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:\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();

}

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();

}