違いは何ですか
FileInputStream fstream = new FileInputStream ("file1.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
と
FileInputStream fstream = new FileInputStream ("file1.txt");
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
ここで本当に DataInputStream が必要ですか?