第三题 请用键盘循环随机输入三段字符串1：将三段字符串用Stringbuffer类拼接成一个字符串并将该字符串写入cinputDemotxt文件；写文件用字节流实现2：读取cinputDemotxt文件并打印文件内容读文件用字节流实现3：将cinputDemotxt文件中的内容复制到cinputDemo2txt文件中读写文件用字节流实现

import java.io.*;

public class InputDemo {

public static void main(String[] args) throws IOException {
    String str1, str2, str3;

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.println("请输入第一个字符串：");
    str1 = br.readLine();

    System.out.println("请输入第二个字符串：");
    str2 = br.readLine();

    System.out.println("请输入第三个字符串：");
    str3 = br.readLine();

    // 拼接字符串
    StringBuffer sb = new StringBuffer();
    sb.append(str1).append(str2).append(str3);
    String content = sb.toString();

    // 写入文件
    FileOutputStream fos = new FileOutputStream("c:\\inputDemo.txt");
    fos.write(content.getBytes());

    // 读取文件
    FileInputStream fis = new FileInputStream("c:\\inputDemo.txt");
    int len = 0;
    byte[] buffer = new byte[1024];
    while ((len = fis.read(buffer)) != -1) {
        System.out.print(new String(buffer, 0, len));
    }

    // 复制文件
    FileInputStream fis2 = new FileInputStream("c:\\inputDemo.txt");
    FileOutputStream fos2 = new FileOutputStream("c:\\inputDemo2.txt");
    len = 0;
    while ((len = fis2.read(buffer)) != -1) {
        fos2.write(buffer, 0, len);
    }

    fos.close();
    fis.close();
    fis2.close();
    fos2.close();
}

} ``