IO流

 1.用FileInputStream读文件内容，然后再用OutputStream来向文件中写入内容

public class IO1 {
    public static void main(String[] args) throws Exception{

        File file=new File("G://ha_xie/a.txt");
        InputStream in=new FileInputStream(file);
        //读     里面的参数是  从此输入流读取的估计字节数
        byte[] b=new byte[in.available()];
        in.read(b);
        //将字节数组转换成字符串
        String str=new String(b,0,b.length);
        System.out.println(str);

        OutputStream out=new FileOutputStream("G://ha_xie/b.txt");
        out.write(b);//将数组中的字节写入此输出流
    }
}

2.使用InputStreamReader和OutputStreamWriter

public class IO2 {
    public static void main(String[] args)throws Exception {
        File file=new File("G://ha_xie/a.txt");
        InputStream in=null;
        in=new FileInputStream(file);
        InputStreamReader is = new InputStreamReader(in);
        char[] c=new char[30];
        is.read(c);
        //字符数组在转换成字符串
        String str=new String(c);
        System.out.println(str);
//        in.close();
//        is.close();
        //写到c.txt
        OutputStream out=new FileOutputStream("G://ha_xie/d.txt");
        OutputStreamWriter os1=new OutputStreamWriter(out);
        os1.write(str);
        os1.close();//这个必须关闭，才能向文件里面写入内容
    }
}

3.使用FileReader和FileWriter

public class IO3 {
    public static void main(String[] args)throws Exception {
        Reader r= new FileReader("G://ha_xie/a.txt");
        char[] c=new char[20];
        r.read(c);
        System.out.println(new String(c));

        Writer w=new FileWriter("G://ha_xie/bb.txt");
        w.write(c);
        w.close();
    }
}

 4.使用BufferedReader和BufferedWriter

public class IO4 {
    public static void main(String[] args) throws Exception{
        //字节流
        InputStream in=new FileInputStream("G://ha_xie./a.txt");
        //字符流
        InputStreamReader r=new InputStreamReader(in);
        //缓冲流
        Reader reader1=new BufferedReader(new FileReader("G://ha_xie/b.txt"));
        Reader reader=new BufferedReader(r);
        /*String str=((BufferedReader) reader).readLine();//按行读
        System.out.println(str);*/
        /*String s;
        int i=0;
        while((s=((BufferedReader) reader).readLine())!=null){
            System.out.println(s);
            i++;
        }
        System.out.println(i);*/
        String string = ((BufferedReader) reader).readLine();
        String string2 = ((BufferedReader) reader).readLine();
        System.out.println(string);
        System.out.println(string2);
        //关闭资源
        reader.close();
        r.close();
        in.close();
        //写
        BufferedWriter bw=new BufferedWriter(new FileWriter("G://ha_xie/oo.txt"));
        bw.write("谢军帅谢军帅");
        bw.newLine();//换行，写入一个行分隔符
        bw.newLine();
        bw.write("xiejunshuaixiejunshuai");
        bw.flush();//刷新
        bw.close();//关闭此流，但要先刷新它
    }
}
//我的理解：是缓冲中的数据，输出一行少一行

注意：使用完流对象之后，要关闭！！！要不然会存在写不进去的情况。