文件输入输出I/O

File主要用于在磁盘上读写文件
1、在程序中,用File和JFileChoose让用户定义或者指定一个文件
2、在文件中，用FileOutputStream和FileInputStream读写字节
3、在文件中，用DataOutputStream和DataInputStream读写原始数据类型值
4、在文件中，用PrintWriter和BufferedReader读写对象
5、在文件中，用ObjectOutputStream和ObjectInputStream读写对象
文件输入输出中常见对象的方法如下：
File对象的几个常用方法:
①exists():文件是否存在
②isFile():判断是否是文件还是目录（真为文件，假为目录）
③list()：文件列表，需用String filename[]接受
④length()：检测文件大小

FileOutputStream对象的方法：
①outStream.write(字节数组名或数组);
②outStream.close();

FileInputStream对象的方法：
①inStream.read(字节数组名或数组);
②inStream.close();

DataOutputStream对象的方法
①各种基本数据类型：outDataStream.writeInt()/writeLong()/writeFloat()/writeDouble()/writeChar()/writeBoolean()等
②outDataStream.close()
DataInputStream对象的方法:
①各种基本数据类型：inDataStream.readInt()/readLong()/readFloat()/readDouble()/readChar()/readBoolean()等
②inDataStream.close();

PrintWriter对象的方法：
①print()
②println()

ObjectOutputStream对象的方法
①outObjectStream.writeObject()/其他跟DataOutputStream对象的方法一样
②outObjectStream.close()

ObjectInputStream对象的方法
①inObjectStream.readObject()
②inObjectStream.close()

文件输入输出步骤：
一、低级文件操作：
1、输出
File outFile = new File("sample.txt");
FileOutputStream outStream = new FileOutputStream(outFile);
byte[] byteArray = {10,20,30};
outStream.write(byteArray );
outStream.close();
2、输入
File inFile = new File("sample.txt");
FileInputStream inStream = new FileInputStream(inFile);
int fileSize = (int)inFile.length();
byte[] byteArray = new byte[fileSize ];
inStream.read(byteArray);
inStream.close;


二、高级文件操作
（1）基本数据类型操作
1、输出
File outFile = new File("sample.txt");
FileOutputStream outFileStream = new FileOutputStream(outFile);
DataOutputStream outDataStream = new DataOutputStream(outFileStream);
outDataStream.writeInt()/writeChar()/...;
outDataStream.close();
2、输入
File inFile = new File("sample.txt");
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
inDataStream.readInt()/readChar()/...;
inDataStream.close();


(2)字符串数据类型操作
1、输出
File outFile = new File("sample.txt");
FileOutputStream outFileStream = new FileOutputStream(outFile);
PrintWriter outStream = new PrintWriter(outFileStream);
outStream.println("hello");
outStream.close();

2、输入
File inFile = new File("sample.txt");
FileReader fileReader = new FileReader(inFile);
BufferedReader bufReader = new BufferedReader(fileReader);
String str = bufReader.readLine();
再进行各种类型转换
如：int i = Integer.parseInt(str);
bufReader.close();
三、对象的输入和输出
前提：定义对象的类要实现序列化(implements Serializable)
1、输出
File outFile = new File("sample.txt");
FileOutputStream outFileStream = new FileOutputStream(outFile);
ObjectOutputStream outObjectStream = new ObjectOutputStream(outFileStream);
产生一对象例：Person person = new Person("zhangsan",21,"male");
outObjectStream.writeObject(person);
outObjectStream.close();

2、输入
File inFile = new File("sample.txt");
FileInputStream inFileStream = new FileInputStream(inFile);
ObjectInputStream inObjectStream = new ObjectInputStream(inFileStream);
//用一个对象接受:
Person person;
person = inObjectStream.readObject();
inObjectStream.close();

From http://shang.iteye.com/blog/165947