一、javaSE （二十）递归、IO流、自学字符流

1:递归(理解)

         (1)方法定义中调用方法本身的现象

                   举例;老和尚給小和尚讲故事,我们学编程

         (2)递归的注意事项;

                   A:要有出口,否则就是死递归

                   B:次数不能过多,否则内存溢出

                   C:构造方法不能递归使用

         (3)递归的案例

                   A:递归求阶乘

                   B:兔子问题

                   C:递归输出指定目录下所有指定后缀名的文件绝对路径

                   D:递归删除带内容的目录(小心使用)

2:IO流(掌握)

         (1);O用于在设备间进行数据传输的操作

         (2)分类

                   A:流向

                            输入流     读取数据

                            输出流     写出数据

                   B:数据类型

                            字节流

                                     字节输入流

                                     字节输出流

                            字符流

                                     字符输入流

                                     字符输出流

                   注意：

                            a:如果我们没有明确说明按照什么分,默认按照数据类型分

                            b:除非文件用 windows自带的记事本打开我们能够读懂,才采用字符流,否则建议使用字节流

         (3)Fi1eOutputOtream写出数据

                   A:操作步骤

                            a:创建字节输出流对象

                            b:週用 write()方法

                   B:代码体现

                            FileOutputStream fos = new FileOutputStream("fos.txt ");

                            fos.write("he11O".getbytes());

                            fos.close();;

                   C:要注意的问题

                            a:创建字节输出流对象做了几件事情?

                            b:为什么要c1ose()?

                            c:如何实现数据的换行?

                            d:如何实现数据的追加写入?

         (4)Fi1eInputStream读取数据

                   A:操作步骤

                            a:创建字节输入流对象

                            b:调用read()方法

                            c:释放资源

                   B:代码体现

                            Fi1eInputStream fis= new Fi1eInputStream("fos. txt ");

                            //方式1

                            int by = 0;

                            while((by=fis.read())!=-1){

                                     System.out.print((char)by);

                            }

                            //方式2

                            Byte[] bys = new byte[1024];

                            int len =0;

                            while( (len=fis.read (bys))!=-1){

                                     Systen.out.print(new String(bys,0,len));

                            }

         (5)案例:2种实现

                   A:复制文本文件

                   B:复制图片

                   c:复制视频

         (6)字节缓冲区流

                   A: BufferedOutputStream

                   B: BufferedInputStream

         (7)案例:4种实现

                   A:复制文本文件

                   B:复制图片

                   C:复制视频

3:自学字符流

         IO流分类

                   字节流

                   InputStream

                            FileInputStream

                            BufferedInputStream

                   OutputStream

                            FileOutputStream

                            BufferedOutputStream

         字符流

                   Reader

                            FileReader

                            BufferedReader

                   Writer

                            FileWriter

                            BufferedWriter