Markov in Java

Markov.java

import java.nio.file.Path;
import java.util.List;
import java.util.Random;
import java.util.ArrayList;

public class Markov {

    /** Regular expression for breaking up words. */
    private static final String WORD_REGEX = "(?<=\\w\\W)";

    /** Regular expression for getting individual characters. */
    private static final String CHAR_REGEX = "(?<=.)";
    
    public static void main(String[] args) {
        StringChain sc = new StringChain(2);
        List<String> words = new ArrayList<String>();
        words.add("markov");
        words.add("chain");
        words.add("how");
        words.add("are");
        words.add("markov");
        words.add("chains");
        words.add("built");
        words.add("you");
        words.add("ask?");
        words.add("later");
        words.add("markov");
        words.add("chains");
        words.add("will");
        words.add("predict");
        words.add("text");
        sc.addItems(words.iterator());

        System.out.println( String.join(" ", sc.generate(10, new Random()) ) );
    }
    
    private static void addFile(StringChain chain, String regex, Path file) {
            
    }
    
}

StringChain.java

import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Random;
import java.util.stream.Collectors;

public class StringChain {
    private HashMap<String, List<Suffix>> map;
    private int ORDER;
    
    public StringChain(int order){
        ORDER = order;
        map = new HashMap<String, List<Suffix>>();
    }

    class Prefix {
        public String prefix;

        Prefix(List<String> pfx) {
            prefix = String.join("|+|", pfx);
        }
    }


    class Suffix {
        public String suffix;
        public int count;

        Suffix(String sfx) {
            suffix = sfx;
            count = 1;
        }

        void increaseCount() {
            count++;
        }
    }


    private List<String> initialPrefix() {
         ArrayList<String> prefix = new ArrayList<String>(ORDER);
        for(int i=0; i < ORDER; i++) {
            prefix.add("<BLANK>");
        }
        return prefix;
    }

    public void addItems(Iterator<String>itemIter) {
        List<String> prefix = initialPrefix();

        while(itemIter.hasNext()) {
            String suffix = itemIter.next();
            Prefix pfx = new Prefix(prefix);
            List<Suffix> sfxs = map.get(pfx.prefix);
            if(sfxs == null) {
                sfxs = new ArrayList<Suffix>();
                map.put(pfx.prefix, sfxs);
                sfxs.add(new Suffix(suffix));
            } else {
                // Suffix exists?
                Suffix existing = null;
                for(int i=0; i < sfxs.size(); i++) {
                    if(sfxs.get(i).suffix.equals(suffix)) {
                        existing = sfxs.get(i);
                        existing.increaseCount();
                        break;
                    }
                }
                if(existing == null) {
                    sfxs.add(new Suffix(suffix));
                }
            }
            prefix.remove(0);
            prefix.add(suffix);
        }
    }

    public List<String> generate(int n, Random rand) {
        List<String> prefix = initialPrefix();
        List<String> output = new ArrayList<String>(n);

        for(int i=0; i < n; i++) {
            String next = null;
            Prefix pfx = new Prefix(prefix);
            List<Suffix> sfxs = map.get(pfx.prefix);
            if(sfxs == null) {
                next = "<BLANK>";
            } else {
                // Pick from sfxs
                float sum=0;
                float r = rand.nextFloat();
                int picked = 0;
                for(int j=0; j < sfxs.size(); j++) {
                    Suffix s = sfxs.get(j);
                    sum += s.count;
                }
                for(int j=0; j < sfxs.size(); j++) {
                    Suffix s = sfxs.get(j);
                    float prob = (float)s.count / sum;
                    if(prob > r) {
                        picked = j;
                        break;
                    }
                }
                next = sfxs.get(picked).suffix;
            }
            if(next != null) {
                output.add(next);
                prefix.remove(0);
                prefix.add(next);
            }
        }
        
        return output;
    }


}