黑马程序员JAVA编程阶梯基础篇之第二十一章.doc

【济南中心】JAVA编程阶梯：基础篇之第二十一章

IO流字符流FileReader
字符流是什么
字符流是能够直接读写字符IO流
字符流读取字符, 就要先读取到字节数据, 然后转为字符. 假如要写出字符, 需要把字符转为字节再写出.    
FileReader类read()方法能够按照字符大小读取

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FileReader fr = new FileReader("text.txt");    //创建输入流对象,关联aaa.txt
  int ch;
  while((ch = fr.read()) != -1) {       //将读到字符赋值给ch
   System.out.println((char)ch);      //将读到字符强转后打印
  }
  fr.close();            //关流
IO流字符流FileWriter
FileWriter类write()方法能够自动把字符转为字节写出
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FileWriter fw = new FileWriter("text.txt");
                fw.write("text");
                fw.close();
IO流字符流拷贝
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FileReader fr = new FileReader("a.txt");
        FileWriter fw = new FileWriter("b.txt");
        int ch;
        while((ch = fr.read()) != -1) {
                fw.write(ch);
        }
        fr.close();
        fw.close();
IO流使用指定码表读写字符
FileReader是使用默认码表读取文件, 假如需要使用指定码表读取, 那么能够使用InputStreamReader(字节流,编码表)
FileWriter是使用默认码表写出文件, 假如需要使用指定码表写出, 那么能够使用OutputStreamWriter(字节流,编码表)
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BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("UTF-8.txt"), "UTF-8"));                                                                   //高效用指定编码表读
             BufferedWriter bw =   new BufferedWriter(new OutputStreamWriter(new FileOutputStream("GBK.txt"), "GBK"));                                                                   //高效用指定编码表写
             int ch;
             while((ch = br.read()) != -1) {
                     bw.write(ch);
             }
             br.close();
             bw.close();
什么情况下使用字符流
字符流也能够拷贝文本文件, 但不推荐使用. 因为读取时会把字节转为字符, 写出时还要把字符转回字节.
程序需要读取一段文本, 或者需要写出一段文本时候能够使用字符流
读取时候是按照字符大小读取,不会出现半个汉字
写出时候能够直接将字符串写出,不用转换为字节数组
字符流不能够拷贝非纯文本文件，因为在读时候会将字节转换为字符,在转换过程中,可能找不到对应字符,就会用?代替,写出时候会将字符转换成字节写出去，假如是?,直接写出,这么写出之后文件就乱了,看不了了  
IO流自定义字符数组拷贝
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FileReader fr = new FileReader("aaa.txt");                        //创建字符输入流,关联aaa.txt
          FileWriter fw = new FileWriter("bbb.txt");               //创建字符输出流,关联bbb.txt

          int len;
          char[] arr = new char[1024*8];                                        //创建字符数组
          while((len = fr.read(arr)) != -1) {                                //将数据读到字符数组中
                  fw.write(arr, 0, len);                                        //从字符数组将数据写到文件上
          }   
          fr.close();                                                        //关流释放资源
          fw.close();
IO流带缓冲字符流
BufferedReaderread()方法读取字符时会一次读取若干字符到缓冲区, 然后逐一返回给程序, 降低读取文件次数, 提升效率
BufferedWriterwrite()方法写出字符时会先写到缓冲区, 缓冲区写满时才会写到文件, 降低写文件次数, 提升效率
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BufferedReader br = new BufferedReader(new FileReader("aaa.txt"));        //创建字符输入流对象,关联aaa.txt
                BufferedWriter bw = new BufferedWriter(new FileWriter("bbb.txt"));     //创建字符输出流对象,关联bbb.txt

                int ch;                               
                while((ch = br.read()) != -1) {         //read一次,会先将缓冲区读满,从缓冲去中一个一个返给暂时变量ch
                        bw.write(ch);                            //write一次,是将数据装到字符数组,装满后再一起写出去
                }
                br.close();                                                        //关流
                bw.close();
IO流readLine()和newLine()方法
BufferedReaderreadLine()方法能够读取一行字符(不包含换行符号)
BufferedWriternewLine()能够输出一个跨平台换行符号"\r\n"
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BufferedReader br = new BufferedReader(new FileReader("aaa.txt"));
                BufferedWriter bw = new BufferedWriter(new FileWriter("bbb.txt"));
                String line;
                while((line = br.readLine()) != null) {
                        bw.write(line);
                        //bw.write("\r\n");                                        //只支持windows系统
                        bw.newLine();                                                //跨平台
                }
                br.close();
                bw.close();
IO流LineNumberReader
LineNumberReader是BufferedReader子类, 具备相同功效, 而且能够统计行号
调用getLineNumber()方法能够获取当前行号
调用setLineNumber()方法能够设置当前行号
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LineNumberReader lnr = new LineNumberReader(new FileReader("aaa.txt"));
                String line;
                lnr.setLineNumber(100);                                                                        //设置行号
                while((line = lnr.readLine()) != null) {
                        System.out.println(lnr.getLineNumber() + ":" + line);//获取行号
                }

                lnr.close();
装饰设计模式
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interface Coder {
                        public void code();
                }

                class Student implements Coder {

                        @Override
                        public void code() {
                                System.out.println("javase");
                                System.out.println("javaweb");
                        }

                }

                class HeiMaStudent implements Coder {
                        private Student s;                                                //获取到被包装类引用
                        public ItcastStudent(Student s) {                //经过结构函数创建对象时候,传入被包装对象
                                this.s = s;
                        }
                        @Override
                        public void code() {                                        //对其原有功效进行升级
                                s.code();
                                System.out.println("数据库");
                                System.out.println("ssh");
                                System.out.println("安卓");
                                System.out.println(".....");
                        }

                }
IO流递归遍历删除文件夹
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class RemoveDir{ 
    public static void main(String[] args){ 
        File dir = new File("E:\\kankan"); 
        removeDir(dir); 
    } 

    public static void removeDir(File dir){ //删除dir目录下全部内容 
        File[] files = dir.listFiles(); //列出全部文件及目录，返回File[] 

        for(int x=0; x<files.length; x++){ 
            if(files[x].isDirectory()) //若是目录，继续递归调用 
                removeDir(files[x]); 
            else 
                System.out.println(files[x].toString()+"::file::"+files[x].delete()); 
        } 

        //继续删除空目录 
        System.out.println(dir+"::dir::"+dir.delete()); 
    } 
}