Sun Tutorial:JAVA中的 I/O 流

这是Sun网站上关于JAVA I/O流的学习指南.



1.Byte streams should only be used for the most primitive I/O.
So why talk about byte streams? Because all other stream types are built on byte streams.All byte stream classes are descended from InputStream and OutputStream.
File I/O byte streams: FileInputStream and FileOutputStream.

2.The Java platform stores character values using Unicode conventions. Character stream I/O automatically translates this internal format to and from the local character set. In Western locales, the local character set is usually an 8-bit superset of ASCII.
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3.If internationalization isn't a priority, you can simply use the character stream classes without paying much attention to character set issues. Later, if internationalization becomes a priority, your program can be adapted without extensive recoding.

4.All character stream classes are descended from Reader and Writer. As with byte streams, there are character stream classes that specialize in file I/O: FileReader and.

5.Most of the examples we've seen so far use unbuffered I/O. This means each read or write request is handled directly by the underlying OS. This can make a program much less efficient, since each such request often triggers disk access, network activity, or some other operation that is relatively expensive.

6.Buffered input streams read data from a memory area known as a buffer; the native input API is called only when the buffer is empty. Similarly, buffered output streams write data to a buffer, and the native output API is called only when the buffer is full.

7.There are four buffered stream classes used to wrap unbuffered streams: BufferedInputStream and BufferedOutputStream create buffered byte streams, while BufferedReader and BufferedWriter create buffered character streams.

8.It often makes sense to write out a buffer at critical points, without waiting for it to fill. This is known as flushing the buffer. To flush a stream manually, invoke its flush method. The flush method is valid on any output stream, but has no effect unless the stream is buffered.

9.The scanner API breaks input into individual tokens associated with bits of data.By default, a scanner uses white space to separate tokens. The formatting API assembles data into nicely formatted, human-readable form.

10.Scanner also supports tokens for all of the Java language's primitive types (except for char), as well as BigInteger and BigDecimal. Also, numeric values can use thousands separators. Thus, in a US locale, Scanner correctly reads the string "32,767" as representing an integer value.

11.Stream objects that implement formatting are instances of either PrintWriter, a character stream class, and PrintStream, a byte stream class.

12.A program is often run from the command line and interacts with the user in the command line environment. The Java platform supports this kind of interaction in two ways: through the Standard Streams and through the Console.

13.The Java platform supports three Standard Streams: Standard Input, accessed through System.in; Standard Output, accessed through System.out; and Standard Error, accessed through System.err.

14.You might expect the Standard Streams to be character streams, but, for historical reasons, they are byte streams. System.out and System.err are defined as PrintStream objects. Although it is technically a byte stream, PrintStream utilizes an internal character stream object to emulate many of the features of character streams. By contrast, System.in is a byte stream with no character stream features. To use Standard Input as a character stream, wrap System.in in InputStreamReader.

15.A more advanced alternative to the Standard Streams is the Console. This is a single, predefined object of type Console that has most of the features provided by the Standard Streams, and others besides. The Console is particularly useful for secure password entry. The Console object also provides input and output streams that are true character streams, through its reader and writer methods.