把一个file对象的内容带上行号复制到另一个file对象（java）

import java.io.*;
public class CopyFileAddLineNumber {
    public static void main (String[] args) {
        String infname = "CopyFileAddLineNumber.java";
        String outfname = "CopyFileAddLineNumber.txt";
        if( args.length >= 1 ) infname = args[0];
        if( args.length >= 2 ) outfname = args[1];

        try {
            File fin = new File(infname);
            File fout = new File(outfname);

            BufferedReader in = new BufferedReader(new FileReader(fin));
            PrintWriter out  = new PrintWriter(new FileWriter(fout));

            int cnt = 0;    // 行号
            String s = in.readLine();
            while ( s != null ) {
                cnt ++; 
                s = deleteComments(s);                      //去掉以//开始的注释
                out.println(cnt + ": \t" + s );             //写出
                s = in.readLine();                          //读入
            }           
            in.close();             // 关闭缓冲读入流及文件读入流的连接.
            out.close();
        } catch (FileNotFoundException e1) {
            System.err.println("File not found!" );
        } catch (IOException e2) {
            e2.printStackTrace();
        }
    }

    static String deleteComments( String s ) //去掉以//开始的注释
    {
        if( s==null ) return s;
        int pos = s.indexOf( "//" );
        if( pos<0 ) return s;
        return s.substring( 0, pos );
    }
}

java.nio.file.Files中有readAllLines()方法

import java.nio.file.*;
import java.nio.charset.*;
import java.util.List;

class ReadAllLines
{
    public static void main(String[] args) throws java.io.IOException
    {
        String filePath = "d:\\javaExample\\ch09\\ReadAllLines.java";

        List<String> lines = Files.readAllLines(
            Paths.get(filePath),  
            Charset.forName("utf8") //or Charset.defaultCharset()
        );
        for(String s : lines ) System.out.println(s);
    }
}

若对字节流 字符流 节点流 过滤流概念不清楚可查看前一篇博客~