java字符流练习，读文件，将其内容每行倒序写到另一文件

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;

import javax.annotation.processing.Filer;
import javax.lang.model.element.Element;
import javax.tools.FileObject;
import javax.tools.JavaFileObject;
import javax.tools.JavaFileManager.Location;

public class Test1 {

private static final String NUll = null;

/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
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();
}

}