. I get no errors but the (already alphabetically sorted) array isn't changing. I should expect to see SAD and PAD beside each other but I am not.

I have an array of strings and I want to sort them based on their numerical value derived from how to type them out on a dial pad. That is, "SAD" = 723, "PAD" = 723, "SAP" = 727. I have an alphabetically ordered dictionary and I want to rearrange it into my order in order to do a binary search on the array. For things like SAD and PAD being the same value, they can be then sorted alphabetically. I want to try to use Arrays.sort(dictionary, myComparator) to sort it.

First, would this be the best way to go about getting what I want? How else might I get this?

Second, how do I make my own comparator? Note that I am just in a first course in programming so we aren't even making classes yet, it's all just a bunch of stuff crammed into a main class. And I generally don't know about classes at all. So if I would have to go and make my own class to make this work, then I will probably have to code a quicksort myself instead. I haven't covered linked lists either so my data structure is a bit clumsy. Here is what I have so far and I have no idea what I am doing:

Stupid clumsey way to get the dictionary into memory, important line is near bottom:

public static String[][] dictToMem()throws FileNotFoundException{
    File myFile = new File("src/words.txt");
    Scanner input = new Scanner(myFile);
    String temp;
    String[] tempDict = new String[7];
    Arrays.fill(tempDict, "");

    while (input.hasNext()){
        temp = input.next();
        if (temp.length() < 8 && temp.indexOf('\'') + temp.indexOf('(') +   temp.indexOf('-') == -3){
            for (int i = 1; i <= 7; i++){
                if (temp.length() == i){
                    tempDict[i-1] += " " + temp;
                }
            }
        }
    }
    for (int i = 0; i<tempDict.length; i++){
        tempDict[i] = tempDict[i].trim();
    }

    String[][] dictionary = new String[7][];
    for (int i = 0; i<tempDict.length; i++){
        dictionary[i] = tempDict[i].split(" ");
    }
    for (int i = 0; i<tempDict.length; i++){
        //  ***This is the line doesn't work, compiler error***
        //  dictionary[i] = Arrays.sort(dictionary[i], String.DialPadNumCompare);
        //  Should be this:
        Arrays.sort(dictionary[i], DialPadNumCompare);
    }
    return dictionary;
}

And the comparator isn't showing an error:

public static Comparator<String> DialPadNumCompare = new Comparator<String>(){
    @Override
    public int compare(String a, String b){
        if (stringToInt(a) == stringToInt(b)){
            return a.compareTo(b);
        }
        return stringToInt(b) - stringToInt(a);
    }
};

String to int is my string to dial pad number converting method

cannot find symbol symbol: variable DialPadNumCompare location: class String — fhyve
– fhyve, Commented Nov 25, 2012 at 5:43
Try to adhere to java naming conventions of variable names start with lower case — Bohemian
– Bohemian ♦, Commented Nov 25, 2012 at 5:57
@ Bohemian Where did I not do that? Is "DialPadNumCompare" a variable? — fhyve
– fhyve, Commented Nov 25, 2012 at 6:01
The sort with comparator is not doing anything. The program runs and goes through the sort but the dictionary looks the same before and after the sort, where I should be seeing BAN and CAN together. And why did I get downvoted? — fhyve
– fhyve, Commented Nov 25, 2012 at 6:03

anubhava · Accepted Answer · 2012-11-25 06:57:32Z

3

Your comparator is not correct. Change it to:

public static Comparator<String> dialPadNumCompare = new Comparator<String>(){
    @Override
    public int compare(String a, String b){
        int inta = stringToInt(a);
        int intb = stringToInt(b);
        if (inta == intb)
            return a.compareTo(b);
        return inta - intb;
    }
};

And call this comparator using this code:

Arrays.sort(dictionary, dialPadNumCompare);

Here is Live Demo

answered Nov 25, 2012 at 6:57

anubhava

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Perception · Accepted Answer · 2012-11-25 05:36:56Z

0

For your immediate error, change the line:

Arrays.sort(dictionary[i], String.DialPadNumCompare);

To:

Arrays.sort(dictionary[i], DialPadNumCompare);

The way you have it now, you are trying to statically reference a non-existent member of the String class. Instead you should be trying to reference the static reference DialPadNumCompare that you created in your own class.

answered Nov 25, 2012 at 5:36

Perception

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2 Comments

fhyve Over a year ago

Now I'm getting a problem that probably doesn't have to do with the comparator. Doing the change you suggest gives this: incompatible types required: String[] found: void. Also, the condition on that for loop should be i<dictionary[i].length, not tempDict.length

Perception Over a year ago

The Arrays class does a sort-in-place, and doesn't have a return type. Change your line dictionary[i] = Arrays.sort(dictionary[i], DialPadNumCompare); to Arrays.sort(dictionary[i], DialPadNumCompare);

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