Тестил с разными вводами....
package com.javarush.task.task19.task1907;
/*
Считаем слово
*/
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
FileReader file = new FileReader(r.readLine());
BufferedReader reader = new BufferedReader(file);
StringBuilder s = new StringBuilder();
String line;
while((line = reader.readLine()) != null){
s.append(line);
s.append("\n");
}
String q = s.toString();
Pattern pattern = Pattern.compile("world");
Matcher matcher = pattern.matcher(q);
int i = 0;
while(matcher.find())
i++;
System.out.print(i);
r.close();
reader.close();
file.close();
}
}