java输入输出流FileReader，FileWriter，BufferedReader

1. `FileReader fr = new FileReader(“xxx.txt”);
   int len;
   while((len = fr.read()) != -1){
   System.out.print((char)len);
   }

   fr.close();`
   

2. `BufferedReader br = new BufferedReader(new FileReader(“xxx.txt”));
   BufferedWriter bw = new BufferedWriter(new FileWriter(“o.txt”));
   int b;
   while((b = br.read()) != -1){
   bw.write(b);
   }

   String str;
   while((str = br.readLine()) != NULL){
       bw.write(str);
       bw.newLine();
   }
   br.close();
   bw.close();`
   

3. BufferedReader br = new BufferedReader(new FileReader("xxx.txt"));
BufferedWriter bw = new BufferedWriter(new FileWriter("oooo.txt"));
ArrayList<String> list = new ArrayList<>();
String line;
while((line = br.readLine()) != NUll){
list.add(line);
}
for(int i = list.size() - 1;i >= 0 ;i--){
bw.write(list.get(i));
bw.newLine();
}
br.close();
bw.close();