Count same word from many file in directory

Hi! i'm beginner in java programming. i need count same word from many files, example:
doc1 : boys like to play football
doc2 : girls play tennis
doc3 : almost all boys and girls play tennis

lets say my program read doc1 and first word is "boys", now my program will check if "boys" is also appeared in another document, if appeared, count the word "boys". And it will check second word "like" is also appeared in another document or not, if not appeared, remove that word. And i need output is the filename and the word that appeared in another document.

Any code or example? please, i really need code example.
thank's for your answer and sorry for my bad english.

What have you done so far?

this is what i'v done but i think it didn't work

public class FWS {

public static void main(String[] args) throws Exception {

HashMap<String, Integer> wordFile = new HashMap<String, Integer>();
File directory = new File ("c:/document/");
File files[] = directory.listFiles();
for (File f : files) {
FileInputStream fis = new FileInputStream(f);
BufferedReader in = new BufferedReader(new InputStreamReader(fis));

String inputText = "";
inputText = in.readLine().toLowerCase();
BufferedReader line = new BufferedReader(new FileReader(inputText));
StreamTokenizer st = new StreamTokenizer(line);
st.resetSyntax();
st.wordChars('A', 'Z');
st.wordChars('a', 'z');

int freq = StreamTokenizer.TT_WORD;
while ((freq != StreamTokenizer.TT_EOF)) {
freq = st.nextToken();
if (freq == StreamTokenizer.TT_WORD){
String token = st.sval;
if (wordFile.get(token) == null) {
wordFile.put(token, 1);
}
else {
wordFile.put(token, wordFile.get(token) + 1);
}
}
}
System.out.println("Word: " + wordFile.size());
}
}

}

it's error while read files in directory,,,

1.) You don't need to use FileInputStream. Just BufferedReader and FileReader are sufficient for reading text files.
2.) Don't use StringTokenizer. Use the String.split method instead to split the lines into arrays of words.
3.) Make sure you write down the steps before writing the program. Think about how you would do it manually and then translate that into an algorithm which will later become your program.

thanks for your advice