java IO文件操作入门经典例子
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。
在公司没活干，复习了一下IO，发现很多都忘记了，所以写的不好，只够初学用。我把我复习过程中写的代码贴出来，大家共同学习，并请多指教指教哈。顺便一起讨论IO
1、文件拷贝
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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();
}
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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
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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();
}
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3、 从文件（d:\test.txt）中查出字符串”aa”出现的次数
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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();
}
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4、 三种方法读取文件
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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();
}
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5、三种方法写文件
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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();
}
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6、读取文件，并把读取的每一行存入double型数组中
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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();
}
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