This note describes how to detect when ‘enter’ is pressed in an EditText field. It’s helpful for the prefix-word game, but possibly others as well.

Make your activity implement OnEditorActionListener:

public class MyActivity extends Activity
implements TextView.OnEditorActionListener {
    // ...
}

You’ll need to add the method onEditorAction:

public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
    // This method can be called when you press enter in an EditText
    // field. Returning true means we CONSUME the event, and it
    // doesn't perform its default action. You probably want to
    // ignore the DOWN event, and just respond to UP.
    if(event.getAction() != KeyEvent.ACTION_UP) return true;
    // Now you can do whatever else you want in response to
    // the key press.
    // ...
    return true;
}

You still have to install this handler in the onCreate method:

    editText = (EditText) findViewById(R.id.editText);
    editText.setOnEditorActionListener(this);

and here is how you can initialize the content of the field… both the text it contains, and the position of the cursor:

    editText.setText(goalPrefix);
    editText.setSelection(goalPrefix.length());

Dictionary

Now, I’ll include the code for the revised Dictionary class I created. It can now choose two-letter prefixes, eliminating those that have only a few words.

package com.example.words;

import java.io.*;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Random;

public class Dictionary {

    HashSet<String> hashSet = new HashSet<String>();
    HashMap<String, Integer> prefixes = new HashMap<String, Integer>();
    Random rng = new Random();

    public Dictionary(InputStream is) {
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String line1;
        int numWords = 0;
        try {
            line1 = br.readLine();
            while(line1 != null) {
                if(acceptableWord(line1)) {
                    if(line1.length() > 2) {
                        String prefix = line1.substring(0, 2);
                        Integer k = prefixes.get(prefix);
                        if(k == null) {
                            prefixes.put(prefix, 1);
                        } else {
                            prefixes.put(prefix, k+1);
                        }
                    }
                    hashSet.add(line1);
                    numWords++;
                }
                line1 = br.readLine();
            }
        } catch(IOException exn) {
            line1 = "ERROR!";
        }
        // temporary: show all prefixes
        for(String prefix : prefixes.keySet()) {
            int k = prefixes.get(prefix);
            if(k > 5) {
                System.out.println(prefix + " => " + prefixes.get(prefix));
            }
        }
    }

    public String choosePrefix() {
        int n = prefixes.size();
        int k = rng.nextInt(n);
        for(String prefix : prefixes.keySet()) {
            if(k == 0) {
                return prefix;
            }
            k--;
        }
        return "ERROR";
    }

    public boolean acceptableWord(String word) {
        for(int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            if(!Character.isLowerCase(c)) return false;
        }
        return true;
    }

    public boolean contains(String word) {
        return hashSet.contains(word);
    }

    public int getNumWords() {
        return hashSet.size();
    }


    public static void testWord(Dictionary d, String word) {
        System.out.println(word + ": " + d.hashSet.contains(word));
    }

    public static void main(String[] args) throws FileNotFoundException {
        System.out.println("Hello.");
        Dictionary d = new Dictionary(new FileInputStream("/usr/share/dict/words"));
        testWord(d, "elephant");
        testWord(d, "anvil");
        testWord(d, "koala");
        testWord(d, "aroceuhalcue");
        testWord(d, "junkkkk");
        testWord(d, "helllllllllllllllllllllllllo");

        System.out.println(d.hashSet.size() + "words");

        for(int i = 0; i < 10; i++) {
            System.out.println("Sample prefix: " + d.choosePrefix());
        }

    }
}

Here is the tail end of the output when we run Dictionary.main as a test program.

elephant: true
anvil: true
koala: true
aroceuhalcue: false
junkkkk: false
helllllllllllllllllllllllllo: false
64147words
Sample prefix: ke
Sample prefix: ep
Sample prefix: dé
Sample prefix: eu
Sample prefix: gi
Sample prefix: it
Sample prefix: la
Sample prefix: ll
Sample prefix: éc
Sample prefix: gr

We’ll probably want to find a way to eliminate those accented characters, so that prefixes like éc don’t show up… unless you’re playing the game in French!