Java IO.pdf - Nguyen Dang Binh

Java I/O
The writeChar() method writes a single, two-byte Unicode character. This method does not
use UTF-8 encoding. It simply writes the two bytes of the character in big-endian order.
writeChars() writes each character in the String argument to the underlying output stream
as a two-byte, Unicode character; it also does not use UTF-8 encoding. And the
writeBytes() method writes the low-order byte of each character in the String argument to
the underlying output stream. Any information in the high-order byte is lost. In other words, it
assumes the string is given in ISO-Latin-1 and contains only characters whose value is
between and 255.
The writeUTF() method, however, retains the information in the high-order byte as well as
the length of the string. First it writes the number of characters in the string onto the
underlying output stream as a two-byte unsigned int between and 65,535. Next it encodes the
string in UTF-8 and writes the bytes of the encoded string to the underlying output stream.
This allows a data input stream reading those bytes to completely reconstruct the string.
However, strings longer than 65,535 characters are a problem. If you pass a string longer than
65,535 characters to writeUTF(), writeUTF() throws a java.io.UTFDataFormat-
Exception , a subclass of IOException , and doesn't write any of the data. Although 65,535
characters seems like a large limit, I can imagine reaching it if you're writing a word
processor, text editor, or web browser and trying to save your data by writing it out as a single
string. If you are writing a program that needs to deal with large blocks of text, you should
write your own file format and save routine rather than relying on writeUTF().
7.6.3 Reading Text
The DataInputStream class has three methods to read text data. These are:
public final char readChar() throws IOException
public final String readUTF() throws IOException
public static final String readUTF(DataInput in) throws IOException
The readChar() method reads two bytes from the underlying input stream, interprets them as
a big-endian Unicode character, and returns that character as a Java char. An IOException is
thrown if the underlying input stream's read() method throws an IOException. An
EOFException may be thrown if you're within one byte of the end of the stream and therefore
a complete char can't be read.
The noargs readUTF() method reads and returns a string that was written in Java's pseudo-
UTF-8 encoding with a two-byte, unsigned length prefix (in other words, a string written by
writeUTF() in DataOutputStream). An EOFException is thrown if the end of the stream is
encountered or the stream runs out of data before providing the promised number of
characters. A UTFDataFormatException is thrown if the bytes read do not match the UTF
encoding specification; for example, if four bytes in a row begin with the bit sequence 10. An
IOException is also thrown if the underlying stream throws an IOException.
7.6.4 The Deprecated readLine( ) Method
The DataInputStream class also has a widely used but deprecated readLine() method:
public final String readLine() throws IOException
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