【好程序员特训营】Java的Io操作

Java IO的一般使用原则：

一、按数据来源（去向）分类：
1、是文件： FileInputStream, FileOutputStream, FileReader, FileWriter
2、是byte[]：ByteArrayInputStream, ByteArrayOutputStream
3、是Char[]: CharArrayReader, CharArrayWriter
4、是String: StringBufferInputStream, StringReader, StringWriter
5、网络数据流：InputStream, OutputStream, Reader, Writer

二、按是否格式化输出分：
1、要格式化输出：PrintStream, PrintWriter

三、按是否要缓冲分：
1、要缓冲：BufferedInputStream, BufferedOutputStream, BufferedReader, BufferedWriter

四、按数据格式分：
1、二进制格式（只要不能确定是纯文本的）: InputStream, OutputStream及其所有带Stream结束的子类
2、纯文本格式（含纯英文与汉字或其他编码方式）；Reader, Writer及其所有带Reader, Writer的子类

五、按输入输出分：
1、输入：Reader, InputStream类型的子类
2、输出：Writer, OutputStream类型的子类

文件拷贝

try {
            File inputFile = new File(args[0]);
            if (!inputFile.exists()) {
                System.out.println("源文件不存在，程序终止");
                System.exit(1);
            }
            File outputFile = new File(args[1]);
            InputStream in = new FileInputStream(inputFile);
            OutputStream out = new FileOutputStream(outputFile);
 
            byte date[] = new byte[1024];
            int temp = 0;
            while ((temp = in.read(date)) != -1) {
                out.write(date);
            }
 
            in.close();
            out.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

java读文件:实现统计某一目录下每个文件中出现的字母个数、数字个数、空格个数及行数，除此之外没有其他字符

 String fileName = "D:/date.java.bak";
        // String fileName = "D:/test.qqq";
        String line;
        int i = 0, j = 0, f = 0, k = 0;
        try {
            BufferedReader in = new BufferedReader(new FileReader(fileName));
            line = in.readLine();
            while (line != null) {
                // System.out.println(line);
                char c[] = line.toCharArray();
                for (int i1 = 0; i1 < c.length; i1++) {
                    // 如果是字母
                    if (Character.isLetter(c[i1]))
                        i++;
                    // 如果是数字
                    else if (Character.isDigit(c[i1]))
                        j++;
                    // 是空格
                    else if (Character.isWhitespace(c[i1]))
                        f++;
                }
                line = in.readLine();
                k++;
            }
            in.close();
            System.out
                    .println("字母:" + i + ",数字:" + j + ",空格:" + f + ",行数:" + k);
        } catch (IOException e) {
            e.printStackTrace();
        }

从文件（d:\test.txt）中查出字符串”aa”出现的次数

try {
            BufferedReader br = new BufferedReader(new FileReader(
                    "D:\\test.txt"));
            StringBuilder sb = new StringBuilder();
            while (true) {
                String str = br.readLine();
                if (str == null)
                    break;
                sb.append(str);
            }
            Pattern p = Pattern.compile("aa");
            Matcher m = p.matcher(sb);
            int count = 0;
            while (m.find()) {
                count++;
            }
            System.out.println("\"aa\"一共出现了" + count + "次");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }