Java IO.pdf - Nguyen Dang Binh

Java I/O
The java.util.jar package includes two stream classes for reading files from JAR archives.
These will also be discussed in Chapter 9.
JarInputStream JarOutputStream
The java.security package includes a couple of stream classes used for calculating
message digests:
DigestInputStream DigestOutputStream
The Java Cryptography Extension (JCE) adds two classes for encryption and decryption:
CipherInputStream CipherOutputStream
These four streams will be discussed in Chapter 10.
Finally, there are a few random stream classes hiding inside the sun packages—for example,
sun.net.TelnetInputStream and sun.net.TelnetOutputStream . However, these are
deliberately hidden from you and are generally presented as instances of
java.io.InputStream or java.io.OutputStream only.
1.2 Numeric Data
Input streams read bytes and output streams write bytes. Readers read characters and writers
write characters. Therefore, to understand input and output, you first need a solid
understanding of how Java deals with bytes, integers, characters, and other primitive data
types, and when and why one is converted into another. In many cases Java's behavior is not
obvious.
1.2.1 Integer Data
The fundamental integer data type in Java is the int, a four-byte, big-endian, two's
complement integer. An int can take on all values between -2,147,483,648 and
2,147,483,647. When you type a literal integer like 7, -8345, or 3000000000 in Java source
code, the compiler treats that literal as an int. In the case of 3000000000 or similar numbers
too large to fit in an int, the compiler emits an error message citing "Numeric overflow."
longs are eight-byte, big-endian, two's complement integers with ranges from -
9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. long literals are indicated by
suffixing the number with a lower- or uppercase L. An uppercase L is preferred because the
lowercase l is too easily confused with the numeral 1 in most fonts. For example, 7L, -8345L,
and 3000000000L are all 64-bit long literals.
There are two more integer data types available in Java, the short and the byte. shorts are
two-byte, big-endian, two's complement integers with ranges from -32,768 to 32,767. They're
rarely used in Java and are included mainly for compatibility with C.
bytes, however, are very much used in Java. In particular they're used in I/O. A byte is an
eight-bit, two's complement integer that ranges from -128 to 127. Note that like all numeric
17