Java IO文件输入输出详解

java.io.File and Scanner

File represent either the name of a particular file or the names of a set of files in a directory. Use Scanner class for reading text files.

Read From A Disk File：

1 File inputFile = new File("input.txt"); 2 Scanner in = new Scanner(inputFile); 3 while (in.hasNextDouble()){ 4 double value = in.nextDouble(); 5 }

Using Input Streams

Methods common to all input streams:

1 int read() throws IOException 2 //reads one byte (character) of data 3 void reset() throws IOException 4 //starts stream over so its bytes can be read again 5 void close() throws IOException 6 //notifies stream you are finished using it

Using Output Streams

Methods common to all output streams:

1 void write(int n) throws IOException 2 //writes one byte (character) of data 3 void flush() throws IOException 4 //writes any bytes that were waiting to be written 5 void close() throws IOException 6 //notifies stream you are finished using it

InputStreamReader

1、This is a bridge between bytes and chars. 2、The read() method returns an int, which must be cast to a char. 3、read() returns -1 if the end of the stream has been reached. Thus the program above will never stop, since we can’t type the “end-of-stream” value.

System.in: byte stream

1 public static void main(String[] args) { 2 InputStreamReader isr = new InputStreamReader(System.in); 3 int c; 4 try { 5 while ((c = isr.read()) != -1) 6 System.out.println((char) c); 7 } catch(IOException e) { 8 //… 9 } 10 } 1 public static void main(String[] args) throws IOException { 2 InputStreamReader isr = new InputStreamReader(new FileInputStream("FileInput.java")); 3 int c; 4 while ((c = isr.read()) != -1) 5 System.out.println((char) c); 6 isr.close(); 7 }

BufferedReader

1 public static void main(String[] args) { 2 BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 3 String s; 4 try { 5 while ((s = br.readLine()).length() != 0) 6 System.out.println(s); 7 } catch(IOException e) { 8 //… 9 } 10 }

also:

1 BufferedReader br2 = new BufferedReader(new FileReader(“hardcode.txt”)); 2 String anotherLine = br2.readLine(); 3 br2.close();

PrintWriter

1、To write to a file, construct a PrintWriter object: PrintWriter out = new PrintWriter("out.txt"); 2、If file already exists, it is emptied before the new data are written into it. 3、If file doesn’t exist, an empty file is created. 4、Use print and println to write into a PrintWriter: out.println("Hello, World!"); out.printf("Total: %8.2f\n", total); 5、You must close a file when you are done processing it: in.close(); out.close();Otherwise, not all of the output may be written to the disk file. 6、Always specify “UTF-8” as the second parameter when construction a Scanner or a PrintWriter.

Transient variables

Instance variables that you do not wish to save (or can’t save, because they are not serializable) can be declared with transient modifier (or static) private transient TextReader in;

I/O Exception

IOException ChangedCharSetException CharConversionException EOFException FileNotFoundException InterruptedIOException MalformedURLException ObjectStreamException ProtocolException RemoteException SocketException SyncFailedException UnknownHostException UnknownServiceException UnsupportedEncodingException UTFDataFormatException ZipException