[Java] Name That Number

/* Use the slash-star style comments or the system won't see your
   identification information */
/*
ID: lincans1
LANG: JAVA
TASK: namenum
*/
import java.io.*;
import java.util.*;

public class namenum {
     

	private String number;
	private Map<Character, String> map;
	private Set<String> set;
	private boolean flag;

	private void dfs(int i, StringBuilder b, PrintWriter out) {
     
		if (i == number.length()) {
     
			if (set.contains(b.toString())) {
     
				flag = false;
				out.println(b.toString());
			}
			return;
		}
		for (char ch : map.get(number.charAt(i)).toCharArray()) {
     
			b.setCharAt(i, ch);
			dfs(i + 1, b, out);
		}
	}

	public namenum() throws IOException {
     

		map = new HashMap<>();
		map.put('2', "ABC");
		map.put('3', "DEF");
		map.put('4', "GHI");
		map.put('5', "JKL");
		map.put('6', "MNO");
		map.put('7', "PRS");
		map.put('8', "TUV");
		map.put('9', "WXY");

		// Use BufferedReader rather than RandomAccessFile; it's much faster
		BufferedReader f = new BufferedReader(new FileReader("namenum.in"));
		PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("namenum.out")));
		this.number = f.readLine();

		set = new HashSet<>();
		BufferedReader reader = new BufferedReader(new FileReader("dict.txt"));
		String word = null;
		while ((word = reader.readLine()) != null) {
     
			if (word.length() == number.length()) {
     
				set.add(word);
			}
		}
		
		flag = true;
		dfs(0, new StringBuilder(number), out);
		if (flag) {
     
			out.println("NONE");
		}
	    out.close();                                  // close the output file
	}
	
	public static void main (String [] args) throws IOException {
     
		new namenum();
	}
}