Simple Markov chain text generator

markov.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Hashtable;
import java.util.Random;
import java.util.Vector;


public class Markov {

	// Hashmap
	public static Hashtable<String, Vector<String>> markovChain = new Hashtable<String, Vector<String>>();
	static Random rnd = new Random();
	
	
	/*
	 * Main constructor
	 */
	public static void main(String[] args) throws IOException {
		
		// Create the first two entries (k:_start, k:_end)
		markovChain.put("_start", new Vector<String>());
		markovChain.put("_end", new Vector<String>());
		
		while(true) {
		// Get some words 
		System.out.print("Enter your phrase > ");
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String sInput = in.readLine() + ".";
		
		// Add the words to the hash table
		addWords(sInput);
		}
		
	}
	
	/*
	 * Add words
	 */
	public static void addWords(String phrase) {
		// put each word into an array
		String[] words = phrase.split(" ");
				
		// Loop through each word, check if it's already added
		// if its added, then get the suffix vector and add the word
		// if it hasn't been added then add the word to the list
		// if its the first or last word then select the _start / _end key
		
		for (int i=0; i<words.length; i++) {
						
			// Add the start and end words to their own
			if (i == 0) {
				Vector<String> startWords = markovChain.get("_start");
				startWords.add(words[i]);
				
				Vector<String> suffix = markovChain.get(words[i]);
				if (suffix == null) {
					suffix = new Vector<String>();
					suffix.add(words[i+1]);
					markovChain.put(words[i], suffix);
				}
				
			} else if (i == words.length-1) {
				Vector<String> endWords = markovChain.get("_end");
				endWords.add(words[i]);
				
			} else {	
				Vector<String> suffix = markovChain.get(words[i]);
				if (suffix == null) {
					suffix = new Vector<String>();
					suffix.add(words[i+1]);
					markovChain.put(words[i], suffix);
				} else {
					suffix.add(words[i+1]);
					markovChain.put(words[i], suffix);
				}
			}
		}		
		generateSentence();
	}
	
	
	/*
	 * Generate a markov phrase
	 */
	public static void generateSentence() {
		
		// Vector to hold the phrase
		Vector<String> newPhrase = new Vector<String>();
		
		// String for the next word
		String nextWord = "";
				
		// Select the first word
		Vector<String> startWords = markovChain.get("_start");
		int startWordsLen = startWords.size();
		nextWord = startWords.get(rnd.nextInt(startWordsLen));
		newPhrase.add(nextWord);
		
		// Keep looping through the words until we've reached the end
		while (nextWord.charAt(nextWord.length()-1) != '.') {
			Vector<String> wordSelection = markovChain.get(nextWord);
			int wordSelectionLen = wordSelection.size();
			nextWord = wordSelection.get(rnd.nextInt(wordSelectionLen));
			newPhrase.add(nextWord);
		}
		
		System.out.println("New phrase: " + newPhrase.toString());	
	}
}

public static Hashtable<String, Vector> markovChain = new Hashtable<String, Vector>();

=> error : The field markovChain cannot be declared static; static fields can only be declared in static or top level types

Can you explain this error, I'm using processing

where are the libraries to import (hashtable & vector)

Thanks for posting this. By looking through it, I was able to gain a better understanding of the basic Markov chain model.