疑問 - JAVA I/O問題

[burgh]

public static void main(String args[]) throws IOException
	   {
	      BufferedReader buf;
	      String str;

	      buf=new BufferedReader(new InputStreamReader(System.in));
	      System.out.print("Input a string:\n");
	      FileWriter fw=new FileWriter("a1.txt");
	      BufferedWriter bfw=new BufferedWriter(fw);

	      boolean isExit = false;
	      while(!isExit){

	    	  str=buf.readLine();

	    	  if(str != null && !"EXIT".equalsIgnoreCase(str)){
	    		  bfw.write(str);
			      bfw.newLine();
			      bfw.flush();
	    	  }else{
	    		  isExit = true;
	    	  }

	      }
	         fw.close();
	      }