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Java Platform 1.2 |
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java.lang.Object
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+--java.io.InputStream
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+--java.io.FilterInputStream
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+--java.io.PushbackInputStream
A PushbackInputStream adds
functionality to another input stream, namely
the ability to "push back" or "unread"
one byte. This is useful in situations where
it is convenient for a fragment of code
to read an indefinite number of data bytes
that are delimited by a particular byte
value; after reading the terminating byte,
the code fragment can "unread" it, so that
the next read operation on the input stream
will reread the byte that was pushed back.
For example, bytes representing the characters
constituting an identifier might be terminated
by a byte representing an operator character;
a method whose job is to read just an identifier
can read until it sees the operator and
then push the operator back to be re-read.
| Field Summary | |
protected byte[] |
buf
The pushback buffer. |
protected int |
pos
The position within the pushback buffer from which the next byte will be read. |
| Fields inherited from class java.io.FilterInputStream |
in |
| Constructor Summary | |
PushbackInputStream(InputStream in)
Creates a PushbackInputStream
and saves its argument, the input stream
in, for later use. |
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PushbackInputStream(InputStream in,
int size)
Creates a PushbackInputStream
with a pushback buffer of the specified size,
and saves its argument, the input stream
in, for later use. |
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| Method Summary | |
int |
available()
Returns the number of bytes that can be read from this input stream without blocking. |
void |
close()
Closes this input stream and releases any system resources associated with the stream. |
boolean |
markSupported()
Tests if this input stream supports the mark and
reset methods, which it does not. |
int |
read()
Reads the next byte of data from this input stream. |
int |
read(byte[] b,
int off,
int len)
Reads up to len bytes of data from this input stream into
an array of bytes. |
long |
skip(long n)
Skips over and discards n bytes of data from this
input stream. |
void |
unread(byte[] b)
Pushes back an array of bytes by copying it to the front of the pushback buffer. |
void |
unread(byte[] b,
int off,
int len)
Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. |
void |
unread(int b)
Pushes back a byte by copying it to the front of the pushback buffer. |
| Methods inherited from class java.io.FilterInputStream |
mark,
read,
reset |
| Methods inherited from class java.lang.Object |
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait |
| Field Detail |
protected byte[] buf
protected int pos
pos is equal to
buf.length; when the buffer is full, pos is
equal to zero.| Constructor Detail |
public PushbackInputStream(InputStream in,
int size)
PushbackInputStream
with a pushback buffer of the specified size,
and saves its argument, the input stream
in, for later use. Initially,
there is no pushed-back byte (the field
pushBack is initialized to
-1).in - the input stream from which bytes will be read.size - the size of the pushback buffer.public PushbackInputStream(InputStream in)
PushbackInputStream
and saves its argument, the input stream
in, for later use. Initially,
there is no pushed-back byte (the field
pushBack is initialized to
-1).in - the input stream from which bytes will be read.| Method Detail |
public int read()
throws IOException
int in the range
0 to 255. If no byte is available
because the end of the stream has been reached, the value
-1 is returned. This method blocks until input data
is available, the end of the stream is detected, or an exception
is thrown.
This method returns the most recently pushed-back byte, if there is
one, and otherwise calls the read method of its underlying
input stream and returns whatever value that method returns.
-1 if the end of the
stream has been reached.InputStream.read()
public int read(byte[] b,
int off,
int len)
throws IOException
len bytes of data from this input stream into
an array of bytes. This method first reads any pushed-back bytes; after
that, if fewer than than len bytes have been read then it
reads from the underlying input stream. This method blocks until at
least 1 byte of input is available.b - the buffer into which the data is read.off - the start offset of the data.len - the maximum number of bytes read.-1 if there is no more data because the end of
the stream has been reached.InputStream.read(byte[], int, int)
public void unread(int b)
throws IOException
(byte)b.b - the int value whose low-order
byte is to be pushed back.
public void unread(byte[] b,
int off,
int len)
throws IOException
b[off], the byte after that will
have the value b[off+1], and so forth.b - the byte array to push back.off - the start offset of the data.len - the number of bytes to push back.
public void unread(byte[] b)
throws IOException
b[0], the byte after that will have the
value b[1], and so forth.b - the byte array to push back
public int available()
throws IOException
available method
of the underlying input stream; it returns that value plus the number of
bytes that have been pushed back.FilterInputStream.in,
InputStream.available()
public long skip(long n)
throws IOException
n bytes of data from this
input stream. The skip method may, for a variety of
reasons, end up skipping over some smaller number of bytes,
possibly zero. If n is negative, no bytes are skipped.
The skip method of PushbackInputStream
first skips over the bytes in the pushback buffer, if any. It then
calls the skip method of the underlying input stream if
more bytes need to be skipped. The actual number of bytes skipped
is returned.
n - the number of bytes to be skipped.FilterInputStream.in,
InputStream.skip(long n)public boolean markSupported()
mark and
reset methods, which it does not.false, since this class does not support the
mark and reset methods.InputStream.mark(int),
InputStream.reset()
public void close()
throws IOException
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Java Platform 1.2 |
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