java IO文件操作简单基础入门例子，IO流其实没那么难

IO是JAVASE中非常重要的一块，是面向对象的完美体现，深入学习IO，你将可以领略到很多面向对象的思想。
今天整理了一份适合初学者学习的简单例子，让大家可以更深刻的理解IO流的具体操作。

1、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();

        }

 

 

2、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();

        }

 

 

 

3、 从文件（d: est.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();

        }

 

 

 

 

4、 三种方法读取文件

try {

           // 方法一

           BufferedReader br = new BufferedReader(new FileReader(new File(

                   "D:\1.xls")));

           // StringBuilder bd = new StringBuilder();

           StringBuffer bd = new StringBuffer();

           while (true) {

               String str = br.readLine();

               if (str == null) {

                   break;

               }

               System.out.println(str);

               bd.append(str);

           }

           br.close();

           // System.out.println(bd.toString());

           // 方法二

           InputStream is = new FileInputStream(new File("d:\1.xls"));

           byte b[] = new byte[Integer.parseInt(new File("d:\1.xls").length()

                   + "")];

           is.read(b);

           System.out.write(b);

           System.out.println();

           is.close();

           // 方法三

           Reader r = new FileReader(new File("d:\1.xls"));

           char c[] = new char[(int) new File("d:\1.xls").length()];

           r.read(c);

           String str = new String(c);

           System.out.print(str);

           r.close();

       } catch (RuntimeException e) {

           // TODO Auto-generated catch block

           e.printStackTrace();

       } catch (FileNotFoundException e) {

           // TODO Auto-generated catch block

           e.printStackTrace();

       } catch (IOException e) {

           // TODO Auto-generated catch block

           e.printStackTrace();

       }

 

5、三种方法写文件   

 

try {

           PrintWriter pw = new PrintWriter(new FileWriter("d:\1.txt"));

           BufferedWriter bw = new BufferedWriter(new FileWriter(new File(

                   "d:\1.txt")));

           OutputStream os = new FileOutputStream(new File("d:\1.txt"));

           // 1

           os.write("ffff".getBytes());

           // 2

           // bw.write("ddddddddddddddddddddddddd");

           // 3

           // pw.print("你好sssssssssssss");

           bw.close();

           pw.close();

           os.close();

       } catch (IOException e) {

           // TODO Auto-generated catch block

           e.printStackTrace();

       }

 

 

[代码]6、读取文件，并把读取的每一行存入double型数组中

try {

            BufferedReader br = new BufferedReader(new FileReader(new File(

                    "d:\2.txt")));

            StringBuffer sb = new StringBuffer();

            while (true) {

                String str = br.readLine();

                if (str == null) {

                    break;

                }

                sb.append(str + "、");

            }

            String str = sb.toString();

            String s[] = str.split("、");

            double d[] = new double[s.length];

            for (int i = 0; i < s.length; i++) {

                d[i] = Double.parseDouble(s[i]);

            }

            for (int i = 0; i < d.length; i++) {

                System.out.println(d[i]);

            }

            br.close();

        } catch (FileNotFoundException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (IOException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }