java 修改txt文件中某一行的内容

对文档修改某一行，需要读进来，修改，然后再写进去。最快的方法就是边读边写。

import java.io.*;
public class Modifytxt{
    public static void main(String args[])throws IOException{
        int modifyline=1;//要修改的行
        BufferedReader in=new BufferedReader(new FileReader("1.java"));
        PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("2.java")));
        String line;
        int count=1;
        while((line=in.readLine())!=null){
            if(count==modifyLine){
                out.println(line.replace('abc', 'def'));  //替换abc成def
            }else{
                out.println(line);
            }
            count++;
        }
        in.close();
        out.close();
    }
}