编写一个程序，将一个文本文件的内容按行读出，每读出一行就顺序加上行号，并写入 到另一个文件中。

实验九 Java 语言的输入输出与文件处理
实验目的
1．了解流式输入输出的基本原理。
2．掌握 File、FileInputStream、FileOutputStream 类的使用方法。
3．掌握 FileReader、FileWriter、BufferedReader 类的使用方法。
主要仪器设备及耗材
安装了 JDK1.8 的 PC 一台
实验内容
2. 编写一个程序，将一个文本文件的内容按行读出，每读出一行就顺序加上行号，并写入
到另一个文件中。

src/com/temp/ShowLineNumBeforEachLine.java 

package com.temp;

import java.io.*;

/**
 * @Author lanxiaofang
 * @email 983770299@qq.com
 * @date 2020/11/16 9:18
 */
public class ShowLineNumBeforEachLine {

    private final static String url_1 = "D://word1.txt";
    private final static String url_2 = "D://word2.txt";

    //use BufferedReader and BufferedWriter
    public static void main(String[] args) {

        useBufferedWriter(url_1, url_2);

    }

    
    /**
     * useBufferedWriter
     *
     * @param from_url,to_url Copy the contents from the file in path from_url to the file in path to_url
     *                        Read a line, add line num before the line and write the line, and then create a new line
     */
    public static int useBufferedWriter(String from_url, String to_url) {
        String thisLine;
        int count = 0;
        try {
            FileReader fileReader = new FileReader(from_url);
            FileWriter fileWriter = new FileWriter(to_url);
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
            while ((thisLine = bufferedReader.readLine()) != null) {
                count++;
                System.out.println(thisLine);
                System.out.println(count+" "+thisLine);
                bufferedWriter.write(count+" "+thisLine);
                bufferedWriter.newLine();
            }
            bufferedWriter.flush();
            System.out.println("--useBufferedWriter-- had read " + count + " lines. \n--useBufferedWriter-- had writer "+count+" lines.");
        } catch (IOException e) {
            e.printStackTrace();
            return 0;
        }
        return 1;
    }
}